Brea City Council
June 2, 2026

We submit these comments to express Hills for Everyone’s concerns regarding the proposed Project’s potentially significant impacts on the area’s natural resources and the environment.

I. Introduction and Background
As proposed, the Brea GPU and BCSP (“Project”) would allow significant amounts of new development in Brea, summarized in NOP Table 1:

Residential
Units
Population Non-Residential Square
Footage (NRSF)
Jobs
Existing Conditions (2025) 16,345 46,585 21,480,414 51,937 Proposed GPU and BCSP
(2050 horizon)
23,736 67,647 30,587,193 73,709
Increase
(Subject of EIR analysis)
7,391 units
(31% increase)
21,062 persons
(31% increase)
9,106,779 square feet
(30% increase)
21,772 jobs
(30% increase)
This table demonstrates notable changes in the amount of:
• Potential for additional Residential Units and Population in the Hillside Residential, MU-50, Brea 265 Specific Plan, and Proposed Brea Core Study Area GP land use designations; and
• Potential for additional Non-Residential Square Footage and Jobs in the General Commercial, General Industrial, Light Industrial, MU-18, MU-50, Public Facilities, Recreational Commercial, Brea 265 Specific Plan, Brea Industrial Specific Plan, and Proposed Brea Core Study Area GP land use designations.

Increases of roughly 30% in each of the categories above table show the substantial change in the number of people, buildings, and jobs for the City. This growth should be focused in the already-developed areas of the City, which the GPU and BCSP appear to be proposing. However, when examining the environmental impacts of this growth at the programmatic level, the City must disclose all it reasonably can now.

The NOP states that the EIR “will not be as detailed as an EIR on the specific development or construction projects that may follow,” and that the “EIR can serve to streamline environmental review of future projects.” See NOP p. 4. Notably, however, under recently-adopted State legislation including Assembly Bill 130 (2024), many City of Brea
September 24, 2025

projects that conform with the General Plan land use designations and associated zoning will be exempt from further CEQA review. Thus, the General Plan EIR’s analysis may be the first, and last, consideration of environmental impacts from those exempt categories of projects. For this reason, it is imperative that the EIR thoroughly and properly analyze and, if necessary, mitigate for, the potential environmental impacts of the development allowed under the GPU and BCSP. See Cleveland National Forest Foundation v. San Diego Assn. of Governments (2017) 17 Cal.App.5th 413, 441 (program EIRs must provide sufficient detail to decisionmakers so that they can evaluate a project’s environmental impacts). The GPU and BCSP should also consider policies and programs that can serve to reduce the environmental impacts of future development through actions that be taken proactively or in coordination with future projects.

II. Issues to Be Addressed in the EIR
One of CEQA’s fundamental requirements is that an EIR contain an accurate and complete project description. See County of Inyo v. City of Los Angeles (1977) 71 Cal.

App. 3d 18; see also 14 Cal. Code Regs. § 15124 (“CEQA Guidelines”). A clear and comprehensive project description is essential for meaningful public review. The EIR must ensure that the CEQA analysis and Project are aligned and that the Project Description is stable and comprehensive to allow a full understanding of the Project’s anticipated impacts for both the GPU and BCSP.

The Existing GP Land Use Map depicts the land use category for all properties in both the City limits and in the City’s Sphere of Influence (SOI). The Proposed GPU Land Use Map changes the land use designations of all properties that are within a specific plan boundary to the name of the applicable specific plan. For instance, parcels in the Tonner Hills Specific Plan area have Existing GP Land Use Map designations of “Natural Open Space” and “Low Density Residential.” On the Proposed GPU Land Use Map, those parcels now have a GPLU designation of “Tonner Hills Specific Plan.” From that land use designation alone, it is unclear what uses are permitted under the Proposed GPU. The Project Description and accompanying land use maps and tables should clearly indicate the changes between current and proposed land use designations and quantify what those changes mean in terms of development potential. The EIR should also provide a clear list (including Assessor Parcel Numbers and addresses) of all parcels whose General Plan land use designations are proposed to change as a result of the Project.

Second, an EIR must provide enough analysis and detail about environmental impacts to enable decisionmakers to understand the environmental consequences of their decisions. CEQA Guidelines §15151; Kings County Farm Bureau v. City of Hanford (1990) 221 Cal.App.3d 692. To this end, the City must make a good faith effort at full City of Brea
September 24, 2025

disclosure of environmental impacts and must analyze the cumulative impacts of the Project in combination with the effects of other past, current, and reasonably foreseeable future projects in the area. See CEQA Guidelines §§ 15130(a), 15065(c).

Third, CEQA requires that an EIR analyze a range of reasonable alternatives to a project that can feasibly attain most of the basic project objectives while avoiding or substantially lessening the project’s environmental impacts. See Public Resources Code § 21100(b)(4); see also CEQA Guidelines § 15126.6(a). Although the NOP notes that the EIR will evaluate a reasonable range of alternatives, it does not give any indication as to what alternatives may be considered. See NOP p. 5. The City must complete a robust examination of alternatives so the public and decision-makers are able to see the tradeoffs involved in choosing to move forward with either the Project or one of the alternatives.

III. General Plan Policy Considerations
The City of Brea has long supported smart development within the City while celebrating the recreation, open space, and wildlife habitat conservation areas that lie both within and beyond the City limits. The Community Vision Plan published in 2024 was developed to guide the General Plan 2050 effort. The Vision Plan includes a Community Vision Statement, which emphasizes, in part, that “[b]alanced growth and inclusivity are valued. The natural environment, including open spaces, hillsides and wildlife, is well-preserved. The City also provides essential infrastructure and amenities to meet the needs of current and future community members. Diverse representation in decision-making fosters community cohesion. The City preserves what makes it special, while adapting to a changing world and cultivating a prosperous future for all people who live, work, and visit Brea.” See Community Vision Plan p. 1.

Two key Guiding Principles from the Vision Plan are Guiding Principle 5:

Resilience for Future Generations and Guiding Principle 6: Connection to Nature.

Guiding Principle 5 explains how Brea sees itself as a forward-thinking leader ready to take on the challenges of a changing climate. This principle states that “[p]roactive measures to combat extreme weather, including shade tree planting, water management practices, and wildfire preparedness, enhance both environmental sustainability and quality of life. Through these comprehensive efforts, Brea is a resilient, livable community for current and future generations.” See Community Vision Plan p. 6.

Guiding Principle 6 supports Brea’s commitment to providing recreation and open spaces for human and non-humans alike. This principle recognizes that “[T]he surrounding hills and open spaces further enrich Brea’s outdoor offerings, providing opportunities for sports, leisure, and a deeper connection to nature.” See Community Vision Plan p. 7.

City of Brea
September 24, 2025

This General Plan Update is Brea’s opportunity to adopt policies that align with these Guiding Principles and the City’s long-standing conservation values of protecting the hills. The City has repeatedly demonstrated these values through the its support of the Wildlife Corridor Conservation Authority (WCCA), establishment of Chino Hills State Park, and formation of the Hillside Open Space Education Coalition (HOSEC). Brea’s efforts, in combination with those of other local and regional agencies, have resulted in the preservation of significant areas of land in the Puente-Chino Hills corridor. A map prepared by Hills For Everyone illustrates the natural lands in the corridor (Exhibit A) and the accompanying table (Exhibit B) quantifies the financial investment made by public agencies to secure this land for recreation, open space, and habitat preservation.

With this General Plan Update, Brea can implement policies and programs that will further the community vision as well as bolster the substantial public investments already made in open space and habitat preservation.

Brea’s policies can ensure that development in urban areas minimally impacts the adjacent lands and the policies can also serve to mitigate impacts from development under the General Plan. See Pub. Resources Code § 21081.6(b). Hills For Everyone encourages Brea to adopt GPU policies in four key categories: 1) Discouraging development in hillside areas within the Brea’s Sphere of Influence; 2) Emphasizing both fire safety and wildlife protection at the urban edge that is based on sound science and does not remove more protective habitat cover than is necessary; 3) Bringing the General Plan into compliance with new State laws that prioritize wildlife corridors and habitat connectivity; and 4) Supporting urban greening and climate resiliency. The City should consider the follow, non-exhaustive list of potential policies in each of these categories.

Limit Hillside Development Within the Brea Sphere of Influence (SOI). General Plan programs and policies should include:
• Define thresholds for permitting development on parcels in the SOI designated Hillside Residential. Thresholds should include enforcing strict development limits in areas within a Very High Fire Hazard Severity Zone, allowing development only when accompanied by a Fire Protection Plan and fuel modification plans, establishing minimum evacuation standards and ingress/egress requirements, and minimizing impacts to biological resources. • Consider a Transfer of Development Rights program to move development potential from the SOI into lower risk areas.
• Limit the extension of public services and utility infrastructure into the City’s SOI (water, sewer, roadways) to reduce increasing fire risks and minimize other environmental impacts. A vast majority of wildfires are caused by humans and are started in close proximity to roadways, including the 2008 Freeway Complex City of Brea
September 24, 2025

Fire1, which started adjacent to State Route 91 with a faulty catalytic converter, and the 2017 Canyon Fire 22
, which started adjacent to State Route 91 and
Gypsum Canyon Road. Hills For Everyone has created a map of Fire Ignitions Near Chino Hills State Park (Exhibit C), which confirms that fire ignition clusters along SR-91, SR-57 and Carbon Canyon Road. Most significantly, Valencia Avenue should not be extended beyond the Olinda Alpha Landfill, and any expansion or extension to Tonner Canyon Road should not be built. Brea Canyon Road and Carbon Canyon Road should not be widened beyond their existing widths.
• Adopting the Puente-Chino Hills Wildlife Corridor Map (Exhibit A) as a basis to identify key locations where wildlife habitat corridors and safe roadway crossings should be created, enhanced, and protected from the impacts of development.

Establish Fire-Safe and Wildlife-Protective Standards for Development on the City’s Urban Edge. General Plan programs and policies should include:
• Require multiple evacuation routes for new development. • Establish standard conditions of approval (or establish and apply a Wildlife Overlay Zoning) to subdivision/zoning approvals to require measures that will help maintain connectivity and permeability for wildlife movement., There are many useful measures that should be adopted, including:
o Cluster development, including building pads and driveways, to minimize the perimeter edge of the neighborhood. Require the remainder of the parcel to be protected in an open-space/conservation easement that connects to off-site open space; no fences, structures, night lighting, or turf within the easement area;
o Dark-Sky Lighting. Full cutoff, motion-activated where feasible; 0.1 footcandle maximum at the open space border.
o Bird-Safe Design. For façades within 300 ft of open space, treat at least 90% of glazing with patterns, and prohibit reflective glass. o Mechanical Noise. Locate HVAC/pool equipment away from open space and enforce a maximum noise volume of 45 dBA at the property line. o Barriers and Fencing:
1 https://en.wikipedia.org/wiki/Freeway_Complex_Fire
2 https://en.wikipedia.org/wiki/Canyon_Fire_2
City of Brea
September 24, 2025

 Require a minimum of 50% permeable fencing (no continuous solid walls) with a minimum of 6 inches of ground clearance.
 Restrict grading/retaining walls that block known wildlife corridors. o Fuel Modification Plans need to be Wildlife-Permeable. Wildfire-safe fuel modification zones must maintain visual cover (allow patches 2-3 feet in height) and avoid complete denudation.
o When resurfacing or replacing culverts within known wildlife corridors or habitat linkages, upgrade to wildlife-passable crossings and add guiding fencing and native vegetation.

Update the General Plan to Comply with Assembly Bill 1889 and Senate Bill 1425.

These bills focus on habitat and connectivity needs for wildlife movement. General Plan program and policy priorities should include:
• Include mapped habitat corridors and wildlife linkages in the General Plan. The Puente-Chino Hills Wildlife Corridor Map (Exhibit B) contains some of this mitigation. Hills For Everyone, and other conservation organizations, can share additional maps and context.
• Ensure compliance with AB 1889. This bill requires the General Plan to consider the effect of development on the movement of wildlife and habitat connectivity.

The bill requires adoption of a wildlife connectivity element, or related goals, policies etc. in other elements. The updated General Plan shall, among other things, identify and analyze connectivity areas, permeability, and natural landscape areas within the jurisdiction, identify and analyze existing or planned wildlife passage features, and consider the impacts of development and the barriers caused by development to wildlife, as defined, and habitat connectivity.

Because Brea is embarking on a comprehensive GP Update, this is the appropriate time to comply with this important requirement, and developing a stand-alone Wildlife Connectivity Element for the General Plan would be the most comprehensive approach. Government Code Section 65302(i) also requires the City to incorporate information from a state plan on wildlife connectivity and best available science. The General Plan should incorporate recommendations from scientific sources, including a report written by Dr. Wayne Spencer at the Conservation Biology Institute: “Maintaining Ecological Connectivity Across the Missing Middle of the Puente-Chino Hills Corridor.” Dr. Spencer’s report builds on several previous ecological and wildlife movement studies in the Puente-Chino Hills, as well as the general literature on wildlife movement corridors where it applies to this valuable corridor. The report is included as Exhibit D to this letter.

City of Brea
September 24, 2025

• Ensure compliance with SB 1425. This bill mandates that the General Plan includes plans and action programs that address: 1) Equitable access to open space, considering social, economic, and racial equity; 2) Climate resilience and other benefits coordinated with the safety element; and 3) Rewilding opportunities to preserve and enhance natural ecosystems. Specific policies could include:
o Park Equity & Proximity. Ensure that at least 90% of residents live within a 10-minute walk (½ mile) of a park or publicly accessible open space, prioritizing disadvantaged or under-served neighborhoods. o Inclusive Design & Programming. Require universal design, multilingual wayfinding, shade/heat relief, and fee-free programming in communities with the greatest park gaps.
o Safe Access Corridors. Designate “Green Access Corridors” (bike/ped routes, greenways, creek trails) that connect disadvantaged or under-served neighborhoods to parks, schools, transit, and job centers. o No Net Loss of Community Open Space. In addition to identifying additional public open space in the City’s denser areas as development intensifies, prohibit conversion of parks/open space serving disadvantaged or under-served neighborhoods without replacement of equal or better quality/access.
o Nature-Based Risk Reduction. Prioritize nature-based solutions (floodplain reconnection, wetland/creek restoration, urban tree canopy, cool pavements) to minimize/mitigate flood, heat, wildfire, and drought risks.

These policies can also be cross-referenced to the Safety Element. o Rewilding Priority Areas. Designate a mapped “Rewilding Overlay” identifying core habitat, opportunity nodes (under-utilized parcels, flood channels, utility corridors), and connectivity linkages. o Native Plants First. Specify locally native, drought-tolerant plant palettes; prohibit invasive species in public landscapes; encourage reintroduction of keystone/native pollinator habitats where feasible.

Support Urban Greening and Climate Resilience. Preserve street trees, grow the urban forest, and mitigate the effects of peak season heat. General Plan programs and policies should include:
• Support the Urban Canopy. Establish an inventory-based citywide street-tree lifecycle program with the following elements:

City of Brea
September 24, 2025

o Prune street trees on a 3–5 year cycle and reserves annual funds for removal/succession planting with the goal of a “No Net Loss” urban canopy standard.
o Establish a citywide tree canopy target. The target measurement should be set to be a measurable improvement over existing conditions and should establish annual planting quotas to meet the target.
o Prioritize street tree planting in the City’s two census tracts that contain Disadvantaged Communities (as identified by CalEnviroScreen), with annual Council reporting.
• No Net Loss of Street Trees. Require tree replacement ratios of greater than 1:1 for both public and private property tree removals.
• Reduce Heat Gain. Adopt Cool Pavement standards and pair pavement resurfacing with shade tree/street tree planting quotas per linear mile. (The U.S.

Environmental Protection Agency publishes community guidance for cool pavement standards.3
)
• Cooling Urban Areas. Adopt a Heat and Air Quality Improvement Plan that contains:
o Cooling networks with shaded routes and designated cooling centers. o Subsidies or incentives for cool walls and cool roof retrofits. o Methods to integrate metrics for minimizing heat impacts into capital improvement programming.

IV. Conclusion
The proposed GPU and BCSP is an enormous opportunity for Brea’s community.

The development envisioned in the GPU and BCSP is likely to have significant environmental impacts, and it is essential that the EIR rigorously and comprehensively assess the Project. The City’s EIR must provide detailed analysis of the Project’s environmental impacts, evaluate alternatives to the proposed Project, and consider any and all potentially feasible mitigation measures to lessen or avoid the Project’s significant impacts. Implementing the policy and program suggestions in this letter should be beneficial to the GPU and BCSP EIR.
3 https://www.epa.gov/heatislands/using-cool-pavements-reduce-heat-islands City of Brea
September 24, 2025

Please notify Hills For Everyone and this office of the release of the Draft GPU/BCSP and the Draft EIR, and provide us all notices for any hearings, staff reports, briefings, meetings, and other events related to the Project.

Respectfully yours,

SHUTE, MIHALY & WEINBERGER LLP
Kristi T. Bascom, AICP
Urban Planner
cc: Claire Schlotterbeck, Hills For Everyone
Edward Schexnayder, Attorney, Shute, Mihaly & Weinberger, LLP Exhibits:

A: Puente-Chino Hills Wildlife Corridor Map, prepared by Hills For Everyone B: Public Agency Investment Table, prepared by Hills For Everyone C: Fire Ignitions Near Chino Hills State Park, prepared by Hills For Everyone D: Maintaining Ecological Connectivity Across the “Missing Middle” of the PuenteChino Hills Wildlife Corridor, prepared by Dr. Wayne D. Spencer of the Conservation Biology Institute (2005)
1970728.5
Exhibit A

Exhibit B
State and Federal Agencies
U.S. Army Corps of Engineers N/A 124 $0 $1,850,000
1982-'98 11,770 $62,169,274 $62,443,972
2005-2006* 1,594 $0 $6,420,000
California Department of Parks and Recreation and
US Fish and Wildlife Service 2000-2001 685 $53,500,000 $63,500,000 California Department of Parks and Recreation Restoration TBD TBD TBD Regional Agencies
Los Angeles County Department of Parks and
Recreation 1960-'80 583 $3,735,000 $7,000,000
Los Angeles County Department of Public Works N/A 35 $0 $700,000 Los Angeles County Sanitation Districts* N/A 225 $0 $2,700,000 2011 301 $2,960,000 $2,960,000
Restoration 27 $440,500 $440,500
Orange County Parks N/A 729 $0 $14,580,000
Local Agencies
City of Chino Hills 1990 - 2022 3,000 $20,000,000 $20,000,000 City of Brea* Tonner Hills CE TBD TBD TBD
City of Yorba Linda* N/A 170 $0 $2,550,000
City of Whittier 1994 - 2007 1,756 $15,086,500 $15,336,500 Joint Powers Authority
1996-2022 3,886 $32,726,028 $35,760,000
Restoration 37 $4,500,000 $4,500,000
Tres Hermanos Conservation Authority** 2019 2,445 $24,450,000 $24,450,000 1997 200 $2,250,000 $2,250,000
2019 40 TBD TBD
2020-2021 400 $3,160,000 $3,160,000
2021 320 $2,560,000 $2,560,000
2021 9 $165,000 $165,000
Private Entities & Non-Profits
Rivers and Lands Conservancy 2021 300 TBD TBD
28,572 $222,761,802 $232,625,472
TOTAL RESTORED ACREAGE: 64 $4,940,500 $4,940,500
$227,702,302 $237,565,972
* Property dedicated for free as public open space as a result of the regulatory process. ** Property has no legal conservation mechanism
TOTAL INVESTMENT:

TOTAL ACQUIRED ACREAGE:

Public Agency Acquisition Investments in the Puente-Chino Hills Wildlife Corridor Estimated Current Value
of Properties
Actual Public
Investment
Total
Acreage
Acquisition
Date(s) Public Agency Landowner
California Department of Parks and Recreation
Orange County Transportation Authority
Puente Hills Habitat Preservation Authority
Mountains Recreation and Conservation Authority
Exhibit C
µ
Fire Ignitions Near Chino Hills State Park (1914-2018)
Data Provided by CalFire, Chino Hills State Park, Chino Valley Fire District and City of Brea.

Last Updated September 2019
Projection: Lambert Conformal Conic
Datum: North American 1983
Scale: 1: 60,000
10 6
Senate District 29
0 0.5 1 2 3 4
µ
Miles
LEGEND
County Boundaries
Chino Hills State Park
Study Area
Known Cause
Unknown Cause
Exhibit D
Maintaining Ecological Connectivity
Across the “Missing Middle”
of the
Puente-Chino Hills Wildlife Corridor
Final Report
July 2005
The Conservation Biology Institute provides scientific expertise to support conservation and recovery of biological diversity in its natural state through applied research, education, planning, and community service.

Maintaining Ecological Connectivity
Across the “Missing Middle”
of the
Puente-Chino Hills Wildlife Corridor
Final Report
Prepared by:

Wayne D. Spencer, Ph.D.
815 Madison Avenue
San Diego, CA 92116
Prepared for:

Resources Legacy Fund Foundation
555 Capitol Mall, Suite 650
Sacramento, CA 95814
July 2005
Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute ii July 2005
Table of Contents
Page
Acknowledgements ................................................................................................................ iv Executive Summary.................................................................................................................v Methods................................................................................................................................v Results............................................................................................................................... vii Discussion.......................................................................................................................... ix Conclusions and Recommendations ....................................................................................x Introduction..............................................................................................................................1 Report Objectives.................................................................................................................2 Study Area ................................................................................................................................4 Biogeography.......................................................................................................................4 Previous Studies...................................................................................................................4 Methods...................................................................................................................................10 Reconnaissance..................................................................................................................10 Target Species....................................................................................................................11 Defining Geographic Units, Barriers, and Filters ..............................................................14 Analyses — Assessing Existing and Future Functionality................................................18 Results .....................................................................................................................................20 Functionality of Geographic Units.....................................................................................20 Summary of Overall Corridor Function.............................................................................31 Future Corridor Functions..................................................................................................35 Discussion................................................................................................................................40 Functions and Benefits of Wildlife Corridors....................................................................40 Assessing Connectivity Pros and Cons..............................................................................40 Mitigating Road Effects.....................................................................................................43 Conclusions and Recommendations.....................................................................................45 Conservation and Restoration Priorities for the Missing Middle ......................................45 References Cited.....................................................................................................................49 Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute iii July 2005
Page
Maps
Map 1. Study area showing the Missing Middle of the Puente-Chino Hills Wildlife Corridor................................................................................................3 Map 2. Geographic units of the Puente-Chino Hills Wildlife Corridor……………... 15 Map 3. Conservation and restoration priorities in the vicinity of Missing Middle...... 46 Figures
Figure 1. The Puente-Chino range of hills juts into the heavily urbanized Los Angeles Basin from the tip of the Santa Ana Mountains range……………………...… 1 Figure 2. View northwest across Coal Canyon Wildlife Underpass…......................... 23 Figure 3. View northeast across Tonner Bridge and Highway 57…………………….. 25 Figure 4. View northwest across Segment 3 and Harbor Boulevard to Segment 4, indicating general trends in wildlife movements……………………………. 27 Figure 5. Conceptual development plan for the Shell-Aera Master Planned Community………………………………………………………………… 35
Figure 6. Aerial photograph showing City of Industry’s proposed Tres Hermanos reservoir and new road in Tonner Canyon…………………………………... 37 Photos
Photo 1. View east under the Tonner Bridge…………………………………………. 26 Photo 2. View southeast across the Harbor Boulevard “deathtrap”…………………. 28 Tables
Table 1. Summary of previous studies of wildlife populations and movements in the Puente-Chino Hills study area………………………………………………... 5
Table 2. Characteristics of geographic units comprising the Puente-Chino Hills Wildlife Corridor……………………………………………………………. 21
Table 3. Characteristics of roads crossing the Puente-Chino Hills Wildlife Corridor... 22 Table 4. Functional classification of geographic units for supporting target species populations and movements…………………………………………………. 33
Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute iv July 2005
Acknowledgements
Conservation Biology Institute (CBI) thanks the following individuals and organizations for support and contributions to this report. Financial support was provided by Resources Legacy Fund Foundation, with special thanks to Maureen Rose and Ed Hastey. Rick Rayburn (California State Parks) was responsible for involving CBI in this important project and provided early guidance on its goals. Claire Schlotterbeck (Hills For Everyone) provided essential information, advice, contact information, and inspiration, and Melanie Schlotterbeck (The Trust for Public Land) provided GIS data, photographs, advice, information, contacts and other valuable input. Dan Wooldridge (Waters and Faubel) provided copies of various reports and plans reviewed in this report. Andrea Gullo and Amy Henderson (Puente Hills Landfill Native Habitat Preservation Authority) also provided data, reports, and other useful information. Geary Hund, Claire Schlotterbeck, Melanie Schlotterbeck, and Amy Henderson reviewed a draft of this report and offered valuable corrections and clarifications to the contents. The following CBI employees assisted in preparing this report: Heather Rustigian, with oversight from Jim Strittholt, prepared GIS maps and calculations; John Bergquist provided Keyhole screen captures used as illustrations; and Mike White and Jerre Stallcup reviewed and helped produce the report.

Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute v July 2005
Executive Summary
The Puente-Chino Hills Wildlife Corridor is a peninsula of mostly undeveloped hills jutting about 42 km (26 miles) from the Santa Ana Mountains into the heart of the densely urbanized Los Angeles Basin. Intense public interest in conserving open space here has created a series of reserves and parks along most of the corridor’s length, but significant gaps in protection remain.

These natural habitat areas support a surprising diversity of native wildlife, from mountain lions and mule deer to walnut groves, roadrunners, and horned lizards. But maintaining this diversity of life requires maintaining functional connections along the entire length of the corridor, so that wildlife can move between reserves—from one end of the hills to the other.

Already the corridor is fragmented by development and crossed by numerous busy roads, which create hazards and in some cases barriers to wildlife movement. Proposed developments threaten to further degrade or even sever the movement corridor, especially within its so-called “Missing Middle.” This mid-section of the corridor system, stretching from Tonner Canyon on the east to Harbor Boulevard on the west, includes several large properties proposed for new housing, roads, golf courses, and reservoirs. Such developments would reduce habitat area and the capacity to support area-dependent species and, if poorly designed, could block wildlife movement through the corridor.

This report builds on an impressive array of previous ecological and wildlife movement studies in the Puente-Chino Hills, as well as the general literature on wildlife movement corridors as it applies to this unique peninsula of wildness. It supplements the existing information with an analysis of gaps in protection—with special focus on the vulnerable Missing Middle—and recommends conservation and management actions to prevent further loss of ecological connectivity and retain native species.

Methods
I performed a meta-analysis of corridor function using existing scientific information on the distribution and movement patterns of wildlife species in the study area, as supplemented by field reconnaissance and examination of aerial and satellite imagery. Following the lead of previous researchers, I segmented the range of hills into nine geographic units by roads and other breaks in habitat contiguity. From southeast to northwest these are:
• A biological “core” area (defined below), represented by the Santa Ana Mountains; • Seven segments of the functional Puente-Chino Hills Wildlife Corridor (from southeast to northwest: 1-Chino, 2-Carbon-Tonner, 3-Shell-Aera, 4-Powder-Schabarum, 5-San Miguel, 6-East Whittier, 7-West Whittier); and
• One isolated patch off the tip of the range of hills (Whittier Narrows), which is effectively disconnected from the functional corridor segments by major roads and urban barriers.

Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute vi July 2005
The Missing Middle consists of the western portion of Segment 2 (including the large and biologically diverse Tonner Canyon) and all of Segment 3 (Shell-Aera property and adjacent lands between Highway 57 and Harbor Boulevard). The eastern portion of Segment 2 (between Tonner and Carbon Canyons) is largely conserved already, but Tonner Canyon and Shell-Aera are unprotected and threatened by development projects.

Each of the nine geographic units was initially characterized for how it appears to function in supporting populations of target species, including mountain lion, mule deer, bobcat, coyote, coast horned lizard, and greater roadrunner, as well as in the richness of its reptile and amphibian community. The following coarse-scale definitions apply to these units:
• Core areas must be larger than 2,000 sq. km and capable of supporting a population of 20 adult mountain lions (the most area-dependent target species). Due to large size and relatively low “edge effects,” a core area will support the greatest diversity of species and should support populations of all target species. The Santa Ana Mountains are the only core in the study area. This core serves as a source for mountain lions and other species to enter the corridor system.
• Subcores are smaller (but at least 60 sq. km) and capable of supporting a population of bobcats, the second-most area-dependent target species. Subcores can sustain populations of most target species and have moderate to high species diversity. Corridor Segment 1 (Chino Hills between Highways 91 and 142) is the only subcore, although Segment 2 appears to function as an extension of this subcore, as discussed below. • Patches are smaller than 60 sq. km, but may support small numbers of bobcats and significant populations of other target species. Patches may also provide significant livein or move-through habitat for mountain lions and bobcats, whose home ranges may cover multiple geographic units. Most segments in the corridor system are patches, but they vary greatly in size (from about 1.5 to 44.3 sq. km), vegetation composition, isolation by roads, and ability to support target species.

The roads delimiting these segments were next characterized for their effects on target species movements—as barriers, semi-permeable “filters,” or highly permeable filters. Based on the scientific literature and field reconnaissance, each road was assessed for how easily target species can cross it, the availability and effectiveness of crossing structures (e.g., bridges and underpasses), and relative frequency of roadkill. Roads considered highly permeable to wildlife movement allow adjacent segments to function as one larger segment, such that two areas originally classified as separate patches may effectively serve as one larger patch (summing the area of adjacent units), or even a subcore, for certain target species.

I assigned each newly defined unit, or composite unit, a function relative to supporting individuals or populations of each target species based on unit size, habitat composition, and other factors, as follows:

Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute vii July 2005
• Population — capable of supporting a breeding population of at least 20 adults and potentially serving as a source of individuals that disperse into other units. • Subpopulation — capable of supporting at least two but less than 20 breeding individuals.

Subpopulations may exchange individuals with other areas within a larger metapopulation (a set of partially isolated populations linked by occasional dispersal) and may provide individuals to recolonize habitat patches in case of local extirpation. • Home Range Part — incapable of supporting at least two breeding individuals on its own, but may provide live-in habitat (e.g., foraging or resting cover) and form a part of one or more individuals’ home range(s).
• Move-through — not contributing significant live-in habitat for a species as part of a functional home range, but capable of accommodating movements between more substantial units within a home range, or potentially used for dispersal between other habitat units.

This system for characterizing geographic units and movement impediments was used to assess how the overall corridor system functions to support target species, and how these functions might change with potential development scenarios, such as new roads or housing that could add movement barriers or reduce wildlife carrying capacity in corridor segments.

Results
Existing Corridor Function
The Puente-Chino Hills Wildlife Corridor appears functional for at least larger mammals and birds, although tenuously so in the Missing Middle (due to several barrier or near barrier roads) and across smaller Segments 4 and 5 (due to their small size, strong edge effects, and high human and pet activity). Essentially all roads in the study area are considered barriers or at least strong filters to movements by many reptiles, amphibians, and small mammals; however, most birds and larger mammals currently can move between all segments either at-grade (with mortality risks) or via critical road-crossing structures. Despite many crossing constraints through the corridor, especially in and just west of the Missing Middle, target species are confirmed or highly likely to occur in all seven Puente-Chino Hills corridor segments, except for coast horned lizard, which may already be absent (or will disappear in the future) west of Highway 57.

Individual mountain lions are capable of traversing the length of the corridor, albeit at some risk of roadkill, and one or more lions still hunt as far west as the western Puente Hills (known locally as the Whittier Hills). Most other target species (e.g., bobcats, roadrunners) appear to persist throughout the corridor as metapopulations that are connected genetically and demographically by at least occasional dispersal between geographic units.

Carbon Canyon Road (between Segments 1 and 2) and Turnbull Canyon Road (between Segments 6 and 7) are considered highly permeable to at least larger mammals and birds, so I Puente-Chino “Missing Middle” Analysis
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merged Segments 1 and 2 to form a larger Chino-Tonner subcore, and I merged Segments 6 and 7 to form a larger Whittier Hills patch. The most critical road-crossing structures are the Coal Canyon Wildlife Underpass (connecting the Santa Ana Mountains Core to the Chino Hills under Highway 91); a box culvert under Carbon Canyon Road known to be used by bobcat and other species; the Tonner Canyon Bridge on Highway 57 (the only viable crossing beneath this busy freeway for deer, mountain lion, bobcat, and other species); and the Colima Service Tunnel (used by bobcat, deer, coyote, and other species to cross under Colima Road between San Miguel Canyon and the Whittier Hills). In addition, a new wildlife tunnel is being built under Harbor Boulevard (between Segments 3 and 4) at a location well-documented as a roadkill “death trap.” There appears to be a gradient of declining amphibian and reptile diversity and evenness moving west from the Chino Hills, probably due to increasing edge effects coupled with increasing distance and number of barriers and filters that must be crossed the farther west one moves from source habitats in the east. A similar gradient may exist for other taxa, such as small mammals, that are similarly limited in their dispersal abilities.

Given the length of the corridor relative to species movement abilities, the capacity of corridor segments to support many species depends both on
• The potential for individual movement between each set of adjoining segments (a function of roads and road-crossings), and
• Having sufficient live-in habitat along the way to support populations or subpopulations that contribute dispersing individuals.

The greater a segment’s distance from units supporting populations or subpopulations of a species, the lower the probability that the segment can continue supporting a species. If the distance between occupied segments becomes too great, or if barriers prevent inter-segment movement, local extinctions are inevitable in the isolated segments. Thus, any reduction in the capacity of segments to support populations or subpopulations increases the probability of local extinctions in that segment, as well as in all other “downstream” segments to the west.

Habitats in the Missing Middle are critical to maintaining overall corridor function. The Tonner Canyon area serves as an extension of the large Chino-Tonner subcore, with significant live-in habitat that can contribute dispersing animals to move into other segments. Likewise, Segment 3 (Shell-Aera) presumably supports significant numbers of target species that disperse (currently at some risk) across Harbor Boulevard into Powder Canyon (Segment 4) and beyond.

Future Scenarios
I assessed the likely effects of several proposed development projects in the Missing Middle on species persistence through the corridor system. This qualitative assessment uses the conceptual model developed above, based on how projects might affect the capacity of geographic units to support populations or individuals and the ability of individuals to cross between units. The projects include a new residential community, a series of reservoirs, and a major new road.

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All three proposed developments have the potential to extirpate target species from large portions of the Puente-Chino Hills Wildlife Corridor. By impeding species movements or metapopulation dynamics, a project’s impacts on species persistence may extend far beyond project boundaries, potentially rippling through the range of hills to eliminate wildlife populations as far west as the Whittier Hills (10-12 km west of the Missing Middle). The proposed Shell-Aera Master Planned Community would seriously degrade the ability of Segment 3, and all segments farther west, to support target species, especially mountain lion and bobcat.

This would have cascading effects on flora and fauna in all segments from this point west.

A plan by the City of Industry to build three water reservoirs in Tonner Canyon could also have substantial adverse impacts on corridor function. Although a reservoir or other development in upper reaches of Tonner Canyon might not greatly affect corridor function, any development in middle and especially lower Tonner Canyon could have severe impacts on corridor function, especially if wildlife use of the Tonner Canyon Bridge (to cross Highway 57) is reduced. Any development that blocks access through the bridge area would make Highway 57 a complete barrier to many species and would likely lead to wildlife extirpations in segments farther west.

At the very least, creation of these reservoirs would reduce the size of the Chino-Tonner subcore and its capacity as a source of animals that disperse into the rest of the corridor system.

Finally, plans by the City of Industry to build a new road running the length of Tonner Canyon could split the Chino-Tonner subcore in two, potentially isolating about 21.2 sq. km of habitat from this currently large and contiguous source habitat. The road would probably require major cut and fill to construct and could render disfunctional the critical Tonner Bridge wildlife undercrossing. This would almost surely result in the rapid loss of mountain lion and bobcat from more westerly segments, with cascading effects through the ecological community. Deer and other species would also likely disappear from westerly segments over a longer time period.

A full impact analysis for any of these proposed projects should address cumulative impacts on wildlife populations and movements through the corridor. Among these cumulative impacts would be inducement of further development, such as additional residential, commercial, or industrial development along the road. Increases in traffic and roadkill should also be analyzed and mitigated for. Any combination of two or more of these projects, even if well designed, would likely render the Puente-Chino Hills Wildlife Corridor non-functional west of Chino Hills State Park, regardless of mitigation.

Discussion
The scientific literature on the functions and values of wildlife corridors is huge and growing.

Movement corridors connecting reserves or larger “core areas” of habitat have been documented to counter many adverse effects of isolation by fragmentation on species and ecological processes. Some critics have argued that there are costs as well as benefits to conserving corridors and that, under certain circumstances, creating or maintaining corridors could harm some species or communities. However, the overwhelming weight of scientific evidence is that maintaining connectivity is beneficial, especially for those species and ecological communities Puente-Chino “Missing Middle” Analysis
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for which connectivity “is the natural state of things.” Most arguments against corridors boil down to nothing more than cautions against viewing them as conservation panaceas.

Nevertheless, I reviewed the following arguments made against corridor conservation as they apply to the Puente-Chino Hills Wildlife Corridor:

1. Corridors may serve as conduits for the spread of deleterious species;

2. Corridors may spread detrimental processes, such as wildfire or disease, among reserve areas;

3. Corridors may facilitate movements by highly mobile and adaptable animals (like coyotes), but may not help more sedentary or at-risk species;

4. Corridors could attract wildlife into edge-affected habitats with high mortality rates; and

5. Corridor conservation may be more expensive or less beneficial than other options, such as increasing the size or management of core reserves.

Critical review of these concerns for the Puente-Chino Hills Wildlife Corridor finds them irrelevant or insignificant in this case; at least, the biodiversity benefits of conserving the corridor far outweigh any potential for harm.

Mitigating the adverse effects of roads, including barrier effects and increased mortality, is essential to maintaining corridor functions. The scientific literature on effective mitigation actions, especially wildlife road-crossing structures, is also large and growing, with many success stories. The main types of structures, from most to least effective, are vegetated landbridges (wildlife overpasses), bridges, underpasses, and culverts. Vegetated overpasses are quieter than underpasses, maintain ambient conditions, seem less intimidating for some species than dark tunnels, and have proven highly successful in the U.S., Canada, and Europe for a wide variety of wildlife species. Bridges are also highly effective, especially if wide and open with natural vegetation growing beneath, such as under the Tonner Bridge. Culverts and other tunnellike structures can be effective for some species, but only very large culverts (such as box culverts and equestrian tunnels) are effective for larger mammals. Earthen flooring is preferable to concrete or metal. Regardless of crossing type, wildlife fencing is crucial for keeping animals off the road and for funneling them toward the crossing structure. Vegetative cover near the entrances also increases wildlife use of crossing structures.

Conclusions and Recommendations
Given the huge investment already made to maintain the Puente-Chino Hills Wildlife Corridor, additional conservation investment in the Missing Middle seems not only prudent, but essential if society believes the continued presence of deer, bobcats, roadrunners, and other wildlife is desirable in this unique peninsula of wild in a sea of development. My recommendations for how to do this are largely concordant with previous recommendations by other biologists.

I recommend conserving all of Segment 3 (the Shell-Aera property) and at least the middle and lower portions of Tonner Canyon, including prohibiting any new road or other development that Puente-Chino “Missing Middle” Analysis
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would fragment this critical habitat block or degrade in any way the utility of the Tonner Bridge as a wildlife underpass. I also emphasize the following recommendations for improving roadcrossing structures and reducing roadkill.

A. Add wildlife fencing on either side of Carbon Canyon Road to reduce roadkill and encourage wildlife to use existing culverts, especially the concrete box culvert near the entrance to Chino Hills State Park. Add another wildlife crossing structure (bridge or vegetated over-crossing), designed to accommodate all large mammals, as mitigation for any future road upgrades.

B. Prohibit any development that would increase traffic under the Tonner Bridge or add any new impediments (structures, lights, noise, etc.) to the vicinity of the bridge. Restore riparian vegetation along Tonner Creek, where degraded by oil development activities.

Fence along Highway 57 if monitoring suggests road mortality is high.

C. Secure rights to install wildlife fencing along both sides of Harbor Boulevard to reduce roadkill and ensure maximum utility of the wildlife tunnel being built here. Plant screening vegetation on either side of the tunnel to provide cover to wildlife approaching the entrances.

D. Secure remaining “at-risk” parcels in the narrow, constricted portion of the corridor between Powder Canyon and Hacienda Boulevard. Enlarge or otherwise improve the existing equestrian tunnel under Hacienda Boulevard to enhance its use by wildlife, including adding screening vegetation on the western end. Add wing fencing on either side of the tunnel to help funnel wildlife to it. Do not fence extensively along Hacienda Boulevard, unless coupled with new crossing structures, because most large mammals currently cross at-grade. Consider building a wildlife overpass (a vegetated wildlife bridge) over Hacienda Boulevard, taking advantage of steep slopes rising up from either side of the road, as mitigation for any future road improvements that would increase traffic volume or speed.

E. Maintain and improve the Colima Service Tunnel as a critical wildlife underpass. Add fencing or screening vegetation if necessary, based on further site-specific inspection or monitoring. Limit actions that would increase disturbance in the vicinity of the Service Tunnel from sunset to sunrise, such as artificial lighting or nighttime traffic or recreational uses through the tunnel.

Puente-Chino “Missing Middle” Analysis
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Figure 1. The Puente-Chino range of hills juts into the heavily urbanized Los Angeles Basin from the tip of the Santa Ana Mountains range (Keyhole screenshot).

Introduction
The Chino and Puente Hills form a peninsula of wild uplands that jut from the Santa Ana Mountains into the heart of one of the largest unbroken urban areas in North America (Figure 1).

Created by shifting Earth plates, this peninsula of wild in a sea of development supports a surprising diversity of native wildlife. Mountain lions still hunt mule deer in the area’s diverse mosaic of grasslands, chaparral, coastal sage, and oak and walnut woodlands; roadrunners, California gnatcatchers, northern harriers, and other birds in decline throughout Southern California still persist here; as does a remarkably rich reptile and amphibian fauna.

Maintaining this diversity, and the web of healthy ecological interactions it represents, presumably requires keeping this range of hills fully connected by wild habitats along its 42 km (26 mi) length. Severing connections or blocking movement along this corridor with roads or housing projects threatens to extirpate species from this urban reserve system and degrade ecological health throughout this range of hills—thus eliminating a remarkable ecological classroom within easy reach of millions of people craving a connection with nature.

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This loss would be doubly unfortunate given the tremendous public investment already made to conserve and restore biological open space and unfettered wildlife movement through this range of hills—from the Coal Canyon wildlife underpass at Highway 91, through Chino Hills State Park, Powder Canyon, Schabarum Park, and other private and public open space dedications to the western end of the Puente Hills (known locally as the Whittier Hills1). According to the California Department of Parks and Recreation, nearly a quarter billion dollars have already been expended or committed to acquiring and restoring natural open space in the Puente-Chino Hills Wildlife Corridor (http://hillsforeveryone.org/state_investment_table.htm). But the benefits of these existing investments is severely threatened by proposed development projects— including new roads, housing developments, golf courses, and reservoirs.

These threats are most urgent in the so-called “Missing Middle” of the corridor—from Tonner Canyon on the east (mostly owned by the City of Industry) to Harbor Boulevard on the west (Map 1). No major reserves are yet established in this broad midsection of the Puente-Chino Hills, and connectivity is threatened by a major new housing development, a proposed road, and a series of new dams and reservoirs that would flood Tonner Canyon. Should one or more of these projects sever functional connectivity, reserves farther west (e.g., Habitat Authority Wilderness Preserve, Powder Canyon, and Schabarum Regional Park, among others) could lose key species and suffer further ecological degradation.

This report reviews available scientific evidence on wildlife movement corridors, reserve design, and local biological resources to define conservation priorities for maintaining connectivity from one end of the corridor to the other. It focuses on the Missing Middle, because this portion is least protected and is at most immediate risk of further degradation. The purpose of this analysis is to identify (a) those portions of the Missing Middle whose conservation would most contribute to continued wildlife movement and ecosystem health throughout the corridor system, and (b) remedial actions that would most improve the situation for native wildlife—such as retrofitting existing roads with wildlife crossing structures to reduce roadkill and improve movement opportunities.

Report Objectives
• Synthesize the science of wildlife movement corridors as it pertains to the Puente-Chino Hills Wildlife Corridor.
• Analyze existing conditions and potential future conditions for the persistence and movement of wildlife populations in the corridor system. • Recommend conservation and management priorities to sustain and improve connectivity through the Missing Middle and hence the greater Puente-Chino Hills Wildlife Corridor.

1 Although “Whittier Hills” is not an official geographic name recognized by the U.S. Geological Survey, the western portion of the Puente Hills is known locally as the Whittier Hills, and previous researchers have used this place name. I therefore also use Whittier Hills to refer to the hills west of Colima Boulevard.

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Map 1. Study area showing the Missing Middle of the Puente-Chino Hills Wildlife Corridor.

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Study Area
This study considers two nested study areas (Map 1): the entire Puente Hills-Chino Hills Wildlife Corridor, extending about 42 km from the Santa Ana Mountains to the San Gabriel River, and the so-called “Missing Middle” of this larger landscape. The Missing Middle is that section of the Puente-Chino Hills Wildlife Corridor from Harbor Boulevard on the west to and including Tonner Canyon on the east. The Missing Middle is largely unconserved and is threatened by a variety of development projects.

Biogeography
The Puente-Chino Hills are the northernmost extension of the Peninsular Mountain Range, which begins in Baja California, Mexico. They are a topographic expression of the 500-km-long Whittier-Elsinore fault system, pushed up between the Whittier and Chino sections of this major slip-shear fault system. The geologically dramatic origins of the hills also contribute to their relatively undeveloped status, because steep slopes, earthquakes, landslides, tar pits, and active and former oil wells have tended to limit development, at least until recently.

The hills rise from the flat Los Angeles Basin, at less than 100 m (300 ft) elevation, to over 540 m (nearly 1,800 ft) at San Juan Hill. The regional climate is mild and Mediterranean, which contributes to the high diversity of species in coastal Southern California. Vegetation in the hills is a mosaic of open grasslands (which have been affected by grazing over the years), coastal sage scrub, chaparral, oak woodlands, riparian scrub, riparian woodlands, and rare California black walnut woodlands—a grossly under-protected resource that could be considered an “endangered habitat.” These communities support flora and fauna relatively typical of the biodiversity in Southern California—which is remarkable given that the hills are entirely surrounded by the largest urbanized area in the U.S.

Previous Studies
The Puente-Chino Hills represent one of the most closely scrutinized and intensively researched wildlife movement corridors in Southern California, if not North America. Its existence and importance are well appreciated by the local populace, with 53% of local residents having “heard of the wildlife corridor in the Puente Chino Hills area” and 83% in favor of maintaining the corridor (51% “strongly” supported this) (Decision Research 2003). The area’s flora, fauna, and ecological functions are well studied, with a number of intensive studies of wildlife distributions and movements covering all or substantial portions of the area (Table 1). In 1994 an entire scientific conference was focused on the biological functions and values of this unique range of hills (Natural Resources in the Puente Hills-Chino Hills Corridor: Implications for Land Use and Planning. A symposium at Whittier College, March 18-19, 1994)2 .

2 Abstracts of papers presented at this conference can be found at http://www.hillsforeveryone.org/PDF_Files/whittier_college_symposium.pdf.

Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute 5 July 2005 Table 1. Summary of previous studies of wildlife populations and movements in the Puente-Chino Hills study area. Reference Target Species Major Focus Study Area Methods Relevant Results Recommendations Robertson et al. 1995 Large mammals
Assess likely movement routes and constraints.

Entire PuenteChino Hills Wildilfe Corridor from the Santa Ana River to the San Gabriel River.

Field reconnaissance, walking the length of the corridor to assess likely movement routes and constraints. Incidental observations of wildlife sign and roadkill.

At least one pathway without complete obstruction existed for large mammals, from the Santa Ana River to the Whittier Hills, in 1994-95, but with several significant constraints. The most critical impediment was Harbor Blvd. and adjacent development. Movement across Interstate 605 to the San Gabriel River (Whittier Narrows Recreation Area) considered “highly improbable.” Conserve land to connect existing reserves (especially in the middle portions of the Corridor); restore native vegetation; retrofit undercrossings at problem roads, especially Harbor Blvd., with tunnels or bridges to reduce roadkill and improve connectivity for large mammals.

Noss et al. 1997
All vertebrate wildlife
Assess importance of Coal Canyon linkage to maintaining viable species populations in the Santa Ana Mountains and Puente-Chino Hills.

Entire PuenteChino Hills Wildlife Corridor and Santa Ana Mountains.

Literature review, field reconnaissance, and analysis of which species’ populations were likely to benefit from protecting and improving the Coal Canyon linkage and underpass.

Coal Canyon is the last viable linkage between the Chino Hills and Santa Ana Mountains. At least 21 vertebrate species have populations <500 individuals in the Puente-Chino Hills, and at least four of these have <50 breeding adults. Risks of extirpation from the hills would increase for all these species in the absence of the Coal Canyon corridor. The corridor also benefits species in the Santa Ana Mountains, especially the mountain lion and several grassland species. Mountain lion and bobcat would likely be the first species adversely affected by loss of the corridor.

Protect and restore a functional undercrossing at the Coal Canyon interchange with Highway 91. Remove pavement and restore natural soils, vegetation, and drainage through the undercrossing, and install wildlife fencing to funnel wildlife off the highway and through the underpass.

Puente-Chino “Missing Middle” Analysis
Table 1. Continued. Conservation Biology Institute 6 July 2005 Reference Target Species Major Focus Study Area Methods Relevant Results Recommendations Haas and Crooks 1999, Haas 2000, Haas and Turschak 2002 Large and mediumbodied mammals
How landscape variables and underpass characteristics affect the distribution and relative abundance of target species in the study area, and the frequency of underpass usage by each species.

Entire PuenteChino Hills Wildlife Corridor, from Santa Ana River to Whittier Hills.

Field methods: scat transects, remote-triggered camera stations, and baited track stations. Statistical analyses:

Correlated probability and frequency of species use with landscape variables (e.g., corridor width, % wild) and underpass characteristics.

Bobcat and long-tailed weasel were negatively associated with habitat fragmentation. Fragmentation was negatively associated with probability of underpass usage by coyote, bobcat, and long-tailed weasel, and negatively associated with the frequency of use by bobcat. Underpass dimensions were important in determining probability of use by deer and gray fox, and with frequency of use in coyote, gray fox, deer, and domestic cat, with more open underpasses used most. The amount of natural cover surrounding the underpass entrance was important for bobcat. Fencing and roadway dividers were most effective on coyote use of underpasses. Overall, the probability of an underpass being used depends primarily on landscape characteristics,
while its frequency of use depends primarily on underpass dimensions.

Bobcats are an excellent target species for conservation in the study area. Habitat acquisition and restoration should be concentrated in the narrowest portion of the corridor and at chokepoints along roadways. Existing underpasses should be surrounded by natural cover and use fencing to direct wildlife under the roadway. Future underpasses should be large and situated as far from residential areas as possible.

Puente-Chino “Missing Middle” Analysis
Table 1. Continued. Conservation Biology Institute 7 July 2005 Reference Target Species Major Focus Study Area Methods Relevant Results Recommendations Cooper 2000 Breeding birds Determine distribution of breeding land birds to identify priority conservation areas.

Entire PuenteChino Hills Wildlife Corridor, from Santa Ana River to Whittier Hills.

Point counts and walking transects to determine presence/absence.

California gnatcatcher, cactus wren, and other rare or declining species documented in diverse locations. Greater roadrunner widespread but not common; most commonly observed in middle portions of the Corridor. California quail found throughout study area except smallest fragments. Burrowing owl apparently extirpated from the study area during the 1990s. Several areas of high-quality habitats supporting diverse avifauna identified.

Conserve three priority areas based on size, threats, and support of declining species: (a) coastal sage scrub in northern Brea and Yorba Linda (southern portion of Missing Middle); (b) extensive grassland and savannah south of Rowland Heights (northern portion of Missing Middle); (c) grasslands of upper Tonner Canyon (northeastern portion of Missing Middle).

PCR et al. 2000
General wildlife
Analyze the Puente Hills area as a Significant Ecological Area (SEA) recognized by the County of Los Angeles.

That portion of the study area within Los Angeles County, from the Whittier Narrows to Tonner Canyon.

No original field studies; review and analysis of existing information.

The area meets several designation criteria as an SEA, including that it is regionally important to many resident and migrating species, especially large mammals, wintering raptors, and songbirds, in large part due to regional connectivity.

Retain connectivity and linkage values between major canyons of the SEA, and especially at choke points and major road crossings.

Puente-Chino “Missing Middle” Analysis
Table 1. Continued. Conservation Biology Institute 8 July 2005 Reference Target Species Major Focus Study Area Methods Relevant Results Recommendations Lyren 2001 Coyotes and bobcats
Home range and movement characteristics, roadkill, and underpass use by bobcats and coyotes.

Primarily along SR 71 and adjoining areas occupied
by telemetered
animals.

Radio telemetry (29 coyotes, 4 bobcats); roadkill surveys along SR-71.

Home ranges of about half of all telemetered animals overlapped SR71, indicating frequent road crossing by individuals. Most animals crossing
the road were documented using underpasses; coyotes used underpasses more than bobcats. Coyote use of underpasses seemed suppressed by traffic volume. No bobcats were found road-killed; coyotes frequently were road-killed, with concentrations where no wildlife fencing was present along road.

Wildlife fencing should be used to funnel wildlife to underpasses.

Schlotterbeck 2001
Large and mediumbodied mammals; reptiles and amphibians.

Assemble existing data from Haas and Crooks 1999 and Case and Fisher 1998 into a GIS database.

Entire PuenteChino Hills Wildlife Corridor, from Santa Ana River to Whittier Hills.

No original field studies. Interviews with previous researchers and compilation and analysis of existing field data.

See entries for Haas and Crooks (1999) and Case and Fisher (1998) below. A comprehensive GIS database of their results was made available for research and monitoring.

Conservation and restoration of numerous lands, and proper management of these lands, is essential to stave off further species losses and ecological collapse in the Puente and Chino Hills.

Puente-Chino “Missing Middle” Analysis
Table 1. Continued. Conservation Biology Institute 9 July 2005 Reference Target Species Major Focus Study Area Methods Relevant Results Recommendations Haas et al. 2002, Case and Fisher 1998 Reptiles and amphibians
Determine distribution and diversity of herpetofauna; identify management needs to maintain diversity.

Scattered locales across the PuenteChino Hills Wildlife Corridor, from Chino Hills State Park to Whittier Hills.

Field methods:Pitfall drift-fence arrays and snake traps. Statistical analyses: Several measures of species richness and diversity analyzed relative to landscape position.

Species richness and diversity were generally highest in the Chino Hills (22 species) and Whittier Hills (14 species), with lower levels in the narrower, more fragmented areas between (10-12 species). The number of sensitive species declined from seven in the Chino Hills to four in the Whittier Hills, and the western limit for some species lies somewhere between Chino Hills and Whittier Hills. Several species (e.g., coast horned lizard, western skink, red diamond rattlesnake) showed decreased population densities moving west through the corridor.

Maintain habitat linkages to maintain gene flow and reestablishment of populations if localized extinctions occur.

PCR 2002 General
wildlife, with focus on large mammals.

Assess onsite biological resources and wildlife movement corridors to understand constraints to development on the ShellAera property.

Shell-Aera property and immediate vicinity; representing the western half of the Missing Middle (between SR-57 and Harbor Blvd.).

Sign reconnaissance; unbaited track stations, camera stations, and scat surveys focused on expected corridors and bottlenecks, such as road crossings; analysis of roadkill records.

Documented use of Shell-Aera property by deer, bobcat, coyote, roadrunners, and other native wildlife. Greatest evidence of wildlife movement was concentrated from the southeast corner of the property (associated with Tonner Bridge) to the northwest corner (associated with Drainage 26 and an area of high roadkill on Harbor Blvd.). Documented primary and secondary movement corridors across the property.

N/A--This biological constraints analysis describes existing conditions on the property and does not present recommendations.

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Methods
This study synthesized and updated existing information on wildlife distribution and movements in the Puente-Chino Hills Wildlife Corridor (see Table 1) to serve as a “meta-analysis” of overall corridor function and of the role that each portion of the corridor plays in supporting native wildlife and wildlife movement. After analyzing existing conditions, I also considered how land-use changes in the Missing Middle could affect the continued persistence of wildlife populations throughout the corridor and in each portion of the corridor. The analytical process involved

1. Selecting a suite of target species for which there is sufficient local information to assess distribution and movements;

2. Defining geographic units of the corridor system and assessing their functions in supporting these target species;

3. Assessing the roads that segment the study area as potential barriers or filters to movement; and

4. Assessing how the current functionality of these segments could change with various development scenarios.

Reconnaissance
The analysis of existing literature was supplemented with reconnaissance surveys in the field as well as using satellite imagery, high-resolution aerial photographs, and digital photographs taken during flyovers by Melanie Schlotterbeck. In particular I used the Keyhole program (www.keyhole.com) to perform a “virtual reconnaissance” of the study area, including properties where physical access was not possible. Keyhole3
allows a user to zoom, pan, tilt, rotate, and
otherwise explore a three-dimensional digital model of the Earth’s surface covered with high resolution satellite imagery (2004-5 color images at 1-m resolution) and Geographic Information System (GIS) data that can be layered onto this imagery. This proved to be an ideal tool for “exploring” the terrain prior to the field visit, and while reviewing previous studies in the area, to determine how topography, vegetation, development, and other landscape features might influence target species movements. By zooming in, rotating, tilting, and moving along this virtual landscape, a wildlife biologist can readily see where steep terrain, road cuts, bridges, vegetation, housing developments, and other landscape features would tend to funnel movements by larger species across the study area. (For example, I predicted, based on Keyhole reconnaissance, that the stretch of Harbor Boulevard just south of Wellington Lane would be a deadly road crossing for large mammals, which was later confirmed by personal observations in the field and my literature review.)

3 Reduced-resolution screen captures of Keyhole imagery are used to illustrate landscape issues throughout this report.

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After extensive exploration of the study area using Keyhole, GIS, and high-resolution aerial imagery, I visited the study area on March 2, 2005. I drove all roads crossing the area, stopping to investigate road-crossing structures (bridges, culverts, etc.), walking sections of trails, and looking for wildlife and wildlife sign. I photographed key locations, roadkills, habitat conditions, and other pertinent scenes, and noted signs of wildlife on aerial photographs.

Because my fairly cursory field observations strongly reinforced the quantitative results of more intensive studies (see Table 1), they are not presented in detail, but are cited as supporting or supplemental evidence for the results and recommendations of these previous studies.

Target Species
It is important to clearly define what species and ecological processes are expected to benefit from a wildlife movement corridor (Rosenberg et al. 1997, Beier et al. in press). Target species were selected based on data availability (see Table 1) and how well they reflect overall corridor function or serve as indicators of habitat fragmentation and movement constraints. They include species that require large areas to survive, are most susceptible to extirpation by habitat fragmentation, are most susceptible to roadkill, or for which roads may serve as physical barriers. In addition, previous studies provide some more general measures of ecosystem health and corridor function, such as species richness for amphibians and reptiles (Haas et al. 2002) and avifauna (Cooper 2000).

Although it is tempting to think of one or a few larger mammal species as most obviously served by movement corridors, the ecological effects are far broader than any single species or set of species. Ultimately, the objective of securing and managing the Puente-Chino Hills Wildlife Corridor is more than ensuring that mountain lions can continue roaming the area (although that is certainly one objective)—it is ensuring that healthy ecological communities can continue to thrive and support the broadest possible range of native species.

Mountain Lion
The mountain lion or puma (Puma concolor) is the top carnivore in Southern California. It is a true “keystone” species whose presence helps maintain ecological balance by controlling populations of deer and other prey (Soulé and Terborgh 1999, Crooks and Soulé 1999).

Mountain lions require huge contiguous habitat blocks to persist, with individual lions roaming home ranges as large or larger than the entire Puente-Chino Hills study area. Only contiguous habitat areas large enough to support at least 20 individuals—about 2,000 sq. km in Southern California—are expected to support lion populations over even the short term (Beier 1993, Beier et al. in press). Due to demographic instability and inbreeding concerns, even populations meeting these criteria, such as the population of about 20 adult lions occupying the 2,070-sq.-km Santa Ana Mountains Range, must be connected to even larger populations for long-term persistence (Beier 1993).

Although the Puente-Chino Hills are too small (at about 163 sq. km) to support a population of mountain lions on their own, one to several lions live totally or partially within the hills as an Puente-Chino “Missing Middle” Analysis
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extension of the larger Santa Ana Mountains population (Beier 1993, Noss et al. 1997). The Coal Canyon wildlife underpass on Highway 91 was restored specifically to ensure the continued presence of these large predators in the Puente and Chino Hills, thus ensuring a more healthy and balanced ecosystem (Noss et al. 1997). Lions have been detected all the way to the westernmost portions of the corridor (Whittier Hills) in recent years (A. Henderson, A. Gullo, and C.

Schlotterbeck, personal communications).

Lions are very prone to roadkill. During Beier’s (1993, 1995) study of mountain lions in the Santa Ana Mountains, vehicles killed 33% of the population, including four lions killed at one road-crossing during a 2-year period. Thus, mountain lions are good focal species for conservation planning in the study area, due to their keystone status, large area requirements, dependence on intact corridors, and susceptibility to roadkill.

Bobcat
Bobcats (Lynx rufus) are excellent indicators of functional landscape connections at the scale of interest in the Puente-Chino Hills study area (Crooks 2002, Haas 2002, Tigas et al. 2002, Riley et al. 2003). In Southern California, bobcat home ranges average about 2 to 6 sq. km, and population densities average about 1.1 to 1.6 bobcats per sq. km (Riley et al. 2003, Lembeck 1978, Lyren 2001). The probability of bobcat occurrence in a habitat patch is directly related to both the size of the patch and its isolation from other patches (Crooks 2002), with patches as small as 10 sq. km highly likely to support a few individuals if they are close enough together (within 1 km or less) and adequately connected to allow inter-patch movement (Crooks 2002).

Using radio telemetry in the Santa Monica Mountains, Riley et al. (2003) found habitat blocks as small as 3.15 sq. km to support a few individuals, as long as movement was possible to larger, source population areas. Taking into account variation in habitat quality, Beier et al. (in press) concluded that contiguous habitat blocks of about 60 sq. km are necessary to support potential source populations of 20-25 adult bobcats over the short term in Southern California. Noss et al. (1997) estimated that a population of less than 50 bobcats inhabited the Puente and Chino Hills and less than 500 bobcats inhabited the Santa Ana Mountains. Haas (2002) found bobcats to be associated with wider portions of the Puente-Chino Hills, with lower densities in narrower segments. He concluded that bobcats used smaller segments primarily as “move-through” rather than “live-in” habitat.

Bobcats are behaviorally secretive and tend to avoid roads and other human disturbances, although they remain quite susceptible to roadkill. Bobcats are less likely to use road underpasses than coyotes, especially narrow underpasses or underpasses near residential areas, and so may be better indicators of high-quality road-crossing structures for wildlife.

Coyote
Coyotes (Canis latrans) are more adaptable, more abundant, and less averse to fragmentation than bobcats and mountain lions—and thus less dependent on high-quality landscape connections. Nevertheless, coyotes are important to maintaining ecological balance (Crooks and Puente-Chino “Missing Middle” Analysis
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Soulé 1999) and are good indicators of problem road-crossings, as many are killed on roads in the study area and elsewhere (Lyren 2001, Haas 2000, Robertson et al. 1995). Concentrations of coyote roadkills provide good indicators of potential crossing locations for other species, including bobcats, mountain lions, and mule deer. Noss et al. (1997) estimated a carrying capacity of roughly 60 adult coyotes for the Puente and Chino Hills and less than 500 in the Santa Ana Mountains.

Mule Deer
Mule deer (Odocoileus hemionus) are the primary prey of mountain lions and require relatively large habitat areas to support populations. Although they adapt to living in close proximity to humans, and are found in portions of the study area that are effected by fragmentation and development edges (Haas 2000), they are prone to roadkill and highly selective of road-crossing structures. In general, deer will use only the largest, most open types of structures (bridges or very open box culverts) within well-vegetated habitat areas to cross under (or over) roads (Haas 2000, Clevenger and Waltho 1999, Evink 2002). Noss et al. (1997) estimated that about 400 mule deer may inhabit the Puente and Chino Hills and about 4,000 may inhabit the Santa Ana Mountains.

Greater Roadrunner
Greater roadrunners (Geococcyx californianus) are associated with coastal scrub and open brush mosaics in coastal Southern California. They are highly susceptible to roadkill (Unitt 2004) and particularly sensitive to habitat fragmentation, rapidly disappearing from isolated habitat patches (Unitt 2004, Crooks et al. 2001, Soulé et al. 1988, Garrett and Dunn 1981). Soulé et al. (1988) and Crooks et al. (2001) identified the roadrunner as the most sensitive to habitat fragmentation of eight scrub-dwelling species they addressed in San Diego County. Crooks et al. (2001) found roadrunners persisting in only one of 34 canyons isolated by urbanization, and estimated that the roadrunner has a good chance of persisting only in patches 1.6 sq. km or larger. Based on more exhaustive surveys, Unitt (2004) concluded that this underestimates roadrunner sensitivity to isolation; he suggested that even 4.0-sq. km patches may be too small to sustain populations for long. As snakes and lizards are important prey, roadrunners may decline with reductions in reptile diversity and abundance.

Cooper (2000) reported that roadrunners are scattered in association with scrub habitats throughout the Puente-Chino Hills study area, with particular concentrations in the hills north of Brea and Yorba Linda (including significant portions of the Missing Middle). He estimated there were more than 50 breeding pairs (100 adult individuals) living in the Puente and Chino Hills.

Coast Horned Lizard
The coast horned lizard (Phrynosoma coronatum) was once common and widely distributed in coastal sage and chaparral habitats of Southern California, but has been extirpated from much of Puente-Chino “Missing Middle” Analysis
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its former range by habitat loss and fragmentation (Fisher et al. 2002). This species is highly impacted by edge effects, such as invasions by the nonnative Argentine ant, which eliminates the native harvester ants that comprise more than 95% of the horned lizard’s diet (Suarez et al. 2000). Argentine ants are closely associated with human-altered (especially irrigated) landscapes in Southern California, but can invade hundreds of meters into native scrub habitats; their adverse effects on native invertebrate populations ripple through the ecological community with devastating effects on biological diversity (Suarez et al. 1998). Thus, horned lizards serve as good indicators of relatively intact ecological webs and processes or, conversely, of the adverse effects of habitat fragmentation and edge effects on ecological communities (Fisher et al. 2002). They are also highly susceptible to roadkill and trampling. Case and Fisher (1998) and Haas et al. (2002) found coast horned lizards in the Chino Hills, as far west as the ridges between Carbon Canyon and Tonner Canyon (near the Olinda Landfill), but did not detect them at points farther west. Therefore, this species may already be extirpated, or likely will be soon, in corridor segments west of Highway 57 due to isolation of populations by roads and high mortality in remaining habitat areas.

Other Target Resources
The above target species certainly do not comprise a complete list of resources subject to loss due to habitat fragmentation and associated effects. They serve as indicators for a much more diverse community of organisms, and were chosen largely on this basis as well as the availability of distribution data in the study area. In addition to these species, I examined information on the diversity and abundance of reptiles and amphibians (from Case and Fisher 1998, Haas et al. 2002) and birds (Cooper 2000), and considered, at least qualitatively, the effects of habitat fragmentation on other species and ecological processes in the study area.

Defining Geographic Units, Barriers, and Filters
Although the entire study area serves as a wildlife movement corridor at a gross scale, it functions more like a peninsula of somewhat discrete habitat blocks segmented by roads and other discontinuities (Haas 2000, Haas and Crooks 1999, Schlotterbeck 2001, Robertson et al. 1995). The Puente-Chino Hills Wildlife Corridor was therefore subdivided into discrete geographic units based on habitat contiguity and intervening roads. Each unit, including the Santa Ana Mountains (the core area from which the corridor system projects) and the isolated terminal segment at the Whittier Narrows (Robertson et al. 1995), was given a geographic name to facilitate comparison (Map 2). Following Haas and Crooks (1999), the seven units between these two extremes (or between Highway 91 and Interstate 605) were also numbered 1 to 7, from east to west. These seven segments comprise the functional Puente-Chino Hills Wildlife Corridor system. They are convenient for comparing results across the various field studies and for assessing how each segment, and the habitat breaks between them, contribute to overall functionality of the corridor system. These segments are therefore useful tools for conservation planning.

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Map 2. Geographic units of the Puente-Chino Hills Wildlife Corridor.

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Initial Classification of Geographic Units
Each geographic unit was first classified by the primary role it appears to play in the overall functioning of the wildlife corridor system—as a biological core, subcore, patch, or isolate.

These functional categories, defined below, reflect the relative size and contiguity of the units and their ability to sustain populations or facilitate movements of target species, as supported by literature and results of previous wildlife studies here. These definitions are tailored to this particular study, based on well established conventions in reserve design (e.g., Noss 1987, Meffe and Carroll 1997, Soulé and Terborgh 1999), and modified slightly from concepts and definitions developed for the South Coast Missing Linkages project—a science-driven approach to conserving landscape connectivity throughout the South Coast ecosystem (Beier et al. in press). The most significant deviation from the definitions of Beier et al. (in press) is the inclusion of an intermediate-sized “subcore” class (which corresponds to a “patch” in Beier et al. in press).4

• Core — A core area must be large enough (> 2,000 sq. km) to sustain populations of most or all target species without the need for frequent immigration from other areas, and should have relatively high biological diversity and a low proportion of edge. Core areas support source populations of target species, which may contribute individuals to other, less substantial, blocks of habitat. Basically, a core should be large enough to support a population (at least over the short term) of the most wide-ranging and area-dependent target species, which in this case is the mountain lion. • Subcore — Subcores are contiguous blocks of habitat at least 60 sq. km, but less than 2,000 sq. km (corresponding to a “patch” as defined by Beier et al. in press). Subcores are too small to sustain a population of mountain lions in isolation, but large enough to support a population of bobcats with at least occasional dispersal. Subcores may support one or a few individual mountain lions, or at least provide significant “live-in” habitat as part of one or more lion home ranges. Subcores are more edge-effected than cores and may sustain lower overall species diversity, but can nevertheless represent significant source populations for numerous other target species, such as roadrunners, coyotes, and horned lizards.
• Patch — Patches, at less than 60 sq. km, are smaller and more edge-effected than subcores and are expected to support overall lower numbers and diversity of species. In isolation, patches may be too small to support a population of bobcats, and perhaps other target species having intermediate area requirements, although they could support a small number of such species or at least represent live-in or move-through habitat for individuals of such species. Although they may support populations of less area-

4 Concepts like “core” and “corridor” are species- and scale-dependent, such that what might be considered a movement corridor for one species (e.g., mountain lion) can be core “live-in” habitat for other species (e.g., lizards, songbirds, or rodents). This entire study area is widely recognized as a “wildlife corridor,” even though numerous on-the-ground travel routes, population concentrations, etc., can exist within this overall corridor system at finer resolution.

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dependent target species, patches may serve mainly as dispersal stepping stones (or “move-through” habitat) for individuals of larger species (like mountain lions) moving between larger geographic units.
• Isolate — An isolate is any patch that is separated from another geographic unit by barriers to movement for target species. For example, the Whittier Narrows are separated from the Whittier Hills by Interstate 605, other significant roads, and commercial development, and are considered functionally isolated from the corridor for nearly all reptiles, amphibians, and mammals (Haas and Crooks 1999, Haas et al. 2000, Robertson et al. 1995, personal observations).

Note that these initial landscape categories were defined based primarily on the needs of the most area-dependent target species (mountain lion and bobcat). However, such concepts as “core” and “patch” can also be defined separately for each target species, based on their own requirements. Thus, a patch of habitat too small to support mountain lions could represent a “core” population area for less area-dependent species, like the roadrunner or horned lizard.

Such species-specific issues were treated in more detail in later analytical steps.

Classifying Barriers and Filters to Movement
Roads and other discontinuities in habitat were also classified based on their relative effects on movements and population distributions of species, as follows:
• Barriers and Near Barriers — Roads or other discontinuities between geographic units that are never (for barriers) or rarely (for near barriers) crossed by target species. Barriers effectively isolate target species populations on adjacent habitat units from one another, while near barriers may separate subpopulations into a “metapopulation” system, with individuals occasionally dispersing between subpopulations in different units. For wideranging species like bobcats or mountain lions, barriers or near barriers may define one boundary of a home range, as individuals recognize it as the edge of available habitat.

Major freeways and associated physical features (e.g., embankments, drainage improvements, retaining walls, lane dividers, fences, wide areas devoid of vegetation) create impassible barriers for nearly all ground-dwelling species, unless sufficient crossing structures (e.g., bridges, culverts, vegetated over-crossings) facilitate movements (Beier et al. in press, Evink 2002, Haas 2002, Lyren 2001). For example, the concentration of roads and commercial developments associated with Interstate 605, separating Whittier Hills from Whittier Narrows, represents a barrier for most or all target species. Near barriers are similar, but they may have one or more crossing structures that can be used by at least some target species; or target species may occasionally cross atgrade, on the road surface (perhaps at high risk of roadkill). Highway 57 and Harbor Boulevard are examples of near barriers in the study area. Both have high traffic volumes and physical characteristics that discourage crossings, except at one excellent bridge crossing at Tonner Canyon (for Highway 57) and one stretch where wildlife cross Harbor Boulevard at-grade—albeit with frequent roadkill.

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• Filter (Permeable and Highly Permeable) — Filters are discontinuities in habitat connectivity that are readily to moderately crossable by most but not all target species.

For example, two-lane paved roads with low traffic volumes and little associated development are readily crossed by larger mammals (although there may be occasional roadkill); but other species, like horned lizards, may be reluctant to cross or may suffer high roadkill. Thus, such roads serve to “filter” some species out of the community of wildlife crossing between adjoining habitat units. Several permeable to highly permeable roads cross the study area, such as Turnbull Canyon Road through the Whittier Hills (between Segments 6 and 7). The larger mammals, roadrunners, and some reptiles probably cross this road at-grade with little hesitation, and individual home ranges may straddle it. However, some smaller or more sedentary species may have their populations segmented by this road into subpopulations, with only occasional cross-road dispersal.

Analyses — Assessing Existing and Future Functionality
For each target species, I followed the following analytical steps:

1. I assigned each of the nine geographic segments to one of the functional categories (core, subcore, patch) as if each functioned independently of the others (i.e., as if roads separating the units acted as barriers or near barriers to dispersal). This initial categorization was based exclusively on unit size. For example, any unit less than 60 sq. km would be considered a patch if it functioned independently of other units in supporting a target species.

2. I assessed each road separating the units to determine whether it acted as a barrier (or near barrier) or filter (permeable to highly permeable). If a road was not considered a barrier/near barrier for a target species, and the two units it separated appeared to function as one larger unit for that species, the area of the two units was summed and the function of the new composite unit was reassessed. For example, if the composite unit exceeded 60 sq. km, it was considered to function as a subcore rather than two separate patches.

3. Based on this revised, species-specific functionality assessment, I assigned each newly defined unit (or composite unit) a function relative to supporting individuals or populations of each target species based on unit size, habitat composition, and other factors gleaned from the literature and field reconnaissance. These species-specific functions were defined as follows:
• Population — capable of supporting a breeding population of at least 20 adults and potentially serving as a source of individuals that disperse into other units. • Subpopulation — capable of supporting at least two but less than 20 breeding individuals. Not likely to be a reliable source population, but may exchange individuals with other areas within a larger metapopulation (a set of partially isolated Puente-Chino “Missing Middle” Analysis
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populations linked by occasional dispersal) and may provide individuals to recolonize habitat patches in case of local extirpation.
• Home Range Part — incapable of supporting at least two breeding individuals on its own, but may provide live-in habitat (e.g., foraging or resting cover) and form a part of one or more individuals’ home range(s).
• Move-through — not contributing significant live-in habitat for a species as part of a functional home range, but capable of accommodating movements between more substantial units within a home range, or potentially used for dispersal between other habitat units.

4. This classification system was used to assess likely effects of future scenarios on wildlife populations or movements, such as (a) adding new roads or development that would introduce new barriers or reduce the size of a functional unit, or (b) adding or improving wildlife crossing structures that would allow two independent units to serve as one larger one.

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Results
Functionality of Geographic Units
Table 2 summarizes characteristics of the geographic units, including their size, vegetation composition, known or inferred presence/absence of target species, initial functional classification (core, subcore, patch), and reserve status (conserved/unconserved). Only the Santa Ana Mountains unit met the definition of a core area (larger than 2,000 sq. km and capable of supporting a mountain lion population). The Chino Hills between Highways 91 and 142 met the definition of a subcore (60-2,000 sq. km and capable of supporting a population of bobcats). Six other segments of the Puente-Chino Hills Wildlife Corridor met the definition of patch, but with great variation in their capacity to support wildlife and wildlife movements. The disjunct Whittier Narrows met the definition of an isolate.

Table 3 summarizes pertinent characteristics of the major roads dividing these units, with a focus on their role as barriers or filters to wildlife movement. Following below is a more detailed, unit-by-unit review of the information, concerning how each unit appears to function in supporting wildlife populations and movements, considering the effects of intervening roads and other factors. This review starts with the Santa Ana Mountains Core Area, then describes the seven segments of the functional Puente-Chino Hills Wildlife Corridor, and ends with the isolated Whittier Narrows.

Santa Ana Mountains (Core)
At about 2,070 sq. km, wildlands in the Santa Ana Mountains comprise the only true core in the study area. They support a high diversity of wildlife in a relatively intact and healthy representation of Southern California’s South Coast ecosystem (Spencer et al. 2001), including substantial populations of all the target species. Noss et al. (1997) estimated populations of breeding adults in the Santa Ana Mountains at about 4,000 mule deer, 15-20 mountain lions, up to 500 bobcats, and more than 500 coyotes. These populations are large enough to persist, at least in the short term, within the Santa Anas without immigration from other habitat areas— although at least the mountain lion needs occasional immigration from adjacent mountain ranges to persist in the long term (Noss et al. 1997, Beier 1993). Of course, all species and ecosystem functions benefit from connectivity to other wildlands. The breeding population of about 15-20 mountain lions serves as a source of lions moving into the Puente-Chino Hills via the Coal Canyon Underpass (Beier 1995, Noss et al. 1997).

The Santa Ana core area is separated from the Chino Hills by busy Highway 91 and associated developments. However, the Coal Canyon Wildlife Underpass was restored specifically to mitigate this strong barrier to movements and appears to be functional (Figure 2).

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Segments of the Functional Puente-Chino Hills Wildlife Corridor Santa Ana
Mountains Chino
CarbonTonner Shell-Aera Powder- Schabarum San Miguel E. Whittier W. Whittier Whittier Narrows Segment Number N/A 1 2 3 4 5 6 7 N/A Size (sq. km.) ~2,070 85.6 44.3 13.3 5.7 1.5 5.2 7.1 ~4.5 Vegetation Mosaic Shrubland 51.3% 51.9% 45.2% 48.9% 57.1% 43.4% 67.0% Grassland 36.5% 29.4% 37.7% 21.0% 31.8% 36.1% 17.1% Woodland 12.1% 18.7% 17.2% 30.1% 11.4% 20.4% 15.9% Wetland N/A

0.1% 0.1% 0.0% 0.0% 0.0% 0.0% 0.0%
N/A
Spp. Presence/Absence* Mountain lion P P P P? P? P? P P A? Bobcat P P P P P P P P A? Coyote P P P P P P P P P? Mule deer P P P P P P P P ? Roadrunner P P P P P? P? P P ? Coast horned lizard P P P A? A? A? A? A? A? Biological Function core subcore large patch patch patch small patch patch patch isolate Reserve Status substantially conserved
substantially
conserved
Carbon Cyn
partly
conserved,
Tonner Cyn
unprotected &
threatened
unprotected
& threatened
partly
conserved,
partly
threatened
partly
conserved,
partly
threatened
substantially
conserved
substantially
conserved
substantially
conserved
*See Table 1 for supporting literature. P = confirmed present; A = likely absent; ? = presence or absence inferred by indirect evidence and geographic context, but no confirmatory data found.

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Major, 6-lane freeway with heavy traffic and significant physical barriers to wildlife.

Barrier, except for Coal Canyon Underpass
Carbon Canyon Rd. (SR 142)
Chino/Carbon-Tonner Square box culvert near
Chino State Park entrance.

Busy 2-lane highway through mostly wild open space. Moderate-high coyote roadkill. Few physical barriers.

Permeable filter, with some roadkill (esp. coyote). Mix of at-grade crossings and culverts, at least one used by bobcat.

SR 57 Carbon-Tonner/ShellAera Tonner Canyon Bridge Major 6-lane freeway with heavy traffic and significant physical barriers to wildlife. Barrier except for Tonner Canyon Bridge, with documented use by deer, bobcat, and coyote.

Harbor Blvd. Shell-Aera/PowderSchabarum Harbor Blvd. Wildlife Tunnel (proposed) Major 4-lane arterial with heavy traffic and significant barriers to wildlife. High roadkill. Barrier, except for occasional at-grade crossing, with very high roadkill. Hacienda Blvd. Powder-Schabarum/San Miguel
none (except a littleused equestrian tunnel that could be improved) Busy 2-lane road with steep slopes and cut banks, but several at-grade crossing areas.

Filter, with moderate roadkill risk.

Colima Rd. San Miguel/East Whittier Colima Service Tunnel Busy 4-lane road with physical barriers, including fences that may help funnel wildlife to undercrossing.

Filter, with relatively low roadkill due to fences and a well-used undercrossing with known use by deer, bobcat, and coyote.

Turnbull Canyon Rd.

East Whittier/West Whittier
none Winding, 2-lane road with light traffic
through wild habitat.

Highly permeable filter, with at-grade crossings in wild open space.

Interstate 15 & Workman Rd.

West Whittier/Whittier Narrows
none Major 6-lane freeway with heavy traffic, plus
other major and minor roads, commercial development, and other physical barriers to wildlife.

Barrier to essentially all ground-dwelling species.
*Includes only those structures used by diverse target species and especially larger mammals. Numerous smaller culverts that may serve some target species also occur, as do some larger equestrian tunnels that are in landscape positions not favoring use by target species. See Haas (2000) and Robertson et al. (1995) for a more comprehensive review of crossing structures in the study area.

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Figure 2. View northwest across Coal Canyon Wildlife Underpass, which links wildlife movement between the Santa Ana Mountains and Chino Hills State Park (Keyhole screenshot).

Corridor Segment 1—Chino
At over 85 sq. km, the Chino Hills represent a substantial subcore supporting diverse and relatively healthy ecological communities. It supports one to a few mountain lions, forming at least a portion of their home ranges, due to its connection to the Santa Ana Mountains population via the Coal Canyon Wildlife Underpass. Segment 1 also supports significant populations of all other target species (Lyren 2001, Cooper 2000, Haas and Crooks 1999, Haas 2000, Noss et al. 1997) and has higher overall biological diversity than other segments. For example, of all the segments they sampled for reptiles and amphibians in the Puente-Chino Hills Wildlife Corridor, Haas et al. (2002) reported the highest richness of herpetofauna (22 species captured) in the Chino Hills. They further reported the highest levels of species diversity (using a variety of diversity indices) and evenness (an index of relative abundance across all species) in the Chino Hills, with a general decline in these measures as one moves west through the corridor.

Moreover, the number of sensitive amphibian and reptile species recorded by the study dropped from 7 in the Chino Hills to 4 in the Whittier Hills. No western spadefoot toads (Spea hammondii), western pond turtles (Clemmys marmorata), coast horned lizards, or coast patchnosed snakes (Salvadora hexalepis) were found west of the Chino Hills. These results Puente-Chino “Missing Middle” Analysis
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undoubtedly reflect the larger size of Segment 1 (and adjoining Segment 2) compared with other segments, its proximity to the Santa Ana Mountains Core, and the increasing number of barriers and filters encountered moving west from this source area through the corridor. Similar patterns in diversity, abundance, and evenness measures would be expected for other taxa (e.g., birds, small mammals, insects, plants) if comparable data were available to document them.

Segment 1 is largely conserved already as Chino Hills State Park, although efforts continue to increase the size and buffering of this important reserve area. It is separated from Segment 2 by Carbon Canyon Road (Highway 142). This busy 2-lane road suffers some roadkill, especially coyote (Robertson et al. 1995), but is generally quite permeable to target species due to extensive, naturally vegetated land on both sides, lack of development over much of its length, and availability of several undercrossings. The most significant undercrossing is a 1.4-m (4.5-ft) high square box culvert used by bobcats and other target species (Robertson et al. 1995). This road is therefore classed as a permeable filter, allowing Segments 1 and 2 to function as one larger subcore for most species and ecological processes. Notably, Haas et al. (2002) and Case and Fisher (1998) recorded coast horned lizards on both sides of Carbon Canyon Road, but not farther west along the corridor.5
Corridor Segment 2—Carbon-Tonner
This large (44.3 sq. km) patch appears to function more as an extension of the Chino Hills subcore, being separated only by permeable Carbon Canyon Road (see previous). It is biologically diverse and supports all target species, including the westernmost observations of horned lizards by Haas et al. (2002) and Case and Fisher (1998). The southern portion of Segment 2 (including lower Carbon and Tonner Canyons and associated ridges) has been identified as a conservation priority for birds due to its support of several regionally rare or declining species, including greater roadrunners, loggerhead shrike, cactus wren, California gnatcatcher, grasshopper sparrow, and sage sparrow, among others (Cooper 2000). The northern portion of the segment (upper Tonner Canyon) is also rated as a conservation priority for birds, including golden eagle, burrowing owl, northern harrier, cactus wren, tricolored blackbird, and grasshopper sparrow, among others (Cooper 2000). Tonner Canyon also supports significant California walnut woodlands.

The eastern half of Segment 2 contains the western slopes and ridges of the Carbon Canyon landscape and is partially conserved as part of Chino Hills State Park and the Firestone Scout Reservation. The western half of this segment, containing most of Tonner Canyon, is unconserved and threatened by several proposed developments. Tonner Canyon is almost entirely owned by the City of Industry, which proposes a new road along the east side of Tonner Canyon (Map 2) and new water reservoirs within the canyon. This threatened half of the segment comprises the eastern portion of the Missing Middle.

5 During my literature review, I found no recent confirmed records for coast horned lizards farther west than a ridge between Carbon and Tonner Canyons near Olinda Landfill (Haas et al. 2002). However, one table in a draft report (LSA 2005) listed the species as “observed” in the Whittier Hills, although another table in the same reference indicated the horned lizard as potentially present but not observed there.

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Figure 3. View northeast across Tonner Bridge and Highway 57 (Keyhole screenshot).

Wildlife on both sides of Highway 57 (a barrier road) are funneled to cross under Tonner Bridge.

The Olinda Landfill occupies a large footprint in the south-central part of Segment 2, between Tonner and Carbon Canyons. The landfill eventually will be closed and restored to natural vegetation as a County regional park, adding to the area of conserved open space here (C.

Schlotterbeck, personal communication).

Segment 2 is divided from Segment 3 by busy Highway 57. This freeway is a near total barrier to ground-dwelling wildlife, except for one high-quality underpass in lower Tonner Canyon (Figure 3 and Photo 1). This bridge over Tonner Creek is very wide and open, with sufficient natural cover to facilitate movement by all target species. The bridge is used by mule deer, bobcat, coyote, and numerous other species (PCR 2002, Haas 2000, Haas and Crooks 1999, Robertson et al. 1999, personal observations). Maintaining this function is widely considered critical to maintaining the functional Puente-Chino Hills Wildlife Corridor, but it is threatened by the City of Industry plan for a new road originating here and traveling up Tonner Canyon to Diamond Bar.

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Corridor Segment 3—Shell-Aera
This segment, between Highway 57 and Harbor Boulevard, comprises the western portion of the Missing Middle. It is named for the Shell-Aera Master Planned Community property (2,935 acres or 11.9 sq. km), which comprises 90% of the segment’s remaining undeveloped land and is proposed for development. In addition to the Shell-Aera property, Segment 3 includes some privately owned open space lands conserved as mitigation for previous developments in the vicinity, such as the Shea homes development off of Harbor Boulevard in the northwest portion of the segment.

Although smaller than Segments 1 and 2, and bounded by two near-barrier roads, this substantial habitat block (13.3 sq. km) supports diverse vegetation and wildlife communities and is generally recognized as essential to maintaining connectivity through the Puente-Chino Hills Wildlife Corridor (PCR 2002, PCR 2000, Haas 2000, Robertson et al. 1995, personal observations). Cooper (2000) recognized the area as being of high conservation concern for its support of rare or declining bird species, including greater roadrunner, golden eagle, and grasshopper sparrow, among others. The Shell-Aera property was not open to sampling by most studies included in this analysis. However, PCR (2002) performed biological surveys on the property and confirmed presence and movements of all target species except mountain lion and horned lizard. Although horned lizards are likely extirpated here, mountain lions undoubtedly do use the property—probably both as move-through habitat and as foraging habitat. There is essentially no other way for lions to make it to segments farther west, where lion presence has Photo 1. View east under the Tonner Bridge, the only functional crossing beneath Highway 57 for deer, mountain lion, bobcat, and other wildlife species.

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Figure 4. View northwest across Segment 3 and Harbor Boulevard to Segment 4, indicating general trends in wildlife movements (Keyhole screenshot). Arrow widths indicate inferred relative use levels.

Red dots indicate stretch of highest roadkill.
been confirmed (A. Henderson, A. Gullo, and C. Schlotterbeck, personal communications), from the source populations to the east. The segment also supports deer and other prey species and appears to have suitable cover, despite a history of grazing that has degraded woodland and shrubland habitats. The Shell-Aera property also supports some of the best remaining examples of California walnut woodland in Southern California (approximately 16,000 walnut trees covering 475 acres), although regeneration has been hampered by grazing (Quinn 1998, in PCR 2002).

Harbor Boulevard, which forms the western boundary of Segment 3, is a formidable barrier to target species movement. It is wide, with fast and heavy traffic, and currently lacks any underpasses. A combination of natural and man-altered topography tends to funnel wildlife to a stretch of road just south of the Shea Homes development, where a steep-sided riparian drainage (“Drainage 26”) abuts a steep fill slope below the road, adjacent to housing (Figure 4). A variety of wildlife trails converge here, and several cross the road and continue northwest along a powerline right-of-way into Powder Canyon. Signs of target species usage (bobcat, deer, coyote) are especially abundant in Drainage 26, and roadkill frequency is very high in this stretch of road, especially for coyote (PCR 2002, Robertson et al. 1995, personal observations). Figure 4 illustrates major movement concentrations on the Shell-Aera property as they relate to this problem road-crossing area. Photo 2 shows a road-killed coyote I observed on March 2, 2005, Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute 28 July 2005
where Harbor Boulevard crosses the Shea Homes development after Drainage 26. I surmised that this coyote entered the roadway out of Drainage 26 via one of several clear wildlife trails.

Fortunately, recognition of this problem road-crossing has resulted in approval of a wildlife underpass here, although fencing to direct wildlife to the tunnel, considered essential to its success, has not been approved on the Shell-Aera property (A. Henderson, personal communication).

Corridor Segment 4—Powder-Schabarum
This segment (about 5.7 sq. km) is relatively small but nevertheless significant, especially as a link between larger habitat units to the east and west. Deer, bobcat, and coyote are commonly seen moving through the segment (Robertson et al. 1995). Haas (2000) recorded a lower frequency of bobcat visitations to track stations in this segment (and adjoining Segment 5) than in larger segments in the study area, which he attributed to the narrowness of this stretch of the wildlife corridor and consequently greater edge effects and disturbance factors.

Powder Canyon open space makes up the southern portion of Segment 4, and Schabarum Regional Park makes up the northern portion. The segment averages about 1.5 km wide over most of its length, but narrows to about 0.5 km in the western portion approaching Hacienda Boulevard. Wildlife movement becomes quite constrained in this narrow portion by existing housing, fences, and other impediments. Hacienda Boulevard separates this constrained portion of Segment 4 from Segment 5. Although Hacienda Boulevard has lower traffic volumes and speeds than the highways discussed above, it has very steep slopes and cuts, with no reliably Photo 2. View southeast across the Harbor Boulevard “deathtrap.” Drainage 26 extends out of view to the left from the bend in Harbor Boulevard. Note road-killed coyote and heavy traffic.

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used crossing structures. An existing equestrian tunnel, that is infrequently used by target species, could be improved with fencing and revegetation (Haas 2000 and personal observations). Hacienda Boulevard has several at-grade crossing concentrations and trails (Haas 2000, Robertson et al. 1995, personal observations), which are probably associated with moderate roadkill. I rated this as a permeable filter, as it is crossable by most target species; however, it may act as a strong filter due to these and other constraints, and it represents a bottleneck to movement in need of improvement (Haas 2000).

Corridor Segment 5—San Miguel
This is the smallest (1.5 sq. km) segment of the entire corridor system. Along with the narrow constriction in the west end of Segment 4, this segment represents the narrowest habitat constriction along the wildlife corridor system (0.5 to 1.0 km wide). It is also perhaps the most disturbed by humans and their pets, particularly on northern slopes (Haas 2000, Robertson et al. 1995). Haas recorded low use by target species (no bobcat use) on the northern portions of this segment, along the Skyline Trail, but high levels of cats, dogs, striped skunks, and raccoons. The abundance of these mesopredators that are adapted to human environments often reflects low presence of coyotes and other large predators, which suppress these species when present (Crooks and Soulé 1999), as well as higher human influences and edge effects. Haas (2000) recorded bobcat activity in the southern portion of the segment, in association with less disturbed areas of San Miguel Canyon and near Skyline Drive. He noted that the transects with the greatest bobcat activity were also those with the lowest dog activity. Haas surmised (as did Robertson et al. 1995) that large mammals travel along Skyline Drive and descend into San Miguel Canyon towards the Colima Service Tunnel (discussed below). Low density housing in this segment, especially near Hacienda Boulevard, may reduce habitat quality for target species, but does not present barriers to movement (Haas 2000, Robertson et al. 1995). For some target species, Segment 5 may function primarily as move-through habitat, although a few coyotes and bobcats probably forage in San Miguel Canyon.

Segments 5 and 6 are divided by Colima Road, a fairly busy 4-lane road winding through a mix of open space and scattered housing. Although flanked by steep slopes, some fences, and other movement impediments, there are several at-grade crossing areas, which are associated with high coyote roadkill (Haas 2000, Robertson et al. 1995). One good under-crossing structure exists at a service tunnel near the southern edge of the habitat area (Colima Service Tunnel). Bobcats, coyotes, and deer use this tunnel (Robertson et al. 1995, Haas 2000, Haas and Turschak 2002), and they continued using it even after a dramatic increase in recreational uses of the tunnel and vicinity by humans and dogs during 2001-2002 (Haas and Turschak 2002). Most wildlife species use the tunnel between sunset and sunrise, whereas human and dog use occurs almost exclusively during daylight (Haas and Turschak 2002). Conserving and improving this tunnel for continued wildlife use, especially at night, is a conservation priority.

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Corridor Segments 6 and 7—East Whittier and West Whittier The wildlife corridor widens again in the Whittier Hills from the narrow and constrained Segments 4 and 5. Segments 6 and 7 are separated by Turnbull Canyon Road, which appears to be the most permeable road analyzed in the study area. It is a narrow, 2-lane road with relatively light traffic, winding through fairly undisturbed wildlands. Haas (2000) recorded no roadkills here and did not consider Turnbull Canyon Road a barrier or major hazard to mammals.

Likewise, Robertson et al. (1995) did not consider Turnbull Canyon Road a significant impediment to movement, which corresponds with my field observations. Consequently, Segments 6 and 7 are discussed here together as one continuous geographic unit (Whittier Hills).

The Whittier Hills support significant biological values despite their location at the terminus of the range of connected wildlands, far from the Santa Ana Mountains Core. This area had the highest levels of deer and bobcat activity recorded by Haas (2000), and higher species richness of reptiles and amphibians than narrower segments farther east (Haas et al. 2002). Mountain lion presence has recently been confirmed in the area by several lion-predated goats and deer, and at least one likely lion scat (Haas 2000; A. Henderson, C. Schlotterbeck, and A. Gullo, personal communications).

However, monitoring results also show that the Whittier Hills have lost some species and may be close to losing more due to their distance from core areas and numerous intervening barriers and filters to movement. For example, despite the relatively high total number of reptile and amphibian species they recorded here, Haas et al. (2002) also found the Whittier Hills to have the lowest overall evenness in the study area (Haas et al. 2002). This evenness finding means that the local herpetofauna consists of a few abundant species plus many less abundant species, in contrast to the Chino Hills, where high evenness indicated healthy populations of most species.

Those species detected in low numbers in the Whittier Hills may represent remnants of dwindling populations, possibly on their way to extirpation with little hope of being “rescued” by new colonists from other areas (Brown and Kodric-Brown 1977) due to the great distances and numerous barriers involved. Moreover, the Whittier Hills support fewer sensitive species of reptiles and amphibians than the Chino Hills, as various species drop out in an apparent east-west gradient from the Chino Hills through the wildlife corridor to the Whittier Hills (Case and Fisher 1998, Haas et al. 2002).

The Whittier Hills are separated from the Whittier Narrows by an array of formidable barriers, including Workman Road, Interstate 605, and a wide, unbroken surface of buildings and pavement. Together, these create a near total barrier to movement for all target species.

Whittier Narrows (Isolate)
Because it is functionally isolated from the Puente-Chino Hills Wildlife Corridor, I did not investigate this area in detail. Although this matrix of wetland and disturbed upland habitats probably supports some coyotes (a semi-isolated subpopulation?), it is unlikely to support other target species in perpetuity.

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Summary of Overall Corridor Function
In general, the Puente-Chino Hills Wildlife Corridor appears to be functional for at least larger mammals and birds, although tenuously so in the Missing Middle (due to several barrier roads and near barrier roads) and across smaller Segments 4 and 5 just west of the Missing Middle (due to their small size, strong edge effects, and high human and dog activity). Essentially all roads in the study area are considered barriers or at least strong filters to movements by many reptiles, amphibians, and small mammals, although most birds and larger mammals currently can move between all segments either at-grade (with mortality risks) or via critical crossing structures. Despite constraints in many locations along the corridor, target species are confirmed or highly likely to occur in all seven corridor segments, except for the coast horned lizard, which may already be absent, or will disappear in the future, west of Highway 57.

Mountain lions are capable of traversing the length of the corridor, albeit at some risk of roadkill, and one or more lions still hunt as far west as the Whittier Hills. Most other target species probably persist over the length of the corridor as metapopulations, with subpopulations segregated among geographic units by the presence of barrier or near barrier roads. These subpopulations may be linked demographically and genetically by occasional dispersal, or by within-home range movements of some individuals, depending on each species’ ability to navigate roads and crossing structures. For example, bobcats apparently have small subpopulations living in the Whittier Hills and within Segment 3 (Shell-Aera), and a larger source population living within the Chino Hills (Segments 1 and 2). Some individual bobcats probably have home ranges completely or partially within smaller segments (e.g., 4 and 5) between these more substantial habitat areas; or they occasionally move through the smaller segments, between larger ones, and thus keep the overall metapopulation interconnected demographically and genetically. This metapopulation persistence depends on both occasional cross-road movements (i.e., functional road-crossings) and sufficient patch size and habitat quality to sustain small subpopulations within segments.

Haas et al. (2002) described a gradient of declining diversity and evenness of reptile and amphibian species, moving west from the Chino Hills. This must be attributed to higher mortality and edge effects in the more fragmented portions of the study area, exacerbated by the greater distance and increasing number of barriers and filters that must be crossed as one moves farther west from source populations. This pattern of decreasing biological diversity in the western portions of the corridor is likely to be mirrored by other taxa that respond similarly to distance and barrier effects, such as small mammals. In terms of metapopulation dynamics, if a local population or subpopulation dwindles or disappears from one segment (e.g., Whittier Hills), it is less likely to be “rescued” by colonists from other segments (e.g., Chino Hills) the farther away it is from the source population and the greater the number of intervening barriers and filters. Hence, the farther west a segment lies, the greater the likelihood of local population declines or extirpations, at least for less mobile species (Haas et al. 2002).

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Table 4 summarizes the conclusions from the preceding review of geographic units and roads and presents a conceptual model of how each geographic unit (or composites of adjoining units lacking barriers) appears to function in supporting populations of target species within this segregated landscape. This table integrates diverse information, including published estimates of home ranges and densities of target species in Southern California, results of the monitoring studies summarized in Table 1, variation in habitat quality and mortality factors throughout the study area, and professional judgment. The carrying capacity estimates (in parentheses for some species) are rough approximations only, intended as order-of-magnitude estimates of the capacity of each geographic unit to support populations or subpopulations of target species, or to function as part of one or more home ranges, or to function as pass-through habitat between other units.

Where adjoining segments are considered to function as one unit for a particular target species (e.g., if individuals readily cross roads and populations are not considered segmented by them), the area of those segments is summed. Thus, Segments 1 and 2 are combined to form new Segment 1/2 (Chino-Tonner), because Carbon Canyon Road is quite permeable for most species.

Likewise, Segments 6 and 7 (the Whittier Hills) appear to serve as one contiguous geographic unit for nearly all target species, except the horned lizard, which is likely absent.

Vertical lines separating adjacent segments in Table 4 represent roads considered to segment populations for a given species. However, note that even where barrier roads do not prevent movement between adjoining segments, those segments may be treated separately in the table’s classification of segment function for a target species. For example, although the roads bounding Segment 5 are not considered mountain lion barriers, Segment 5 is rated separately as “passthrough habitat” for lions (due to small size and edge constraints), whereas Segment 4 and combined Segments 6/7 are considered foraging habitat and therefore parts of a functional home range for one or two lions that pass through Segment 5 to reach them. Similarly, although Colima Road is not a strong barrier to movement for bobcats, coyotes, or deer, narrow and edgeeffected Segments 4 and 5 likely support, at most, small subpopulations (a few resident individuals) or portions of a few individual home ranges for these species, whereas the larger and more contiguous Whittier Hills unit can support more robust and sustainable subpopulations.

By reading across the rows of Table 4 for any species, one can envision how the presence of species is maintained throughout the corridor via individual movements and metapopulation dynamics, with each segment (or combination of segments) serving as stepping stones along the way (either for an individual of a wide-ranging species like mountain lion—which may traverse the entire corridor—or over several generations for smaller species, whose individuals may move over only one or a few segments in a lifetime). For example, the only source population for mountain lions is the Santa Ana Mountains Core. The one to three resident lions that use the combined Chino-Tonner unit would not be there without this core population or the Coal Canyon Wildlife Underpass (Beier 1993, Noss et al. 1997, Haas 2000). One or more of these resident lions at least occasionally use Segment 3 (Shell-Aera) as foraging or pass-through habitat as a portion of their home range (made possible by the Tonner Bridge between Segments 2 and 3).

From there, one or more lions occasionally forage in or move through Powder Canyon (Segment 4) and San Miguel Canyon (Segment 5) to forage in the Whittier Hills (combined Segments 6/7).

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Segments of the Functional Puente-Chino Hills Wildlife Corridor 1/2–Chino-Tonner 6/7–Whittier Hills
Santa Ana Mtns
Core Area 1-Chino
2-CarbonTonner 3-Shell-Aera 4-Powder- Schabarum 5-San Miguel 6-E. Whittier 7-W. Whittier Whittier
Narrows
(Isolate)
Unit Size (sq. km) 85.6 44.3 5.7 1.5 5.2 7.1 Summed Size ~2,070
129.9 13.3 7.2 12.3
~4.5
Target Species Mountain lion Pop (15-20) Subpop (1-3) HR Part (1-2) HR Part (1-2) Pass-thru HR Part (1-2) Absent Bobcat Pop (100-400) Pop (20-50) Subpop (2-10) Subpop/HR Part (2-5) Subpop (5-15) Absent? Coyote Pop (200-500) Pop (20-50) Subpop (5-12) Subpop/HR Part (2-7) Subpop (15-25) Subpop? Mule deer Pop (2,000-4,000) Pop (100-300) Subpop (10-25?) Subpop/HR Part (5-15) Subpop (15-30) Absent? Roadrunner Pop (hundreds) Pop (20-100) Subpop (?) Subpop (?) HR Part (?) Pop(?) Absent? Coast horned lizard Pop (thousands) Pop (hundreds?) Pop (hundreds?) Absent? Absent? Absent? Absent? Absent? Absent? Pop = capable of supporting a breeding population of >20 individuals and potentially serving as a source population via dispersal to other segments.

Subpop = capable of supporting 2-19 individuals as part of a metapopulation connected by at least occasional dispersal between other segments. HR Part = could comprise part of one or more individual home ranges in concert with adjoining areas, but by itself is unlikely to support a breeding pair. Pass-thru = used for movement between adjoining units, but unlikely to support individual life requisites (foraging, breeding, etc.) or a home range.

SR 57
Harbor Blvd
Colima Rd
SR 91
I- 605
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If any of the critical road crossings becomes non-functional, lions would no longer use more westerly segments, because no segments are capable of supporting a population of lions in isolation (other than the Santa Ana Mountains Core). Moreover, if any segment is reduced in size or quality to become only move-through habitat (rather than live-in habitat), the probability of lions using this unit, or any units lying further west, would drop considerably. Hence, maintaining lions in the Whittier Hills ecosystem depends not only on maintaining the possibility of unimpeded movement by individuals along the corridor, but also on maintaining substantial live-in habitat along the way.

Similarly, subpopulations in the Whittier Hills of bobcats, mule deer, roadrunners, and, to a lesser extent, coyotes exist in part due to other population or subpopulation segments (i.e., source habitats) along the corridor. Thus, the substantial habitat blocks in Segments 2 and 3 are important to continued presence of target species many kilometers away in the Whittier Hills.

Substantial reduction in the carrying capacity of any one segment increases the probability of species losses in other segments. Thus, for example, the large area of Segment 3 (Shell-Aera) is a major potential contributor to the continued presence of bobcats, mule deer, mountain lions, roadrunners, and many other species in the Whittier Hills, especially if habitat quality is increased and road crossings are improved.

To summarize, the ability of westerly segments of the corridor to support species depends both on (1) the potential for individual movement between each set of adjoining segments (a function of roads and road crossings), and (2) having sufficient live-in habitat along the way to support populations or subpopulations that contribute dispersing individuals. The greater the distance from or between source populations, the lower the probability of a habitat patch or group of patches to continue supporting that species. If the distance between occupied segments becomes too great, or if barriers prevent inter-segment movement, local extinctions are inevitable in the isolated segments. Thus, any reduction in the capacity of segments to support populations or subpopulations increases the probability of local extinctions in that segment, as well as in all other “downstream” segments to the west.

Importance of the Missing Middle to Corridor Function
This understanding of overall corridor function highlights the importance of the Missing Middle as a part of larger home ranges for more area-dependent species and for maintaining species use of segments farther west. Although there has been much attention to maintaining or improving road-crossing structures and avoiding new impediments to movement, there should be equal attention to maintaining functional habitat blocks, capable of supporting source populations of target species, within the Missing Middle. Currently, the eastern half of the Missing Middle (Tonner Canyon) serves as an extension of the large Chino-Tonner subcore, contributing dispersing individuals of target species to other segments. Likewise, Segment 3 (Shell-Aera), although somewhat smaller and degraded by grazing, undoubtedly supports significant numbers of target species that disperse (at some risk) across Harbor Boulevard into Powder Canyon and beyond.

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Future Corridor Functions
The above assessment of population distribution and movements, as summarized in Table 4, can serve as a foundation for assessing likely effects of future projects on the functionality of individual segments or the wildlife corridor as a whole. Although it is beyond the scope of this report to comprehensively analyze any particular project, I qualitatively assessed the likely effects of several proposed projects using the conceptual model presented above. I selected three proposed projects that most threaten corridor function in the Missing Middle and may eliminate wildlife populations and ecosystem functions throughout a much greater area of the Puente and Chino Hills. By impeding species movements or metapopulation dynamics within this peninsula of wild, a project’s impacts may extend far beyond its boundaries, potentially rippling through the range of hills to eliminate wildlife populations as far west as the Whittier Hills.

Shell-Aera Master Planned Community
This planned community of 3,600 homes would be scattered over most of Segment 3 and the westernmost portion of Segment 2, straddling Highway 57 and extending west to Harbor Boulevard. Although detailed development plans and environmental analyses are not yet available, I obtained the conceptual development plan shown in Figure 5. (See http://hillsforeveryone.org/PDF_Files/aera_proposal.pdf for another version of the conceptual plan, which shows additional roads and features not included on Figure 5.) Drainage 26
Tonner
Bridge
~ 1 km
Figure 5. Conceptual development plan for the Shell-Aera Master Planned Community.

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Although this conceptual plan appears to show approximately half the property as open space, it is clear that this open space represents far less than 50% of the property’s biological value, due to severe fragmentation and edge effects, disruption of movements, and elimination of live-in habitat. Much of the open space would be totally isolated between bubbles of development and roads, such as the open space bubble on the west side of Highway 57. This and other open space patches would be completely isolated from other habitat areas, removing their capacity to support target species and other native wildlife. Moreover, the narrow and highly convoluted bits of open space depicted in this plan would suffer severe edge effects, greatly reducing the area’s ability to support wildlife and ecological processes. As just one example, Argentine ants routinely invade several hundred meters from suburban edges into native scrub habitats, and even farther in moist drainages and canyons (Suarez et al. 1998). The open space bubbles are all less then 1 km across—much less in many places. Consequently, most if not all of the open space depicted in Figure 5 will be invaded by Argentine ants, which eliminate numerous native arthropods, plants, and vertebrates (such as the horned lizard) in a process of ecological collapse already well-documented in Southern California ecosystems (Suarez et al. 1998). In conclusion, only a minor fraction of remaining habitat will remain biologically useful in this proposed development area, and even that would be highly degraded relative to existing conditions.

The conceptual plan appears to be sensitive to wildlife movement needs in its depiction of a continuous “Wildlife Corridor” across the property, from Tonner Bridge through Drainage 26, to the location of the new wildlife tunnel being constructed under Harbor Boulevard. However, this characterization, apparently based on the primary movement corridor across the property as mapped by PCR (2002), is simplistic and biologically misleading. As concluded in the above review of corridor functions, long, narrow gauntlets of “move-through” habitat will not ensure continued functionality of the corridor system, which depends heavily on retaining the large blocks of live-in habitat in the Missing Middle. The mapped open-space corridor is about 4.5 km long and averages less than 500 m wide, which is insufficient to provide reliable live-in habitat for mountain lions and bobcats, for example. This is especially true considering that Segments 4 and 5 are also rather narrow and edge-effected, with marginal capacity to support foraging mountain lions or a subpopulation of bobcats. The overall result would be about 13 km of mostly linear, edge-effected, move-through habitat for these species, from live-in habitat east of Highway 57 to the next reliable foraging or subpopulation area in the Whittier Hills. The likelihood of continued movements by at least bobcats and mountain lions between Tonner Canyon and Whittier Hills would therefore drop dramatically with this development scenario.

In conclusion, this proposed housing development would seriously degrade the ability of Segment 3, and all segments farther west, to continue supporting target species, including mountain lion and bobcat. This would have cascading effects on flora and fauna in segments farther west, especially when considered in context with the relatively small and edge-effected Segments 4 and 5 it connects to on the west. Mule deer populations may, at least temporarily, increase in westerly segments like the Whittier Hills, due to removal of mountain lions from the system. In the short term, this may result in increased car-deer collisions on local roads; but in the long term, even deer are likely to disappear from all segments west of Highway 57 due to isolation of this relatively small population.

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Tres Hermanos Reservoirs
This series of three reservoirs proposed by the City of Industry in Tonner Canyon (Figure 6) would also have substantial adverse impacts on corridor function. The upper Tonner Canyon Proposed City of Industry Road
(approximate alignment)
Olinda
Landfill
SR-57
Tonner Bridge
Figure 6. Aerial photograph showing City of Industry’s proposed Tres Hermanos reservoirs and new road in Tonner Canyon.

ATTACHMENT M
(4 OF 4)
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area (northeast of the Firestone Scout Reservation), although supporting some target species and other wildlife, is mostly open grassland and somewhat degraded in habitat quality. Although a reservoir confined to this upper area would incrementally reduce the size of this segment and its capacity to support target species populations, it is far enough removed from the primary corridor connection across the Missing Middle that it would have less effect on overall corridor function than other developments I considered. However, any development (for reservoirs or other purposes) in middle and especially lower Tonner Canyon could have severe impacts on corridor function, especially if they reduced use of the Tonner Canyon Bridge on Highway 57.

Any development that blocked access to or through the bridge area would make Highway 57 a barrier to wildlife and likely lead to wildlife extirpations in segments farther west.

At the very least, creation of these reservoirs would incrementally reduce the size of what is now a large Chino-Tonner subcore. Tonner Canyon, representing the westernmost portion of this subcore, is the primary source habitat for animals dispersing into the rest of the corridor system to the west. Hence, the location of this project would magnify its relative impact on continued corridor function by increasing the distance wildlife would have to move from source habitat areas to other segments.

Proposed City of Industry Road
Figure 6 also shows an approximate, conceptual alignment for a proposed road parallel to Tonner Canyon (see also Maps 1 and 2). Although I found no specifications for this road or associated development, it would appear to be a major throughway connecting Highway 57 (from the existing Tonner Bridge intersection) to Highway 60 across the widest portion of the PuenteChino Hills Wildlife Corridor. Based on its location, the road would require major cut and fill to construct. Perhaps most troubling is its connection at the critical Tonner Bridge wildlife undercrossing. Depending on design, this is highly likely to render this last remaining corridor connection non-functional for mountain lion, deer, bobcat, and numerous other species. Even if this connection could be engineered to retain a functional wildlife undercrossing, the road could severely impact wildlife populations and movements along a broad front. A series of additional undercrossings (or overcrossings) and extensive wildlife fencing would need to be incorporated along the length of the road, or else most of Tonner Canyon would be isolated between two barrier roads (this one and Highway 57) or wildlife would suffer severe roadkill impacts.

Approximately 21.2 sq. km of grasslands, forests, and shrublands would be segregated from the large and valuable Chino-Tonner subcore, incrementally diminishing its capacity to support wildlife populations. At best, what is now a broadly contiguous block of habitat would be reduced to a narrow and more edge-effected funnel across the Olinda Landfill to the Tonner Bridge.

Cumulative Effects
A full impact analysis for any or all of these proposed projects would need to address cumulative impacts on wildlife populations and movements through the corridor, which is beyond the scope of this report. Among these cumulative impacts would be inducement of further development, Puente-Chino “Missing Middle” Analysis
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such as additional residential, commercial, or industrial development along the road. Increased traffic (and hence roadkill) would also need to be analyzed and mitigated for. Any combination of two or more of these projects would likely render the Puente-Chino Hills Wildlife Corridor non-functional west of Olinda Landfill, regardless of mitigation.

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Discussion
Before summarizing conservation and restoration recommendations for the Missing Middle, this section reviews the literature on the functions and benefits of wildlife corridors in conservation, including criticisms of corridor conservation.

Functions and Benefits of Wildlife
Corridors
Landscape linkages and wildlife movement
corridors vaulted to the forefront of conservation
thinking in recent decades, in response to rising recognition that habitat fragmentation is a principal cause of species extinction and endangerment (Willis 1974, Diamond 1975, Wilson and Willis 1974, Noss 1983, Wilcox and Murphy 1985, Forman 1991, Harrison 1992, Rosenberg et al. 1997). Habitat connections or movement corridors connecting reserves or larger “core areas” of habitat are thought to counter many adverse effects of isolation by fragmentation on species and ecological processes (Preston 1962, Noss 1983, 1987, Soulé 1991, Meffe and Caroll 1994, Rosenberg et al. 1997, Soulé and Terborgh 1999, Beier et al. in press). Although some critics have argued that there are costs as well as benefits to conserving corridors, and that under certain circumstances creating or maintaining corridors could even harm some species or communities (e.g., Simberloff and Cox 1987, Simberloff et al. 1992, Hess 1994), the overwhelming weight of scientific evidence is that maintaining connectivity is generally beneficial, especially for those species and ecological communities for which connectivity “is the natural state of things” (Soulé and Terborgh 1999). Certainly, for most species and ecological communities, maintaining connectivity is less risky than losing connectivity (Hobbs 1992, Beier and Noss 1998, Soulé and Terborgh 1999).

Assessing Connectivity Pros and Cons
This section reviews specific arguments for and
against conserving corridors and how they apply to the
Puente-Chino Hills. As elaborated below, in most
cases, arguments against corridor conservation are
really just cautions against applying corridors as a
panacea for conservation, in recognition that there may be special cases where connecting reserves could cause more harm than good or where other approaches to conservation may be more effective or cost-effective (for example, enlarging core reserves rather than connecting existing reserves). These special cases do not apply to the Puente-Chino Hills Wildlife Corridor, where maintaining connectivity would clearly provide net benefits for biological diversity and ecosystem health in these hills. Given that the weight of scientific evidence favors connectivity here, whether and how connectivity can be assured is a societal issue not addressed in this scientific treatment. “Those who would destroy the
last remnants of natural
connectivity should bear the
burden of proving that corridor
destruction will not harm target
populations.”
Paul Beier & Reed Noss (1998)
“Connectivity is not just another
goal of conservation: it is the
natural state of things.”
Michael Soulé & John Terborgh (1999)
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The potential disadvantages of creating or maintaining wildlife movement corridors include several ecological arguments and one financial argument (Simberloff and Cox 1987, Simberloff et al. 1992, Hobbs 1992, Hess 1994):

1. Corridors may serve as conduits for the spread of deleterious species, like invasive pests, weeds, or predators.

2. Corridors may serve to spread detrimental processes—such as wildfire or disease—to or among reserve areas.6

3. Corridors may facilitate movements by highly mobile animals between reserves even without corridors. (Or, these species may be overly abundant in urban interface areas due to imbalanced ecological conditions.) But corridors may not help movement for more sedentary or at-risk species, for which other conservation approaches may work better than corridors.

4. Corridors could act as population “sinks” (Pulliam 1988), attracting individuals from higher quality habitat areas into edge-effected habitats where death rates exceed birth rates. If this effect is strong enough, it can reduce the regional abundance of the species, or even increase extinction probabilities for a rare species.

5. Corridors may be expensive to create or maintain and may not represent the optimal allocation of limited funding relative to, for example, increasing the size or management of existing core areas.

Note that in one way or another, all of these potential disadvantages hinge on relative comparisons of potential risks and benefits of maintaining vs. losing connectivity. Also, as pointed out by numerous researchers, the risks and benefits of corridors will vary by species. In the sections below, I briefly evaluate these potential disadvantages as they may apply within the Puente-Chino Hills Wildlife Corridor for target species of interest.

Conduits for Deleterious Species
It is difficult to envision how any deleterious species might increase its distribution or adverse effects due to conserving additional lands in this existing archipelago of open space reserves.

Connecting these areas with additional conservation would not increase rates with which annual weeds, Argentine ants, rats, house mice, or other potential pest species invade open space areas relative to existing conditions. Sources of such deleterious species are nearly ubiquitous in Southern California, due to existing human land use patterns. Maintaining an existing open space corridor system would not facilitate expansions of such species, either from the more urbanized western portions of the study area into the Santa Ana Mountains, or vice versa, and may even help counter further invasions (relative to more roads or development in the area).

6 Although wildfire and disease are natural disturbance processes in ecosystems, changes wrought by humans, such as habitat fragmentation and increased fire frequencies in urban interface areas, may create situations where these natural processes cause unnatural harm to biological resources. Corridors could help spread these deleterious effects.

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Conduits for Deleterious Processes
Again, it is difficult to conceive how maintaining connectivity in this context could contribute to the spread of deleterious processes. This argument is generally based on the assumption that a new corridor is being created (e.g., connecting what are naturally unconnected habitat areas) rather than maintaining “the natural state of things” with an existing, natural corridor (Beier and Noss 1998). As with the argument concerning deleterious species, this seems not to be an issue for the Puente-Chino Hills Wildlife Corridor. Although diseases or parasites may be carried between habitat segments by wildlife, this already occurs and always did. Although fires may spread from one segment to another under certain conditions, the area is already highly segmented by fire breaks in the form of existing roads and other discontinuities. In fact, given the nature of Southern California’s most destructive wildfires, which are driven by Santa Ana wind conditions (Keeley and Fotheringham 2001, Keeley et al. 1999, Halsey 2004), fire provides a stronger argument for not building more homes in wildland areas, rather than an argument for not conserving wildland areas.

Ineffectiveness for Rare or Sedentary Target Species
This is clearly a non-argument for the Puente and Chino Hills. Target species selected for review in this report, including both rare and common species, are highly sensitive to habitat fragmentation and benefit from corridor conservation (e.g., Beier 1993, Beier et al. in press, Crooks 2002, Ng et al. 2004). Although some rare or more sedentary species may not benefit directly from corridor conservation here (e.g., some reptile and amphibian species already lost from western segments of the corridor), the ecological benefits that accrue from corridor conservation for the remaining flora and fauna are indisputable. Indeed, research in the PuenteChino Hills Wildlife Corridor reinforces other research indicating that more common, insensitive, and “pesky” wildlife like skunks and raccoons actually increase in density with reductions in larger carnivores like mountain lions and bobcats, due to losses of landscape connectivity (Haas 2000, Crooks and Soulé 1999). Countering this process of “meso-predator release” (Crooks and Soulé 1999), and the cascade of species losses and other adverse ecological changes that it can bring, is a strong argument for maintaining the Puente-Chino Hills Wildlife Corridor for mountain lions, coyotes, and bobcats.

Population Sinks
This is a legitimate argument that deserves analysis. It may be that, especially for species highly prone to roadkill, mortality in the Puente and Chino Hills is elevated relative to larger, more contiguous areas like the Santa Ana Mountains. It is conceivable that the corridor therefore serves as a “population sink” (Pulliam 1988), where animals enter the corridor from larger or higher quality habitats, only to be killed. However, the potential for this effect to substantially reduce regional wildlife populations in the Santa Ana Mountains seems remote. Moreover, the benefits of these species living within the Puente and Chino Hills, even with elevated mortality rates, are immense, both to ecological health and to quality of life for local human residents.

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Suboptimal Conservation Investment
This is a non-argument for this study area. Given the current wildland-development pattern that exists, there is no alternative to corridor conservation and restoration for retaining species populations and maintaining healthy ecological processes in this area. Although one could argue that further investment in conserving these hills could be better spent elsewhere (e.g., enlarging larger wilderness reserves in Southern California mountains), this would come at the detriment of maintaining a unique ecological classroom full of wildlife in close proximity to millions of people craving a connection with nature. According to the California Department of Parks and Recreation, nearly a quarter billion dollars have already been spent on open space conservation in the Puente and Chino Hills, and this investment could be for naught if additional conservation fails to secure a continuous corridor from the Santa Ana Mountains to the Whittier Hills.

Mitigating Road Effects
Roads or the traffic they carry kill animals directly
(roadkill), disrupt natural migration and movement
patterns, interfere with species communication, change
water runoff and flow patterns, and create air, water, and soil pollution (Trombulak and Frissell 2000, Forman and Deblinger 2000, Jones et al. 2000, Reijnen et al. 1997). During Beier’s (1993, 1995) study of mountain lions in the Santa Ana Mountains, vehicles killed 33% of the population, including four lions killed at one road-crossing during a 2-year period.

The growing awareness of road impacts on environmental health and imperiled species has created a burgeoning literature on efforts to mitigate these effects with improved wildlife roadcrossing structures. Wildlife crossing structures have proved successful in the United States and elsewhere (Transportation Research Board 2002). The main types of structures, from most to least effective, are vegetated land-bridges, bridges, underpasses, and culverts.

About 50 vegetated wildlife overpasses, ranging from 50 m (164 ft) to over 200 m (656 ft) wide, have been built in Europe, Canada, and the U.S. (Evink 2002, Forman et al. 2003). Soil (0.5 to 2 m deep) covers the overpasses, which are planted, usually with native vegetation (Jackson and Griffin 2000). Overpasses are quieter than underpasses and maintain ambient conditions (Jackson and Griffin 2000), so they may be less intimidating for some species than dark tunnels.

In Banff Provincial Park, large mammals preferred overpasses to other crossing structures (Forman et al. 2003). Similarly, birds, butterflies, and other open-air wildlife are more likely to use overpasses than underpasses.

Bridges are also effective crossing structures, especially if wide enough to permit growth of both riparian and upland vegetation along stream banks (Jackson and Griffin 2000, Evink 2002, Forman et al. 2003). Bridges with greater openness ratios are generally more successful than low bridges and culverts (Veenbaas and Brandjes 1999, Jackson and Griffin 2000). The Tonner Bridge is a good example of a broad, open bridge with natural vegetation beneath. My observations reinforce those of previous biologists that maintaining access through this structure, “Nothing is worse for sensitive
wildlife than a road.”
Reed Noss
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and perhaps improving habitat conditions on either side, is critical to the flow of large mammals across the Puente-Chino Hills landscape.

Although inferior to bridges, culverts and other tunnel-like structures can be effective for some species (Jackson and Griffin 2000). Only very large culverts (such as box culverts and equestrian tunnels) are effective for large mammals (Lyren 2001, Haas 2000, Gloyne and Clevenger 2001). Gloyne and Clevenger (2001) suggest that underpasses for ungulates should be at least 4.27 m high and 8 m wide, with an openness ratio of 0.9 (where the openness ratio = height x width/length). Earthen flooring is preferable to concrete or metal (Evink 2002).

In places where a bridged, vegetated under-crossing or over-crossing is not feasible, placing pipe culverts alongside box culverts can help serve movement needs of both small and large animals.

Special crossing structures that allow light and water to enter the structure have been designed to accommodate amphibians.

Noise, artificial night lighting, traffic noise, and other disturbances can deter animal use of a crossing structure (Yanes et al. 1995, Clevenger and Waltho 1999, Forman et al. 2003). Shrub or tree cover can help funnel wildlife to a passage while hiding them or making them feel more secure when approaching crossing structures (Evink 2002, Forman et al. 2003). Regardless of crossing type, wildlife fencing is necessary to funnel animals towards road-crossing structures and keep them off the road surface (Falk et al. 1978, Ludwig and Bremicker 1983, Feldhammer et al. 1986, Haas 2000, Lyren 2001, Forman et al. 2003). Earthen one-way ramps can allow animals that wander into the right-of-way to escape over the fence (Bekker et al. 1995, Forman et al. 2003).

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Conclusions and Recommendations
Conservation and Restoration Priorities for the Missing Middle Based on the analysis of corridor function, Map 3 shows locations of priority conservation and restoration actions in and near the Missing Middle. This is by no means a comprehensive summary of all necessary and sufficient actions to maintain or improve biological conditions throughout the Puente-Chino Hills landscape. Rather, it focuses on those locations and actions that seem most critical to maintaining functional connectivity across the Puente-Chino Hills Wildlife Corridor based on the metapopulation analysis.

These recommendations are redundant with those from previous studies, especially concerning the need to secure and improve unimpeded movement by large target species across roads. This should not be surprising, because information on the characteristics and functioning of these corridor segments is quite consistent across studies. Perhaps the greatest benefit of the metaanalysis provided in this report is a renewed focus on the need to conserve not just unimpeded movement, but an archipelago of relatively large habitat blocks with sufficient carrying capacity to ensure continued presence of viable populations through this range of hills. Road-crossings are just one part of the story.

Priority Conservation Lands
Conserving intact habitat blocks within the red-hatched lands on Map 3 is essential to maintaining functional metapopulation dynamics for target species throughout the Puente-Chino Hills Wildlife Corridor. As supported by the geographic unit analysis, the capacity of Segments 2 and 3—from Chino Hills State Park to Harbor Boulevard—to support robust populations of target species and live-in habitat for mountain lions is essential to keeping these species in the study area, all the way to Whittier Hills. Essentially all of the Shell-Aera property, and at least the lower 1/2 to 2/3 of the City of Industry lands in Tonner Canyon, are of high priority for conservation.

Note that the line separating high-priority conservation lands in mid- to lower Tonner Canyon from upper Tonner Canyon is somewhat arbitrary. But the farther up Tonner Canyon one goes, the less essential habitat becomes for ensuring corridor functionality. (Note, however, that Cooper [2000] considered upper Tonner Canyon a high conservation priority for native birds, especially grassland species like raptors and grasshopper sparrows.) I established the northeast boundary of the Tonner Canyon high-priority conservation area primarily to consolidate a contiguous reserve along with the existing Firestone Scout Reservation and Chino Hills State Park. Extending this boundary farther north would increase biological benefits even more, but with decreasing marginal returns for corridor function.

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Map 3. Conservation and restoration priorities in the vicinity of Missing Middle.

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Essentially all of the Shell-Aera property west of Highway 57 is extremely high priority for conserving corridor integrity. Based on metapopulation analysis, conserving a “move-through corridor” across this property, as depicted in Figure 5, is not enough to ensure continued target species presence through the corridor system. Given this segment’s location between two nearbarrier roads, and the relatively narrow and constrained status of Segments 4 and 5 to the west, securing a large, intact habitat block capable of supporting populations or subpopulations of target species is essential here. Moreover, this segment could benefit greatly from habitat management and restoration to increase carrying capacity for target species, and thereby to decrease the probability of species extirpations here and all the way to the Whittier Hills.

Priority Crossing Improvements
Map 3 shows five priority road-crossing improvements with magenta circles, labeled A through E from east to west. Most of these recommendations have already been made by others (e.g., Haas 2000), and some may already have been acted on or are in planning stages. At the risk of redundancy, I nevertheless recommend the following improvements in these general locations.

Refer to Haas (2000) for additional recommendations and details:

A. Add wildlife fencing on either side of Carbon Canyon Road to reduce roadkill and encourage wildlife to use existing culverts, especially the concrete box culvert near the entrance to Chino Hills State Park. Adding another wildlife crossing structure, designed to accommodate all large mammals, would be even better. Given that traffic on this 2- lane road is increasing due to increasing development in the vicinity (Haas 2000), any future road upgrades should incorporate bridges or other very open wildlife crossing structures as mitigation. A variety of smaller under-crossings with funneling fences, specifically designed to accommodate smaller reptiles, amphibians, and mammals, should also be considered to improve connectivity for these species.

B. Prohibit any development that would increase traffic under the Tonner Bridge or add any new impediments (structures, lights, noise, etc.) to the vicinity of the bridge. Restore riparian vegetation along Tonner Creek, where degraded by oil development activities.

Fence along Highway 57 if monitoring suggests road mortality is high.

C. A wildlife underpass tunnel is to be constructed here under Harbor Boulevard, but recommended fencing has apparently not been allowed by a property owner (A.

Henderson, personal communication). Secure rights to install wildlife fencing along both sides of Harbor Boulevard to reduce roadkill and ensure maximum utility of the wildlife tunnel. Plant native shrubs and trees on either side of the tunnel to provide cover to wildlife approaching the entrances. Consider adding smaller under-crossings and funneling fences to accommodate smaller reptiles, amphibians, and mammals.

D. Secure remaining “at-risk” parcels in this narrow, constricted portion of the corridor, west of Powder Canyon and Schabarum Regional Park. Enlarge or otherwise improve the existing equestrian tunnel to enhance its use by wildlife, including adding screening Puente-Chino “Missing Middle” Analysis
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vegetation, especially on the western end. Fence either side of the tunnel to help funnel wildlife to it. However, extensive fencing along Hacienda Boulevard is not recommended, because most large mammals currently cross at-grade. Although Hacienda Boulevard currently has moderate traffic at relatively low speeds, and therefore relatively low roadkill (Haas 2000), road improvements or increases in traffic could make the situation worse. In this case, consider building a wildlife overpass (a vegetated wildlife bridge) over Hacienda Boulevard, taking advantage of steep slopes rising up from either side of the road. Given this terrain, a vegetated overpass somewhere between Skyline Drive and the equestrian tunnel may be feasible and would certainly be superior to culverts or other underpass structures in accommodating wildlife movement. Consider also adding smaller under-crossings and funneling fences to accommodate smaller reptiles, amphibians, and mammals.

E. Maintain and improve the Colima Service Tunnel as a critical wildlife underpass. Add fencing or screening vegetation, if necessary, based on further site-specific inspection or monitoring. Limit and mitigate for any actions that may increase traffic, light, noise, or human activity in the vicinity of the Service Tunnel from sunset to sunrise, when wildlife use is most frequent. Consider also adding smaller under-crossings and funneling fences to accommodate smaller reptiles, amphibians, and mammals.

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Attachment A. Revised Appendix H, Transportation and Vehicle Miles Traveled (VMT) Impact Analysis

ATTACHMENT E
(2 OF 2)
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April 2026

CITY OF BREA FOCUSED

GENERAL PLAN UPDATE AND
BREA CORE SPECIFIC PLAN:

TRANSPORTATION AND VEHICLE

MILES TRAVELED (VMT)

IMPACT ANALYSIS

BREA, CA
Oakland, California
Inside front cover.

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City of Brea Focused General
Plan Update and Brea Core
Specific Plan: Transportation
and Vehicle Miles Traveled
(VMT) Impact Analysis
Brea, CA
Prepared for:

De Novo Planning Group
180 East Main Street, Suite 108
Tustin, CA 92780
Prepared by:

Kittelson & Associates, Inc.
750 The City Drive South, Suite 410
Orange, CA 92868
Project Principal:

Tim Erney
Senior Principal Planner
Project Number 29637
April 2026
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CONTENTS
Executive Summary ........................................................................................................................ 2 Significant Transportation Impacts............................................................................................ 2 Introduction..................................................................................................................................... 4 Project Description...................................................................................................................... 4 Existing Conditions .......................................................................................................................... 6 Roadway Network ...................................................................................................................... 6 Transit Service .............................................................................................................................. 8 Bicycle Facilities......................................................................................................................... 11 Pedestrian Facilities................................................................................................................... 13 Freight/Goods Movement........................................................................................................ 19 Regulatory Setting ........................................................................................................................ 22 State Regulations ...................................................................................................................... 22 Regional Regulations................................................................................................................ 24 Local Regulations and Plans.................................................................................................... 26 Transportation Impact Analysis ................................................................................................... 30 Analysis Scenarios, Methodologies, and Modeling Approach ............................................ 30 Existing Vehicle Miles Traveled.................................................... Error! Bookmark not defined.

Significant Impact Thresholds................................................................................................... 31 Item 1: VMT ................................................................................................................................ 32 Item 2: Transit, Roadway, Bicycle, and Pedestrian Facilities................................................. 34 Item 3: Geometric Design and Incompatible Use Hazards .................................................. 36 Item 4: Emergency Access....................................................................................................... 37 Conclusions ................................................................................................................................... 40 Significant Transportation Impacts............................................. Error! Bookmark not defined.

City of Brea Focused General Plan Update And Brea Code Specific Plan: Transportation and Vehicle Miles Traveled (VMT) Impact Analysis
April 2026
Kittelson & Associates

LIST OF FIGURES
Figure 1: Existing Transit Service in Brea....................................................................................................................10 Figure 2: Existing Bikeway Network...........................................................................................................................12 Figure 3: 2003 General Plan Focus Areas and Brea Core......................................................................................14 Figure 4: Sidewalk Gaps in Brea Core Area ............................................................................................................18 Figure 5: Existing Truck Routes...................................................................................................................................20

LIST OF TABLES
Table 1: Transit Service in Brea....................................................................................................................................9 Table 2: Brea City Shuttle and Van Service...............................................................................................................9 Table 3: Existing Truck Routes....................................................................................................................................19 Table 4: Citywide VMT per Service Population Analysis.........................................................................................32 Table 5: Link-Level Boundary Citywide VMT per Service Population Threshold...................................................33 Table 6: VMT per Service Population Threshold for the Brea Core Specific Plan ................................................33

APPENDICES
Appendix 1 — VMT Technical Data
Section 1 — Executive Summary
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EXECUTIVE SUMMARY
The City of Brea is in the northeastern corner of Orange County, where the boundaries of Orange, Los Angeles, and San Bernardino Counties converge. The City is bordered by unincorporated Orange County land and the Los Angeles County line to the north; Chino Hills State Park and the San Bernardino County line to the east; the Cities of Yorba Linda, Placentia, and Fullerton to the south; and the City of La Habra to the west. The Orange Freeway (State Route [SR] 57) bisects the City from north to south. The three major east–west roadways are Imperial Highway (SR 90), Carbon Canyon Road (SR 142), and Lambert Road The City is preparing the Focused General Plan Update, which will introduce a Mobility Element (replacing the existing Circulation Element) addressing active transportation, complete streets, automobile and truck traffic, intersection and roadway vehicular level of service (LOS) operations, and transit options for communities reliant on public transportation. The Focused General Plan will serve the City through 2050.

The Plan proposes a mix of uses. Within the planning, buildout of the proposed General Plan Land Use Element could yield a total of up to 23,736 housing units, a population of 67,647 people, approximately

30.59 million square feet of non-residential square footage, and 73,709 jobs. This represents development growth above existing development conditions of approximately 7,390 new housing units, 21,062 people,

9.1 million square feet of new non-residential square footage, and 21,772 jobs.

Kittelson & Associates (“Kittelson”) has prepared a transportation analysis of the Plan. Below is a summary of results of the transportation analysis conducted for the Plan, including any significant impact findings and recommended improvements.

SIGNIFICANT TRANSPORTATION IMPACT

FINDINGS
The California Environmental Quality Act (CEQA) transportation impact analysis of the General Plan Update determined that impacts would be less than significant for the following topics:
 Vehicle miles traveled (VMT)
 Transit, roadway, bicycle, and pedestrian facilities
 Geometric design and incompatible use hazards
 Emergency access
Section 2 — Introduction
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INTRODUCTION
This report documents the California Environmental Quality Act (CEQA) transportation assessments for the Brea Focused General Plan Update and Brea Core Specific Plan, and summarizes the methodology, findings, and conclusions of the analysis.

PROJECT DESCRIPTION
The City of Brea is 12.4 square miles in northern Orange County, California. The city is bordered by the City of La Habra to the west, the City of Fullerton to the southwest, the City of Placentia to the south, Yorba Linda to the east, and Daimond Bar to the north. The City is preparing the Focused General Plan Update, which will introduce a Mobility Element (replacing the existing Circulation Element) addressing active transportation, complete streets, automobile and truck traffic, intersection and roadway vehicular level of service (LOS) operations, and transit options for communities reliant on public transportation. The Focused General Plan will serve the City through 2050.

Note that this study examines citywide buildout estimates that represent a hypothetical scenario of development in the City. Based on historical development patterns in Brea, it is likelier that development would occur at levels lower than the buildout estimate, due to factors such as standards governing density and floor area ratio, and physical factors such as topography.

Section 3 — Existing Conditions
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EXISTING CONDITIONS
This section summarizes existing mobility conditions in the City of Brea related to vehicles, transit, bicycles, pedestrians, freight/goods movement, and traffic operations.

ROADWAY NETWORK
The roadway network in the City contains three state routes: State Route 57 (SR 57), Imperial Highway (SR 90), and Carbon Canyon Road-Valencia Avenue (SR 142). These routes, along with other significant roadways, in the City, are described below.

STATE ROUTE 57 FREEWAY
State Route 57 (SR 57) is a facility under Caltrans’ jurisdiction that serves as a significant north-west linkage between Los Angeles County and Orange County, connecting with Interstate 5 (I-5) and State Route 22 (SR-22) to the south and Interstate 210 (I-210), Interstate 10 (I-10) and State Route 60 (SR 60) to the north.

Within Brea, SR 57 is a 12-lane freeway with six lanes in each direction with a speed limit of 65 miles per hour.

In Brea, SR 57 has interchanges at Lambert Road, Imperial Highway, and Tonner Canyon Road.

IMPERIAL HIGHWAY
Imperial Highway (SR 90) is classified as a major arterial within Brea, carrying significant vehicle volumes in an east-west direction. Imperial Highway primarily supports through-traffic with access to multiple residential and commercial destinations. With a speed limit of 40 miles per hour, it features two to three travel lanes on each side of the street, primarily divided by a center turn lane. All major intersections along Imperial Highway have pedestrian crosswalks and pedestrian signal heads; in addition, sidewalks are provided along the corridor. Additionally, Imperial Highway is designated as a Smart Street within the MPAH. A “Smart Street” includes various traffic-carrying capacity enhancements to facilitate traffic flow. In particular, modifications to Imperial Highway included restriping from four to six lanes, modification of medians at intersections, addition of bus pads and turnouts, and re-timed traffic signals to improve coordination.1 These modifications help to address traffic congestion and improve operations on the road.

CARBON CANYON ROAD
Carbon Canyon Road (SR 142) is under Caltrans’ jurisdiction and is classified as a primary arterial from Valencia Avenue to Brea Hills Avenue, and as a collector from Brea Hills Avenue east to the city and county boundary. The roadway travels in the east-west direction and provides direct access to Olinda Village and cities to the east such as Chino Hills, Chino, and Eastvale. The roadway is rural in character, with one lane in each direction and no center divider. The roadway does not offer consistent pedestrian crosswalks as there is little pedestrian demand.

VALENCIA AVENUE
Also classified as SR 142, Valencia Avenue is under Caltrans’ jurisdiction between Lambert Road / Carbon Canyon Road and Imperial Highway (SR 90). This portion is classified as a primary arterial. The roadway travels in the north-south direction and provides a link between northeast and southeast Brea, as well as to the City of Placentia in the south. Valencia Avenue is a four-lane divided roadway for much of its length and features continuous sidewalks along the east side of the roadway, with sporadic sidewalks on its west side. The roadway includes pedestrian crosswalks at every signalized intersection. 1 OCTA, “Destination 2035”, Detailed Year 2035 Baseline Project List, 2010 City of Brea Focused General Plan Update And Brea Code Specific Plan: Transportation Impact Analysis April 2026 Existing Conditions
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BREA BOULEVARD
Brea Boulevard is classified as a primary arterial crossing the City in the north-south direction. This roadway accommodates a combination of uses, including commercial and mixed-use areas with a speed limit of 40 miles per hour. It features two travel lanes on each side of a median along with a left-turn lane at multiple locations. On-street parking spaces are available in most parts of this roadway. All major intersections along Brea Boulevard have pedestrian crosswalks and pedestrian signal heads; in addition, there are sidewalks along the corridor.

LAMBERT ROAD
Lambert Road is classified as a major arterial crossing the city in the east-west direction. This roadway primarily supports through-traffic with a speed limit of 40 miles per hour. It features two to three travel lanes on each side of the street alternating between a median and a center turn lane. Several intersections along Lambert Road have pedestrian crosswalks and pedestrian signal heads; in addition, there are sidewalks along the corridor.

OTHER KEY ROADWAYS
Other arterial roadways in Brea include State College Boulevard, Central Avenue, Puente Street, and Birch Street. Collector streets include Elm Street, Palm Street, Whittier Avenue, Sante Fe Road, and Placentia Avenue.

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TRANSIT SERVICE
Public transit service in Brea is provided by fixed-route bus service operated by Orange County Transportation Authority (OCTA) and Foothill Transit, plus local services provided by the City of Brea. All bus routes that run operate within the City provide service to the Brea Mall Transit Center, located off State College Boulevard between Imperial Highway and Lambert Road.

OCTA is the major transit agency serving Orange County, with services including fixed-route buses and paratransit. It provides approximately 51 fixed bus routes, including local, community, rapid, and StationLink services on a countywide basis. OCTA bus network spans most of Orange County, connecting major cities, employment centers, transit hubs, and points of interest. OCTA provides connections to other municipalities and the rest of the region through transit nodes and other intermodal hubs. Systemwide, buses generally operate on 15 to 30-minute intervals during peak hours, with less frequent service during off-peak times and on weekends.

Currently, there are four OCTA bus routes that operate within the City of Brea2:
/ Route 57 which operates between Brea and Newport Beach. / Route 59 which operates between Brea and Irvine
/ Route 129, a community route that operates between Brea and Buena Park. / Route 143, which operates from La Habra to Brea.

In addition, OCTA's ACCESS paratransit service serves those with disabilities.

Foothill Transit operates a fleet of over 300 buses throughout Southern California’s San Gabriel Valley and Pomona Valley. Within Brea, Foothill Transit operates one route, typically on a one-hour schedule:
/ Route 286 which runs between Pomona and Brea.3
In addition to the routes provided by OCTA and Foothill Transit, the City of Brea provides local transportation services. The City offers free shuttle transportation for seniors, providing rides to the Senior Center and scheduled shopping trips. The shuttle operates Monday to Friday, requiring applicants to be 60+ years old and Brea residents. Reservations for rides must be made one business day in advance. The shuttle offers morning pick-ups between 8:15 AM and 10:00 AM. and return options after lunch. Scheduled shopping trips to various stores are available on specific days. Additionally, a new van service called “Seniors on the Go!” operates Tuesday to Friday offering rides for personal errands and community visits within Orange County for a small fee.4
2 Orange County Transportation Authority, “Routes and Schedules”, last accessed April 2026. https://www.octa.net/getting-around/bus/oc-bus/routes-and-schedules/routes-and-schedules 3 Foothill Transit, “Schedules and Maps”, last accessed May 2024. https://www.foothilltransit.org/buslines/timetables
4 City of Brea, “Transportation”, last accessed December 2025. https://www.cityofbrea.gov/1105/Transportation
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Table 1 and Table 2 summarize the transit service in Brea and Figure 1 illustrates the routes.

Table 1: Transit Service in Brea
Route Route Type Operator Route Description
OCTA Route 57
Brea- Newport
Beach
Local Fixed
Route
OCTA Travels from Brea to Newport Beach via State
College Boulevard / Bristol Street.

OCTA Route 59
Brea - Irvine
Local Fixed
Route
OCTA Travels from Brea to Irvine, stopping at the Brea
Mall Area, via Birch Street / Kraemer Boulevard /
Glassell Street / Grand Avenue / Von Karman
Avenue.

OCTA Route 129
Brea – Buena Park
Community
Route
OCTA Travels from Brea and Buena Park via Artesia
Boulevard / Beach Boulevard / La Habra Boulevard
/ Brea Boulevard / Birch Street.

OCTA Route 143
La Habra - Brea
Community
Route
OCTA Travels from La Habra to Brea via Whittier
Boulevard / Harbor Boulevard / Brea Boulevard /
Birch Street.

Foothill Route 286
Brea - Pomona
Community
Route
Foothill
Transit
Travels from Brea to Pomona via Diamond Bar
Boulevard / W Mission Boulevard / S Garey Avenue.

Sources: OCTA, and Foothill Transit (information accessed April 2026) Table 2: Brea City Shuttle and Van Service
Route Route Type Operator Route Description
Brea Senior Center
Shuttle
City Shuttle City of Brea Free shuttle transportation from the Senior Center to pre-scheduled shopping. Monday to Friday.

Local Scheduled
Shopping Trips
City Shuttle City of Brea Mondays, 12:45 PM – Walmart Shopping First Wednesday of the month 12:45 PM –
Ralphs/Rite Aid Shopping
Third Wednesday of the month, 12:45 PM –
Albertsons/Trader Joe’s Shopping
Seniors on the Go! City Van
Service
City of Brea For $2 one way and with a ride reservation, with a cap of 5 miles, this service can take Brea residents
ages 60 and over where they need to go.

Operates Tuesday to Friday from 9:00 AM to 12:30
PM.

Source: City of Brea (information accessed May 2024)
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Figure 1: Existing Transit Service in Brea
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BICYCLE FACILITIES
The California Department of Transportation (Caltrans) classifies and defines bicycle facilities. Caltrans designates four classes of bicycle facilities: Classes I, II, III, and IV. The illustration below illustrates and describes the bicycle facility classifications.

Existing bikeways in the City are shown in Figure 2.

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Figure 2: Existing Bikeway Network
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PEDESTRIAN FACILITIES
Throughout the City pedestrian facilities include crosswalks, pedestrian crossing signals, lighting, street trees, and curb ramps. The pedestrian network is comprised of sidewalks and multi-use paths, allowing residents to walk to their destination along dedicated paths and reducing conflicts with other travel modes. Routes to major destinations, such as schools and public facilities, attract youth and are important within the pedestrian network. Throughout the City, opportunities exist to improve sidewalk connectivity, installing pedestrian crossings, and maintaining consistency with pedestrian amenities.

Sidewalks are generally included on most roadways within the City; however, there are gaps in some of the industrial areas of Brea. At locations where sidewalks are provided, the City’s Municipal Code requires sidewalks to be a minimum of 4 feet wide in residential areas, and a minimum of 5 feet wide in a commercial or industrial area, with additional ADA, curb-ramp and curb requirements.

The following is an overview of the typical pedestrian facilities across the City, separated by the surrounding land uses and land use patterns. This examination encompasses a diverse array of areas, providing information on the accessibility and infrastructure designed to facilitate pedestrian movements throughout these specific locales. This section describes pedestrian facilities along roadways, summarized within the City’s focus areas as defined in the 2003 Brea General Plan and as proposed through the new Brea Core Specific Plan, which are listed below and shown in Figure 3. / Northwest Neighborhoods
/ Carbon Canyon and Olinda Village
/ Hillsides and Unincorporated Brea
/ Southeast Brea
/ Brea Core Area (which includes portions of Historic Brea and Downtown Brea delineated in the 2003 General Plan
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Figure 3: 2003 General Plan Focus Areas and Brea Core
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NORTHWEST NEIGHBORHOODS
The northwest area of Brea contains a mix of residential neighborhoods, including several senior housing developments. Most of the homes were built between the 1950s and 1970s, with some newer tracts built in the 1980s and 1990s. The neighborhoods typically feature sidewalks on both sides of the roadway, with occasional sections that lack sidewalks. Pedestrian amenities are provided along the sidewalks such as curb ramps. Streetlights can be found throughout the area and are consistently spaced throughout.

Puente Street Candlewood Street

CARBON CANYON AND OLINDA VILLAGE
Carbon Canyon and Olinda Village have less developed pedestrian infrastructure. Olinda Village is a distinct residential neighborhood within Carbon Canyon. The rural character of the area, together with the development constraints imposed by topography, geologic conditions, and the configuration of Carbon Canyon Road limit land use opportunities within Carbon Canyon. The majority of Carbon Canyon Road does not contain sidewalks and crosswalks. Pedestrian travel occurs along the paved roadway shoulder or unpaved sections. Although there are few pedestrian crossings and signage in rural areas, the rural setting lacks sufficient streetlights and pedestrian-friendly lighting.

Olinda Village Carbon Canyon Road
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HILLSIDES AND UNINCORPORATED BREA
The hillsides and unincorporated Brea area refer to pockets of land where the uses are currently undeveloped and include some areas north of Lambert Road up to the Los Angeles County border.

Roadways in these areas do not contain sidewalks or crosswalks, with limited pedestrian demand.

Brea Canyon Road Valencia Ave

SOUTHEAST BREA
Southeast Brea includes the former oil-use related and agricultural properties that have since transitioned to residential uses. Many of these residences are part of La Floresta, a master-planned community. La Floresta has a well-developed pedestrian network with complete sidewalk connectivity, landscaping, crosswalks, and curb ramps.

La Floresta Street Terrazo Drive
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BREA CORE AREA
In the Brea Core Area specifically, sidewalks exist along the majority of roadways. Few gaps in the sidewalks currently exist, such as portions of Lambert Road, Berry Road, and State College Boulevard, as highlighted in Figure 4. These gaps are small and typically occur in industrial areas that tend to have lower pedestrian demand, and some gaps occur only along one side of the street, with sidewalk connectivity available on the other side. In addition, several streets that encircle the Brea Mall are missing sidewalks. Similarly, there are gaps in lighting and crossing infrastructure in the Plan Area, as many sidewalks do not provide pedestrian buffers, such as street trees and landscaping, which improve perceived safety.

Within the Brea Core Area, multiple intersections have high visibility crosswalks, including most intersections along Imperial Highway, indicating a unique place and high pedestrian volumes.

Poplar Avenue Birch Street
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Figure 4: Sidewalk Gaps in Brea Core Area
Source: Kittelson and Associates, 2024
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FREIGHT/GOODS MOVEMENT
Freight and goods movement utilize several of the major routes in the City’s network. As illustrated in Figure 5, trucks move along Central Avenue, State College Boulevard, Imperial Highway, Lambert Road, Birch Street, Puente Street, Berry Street, Brea Boulevard, and Valencia Avenue. Certain roads are classified as restricted truck routes, which prohibit trucks exceeding a maximum gross weight of 6,000 pounds from accessing from 8:00 PM to 6:00 AM. Carbon Canyon Road, east of Valenica Avenue, is restricted to trucks with four axles or fewer.

One of the largest generators of truck activity on streets within Brea is the Olinda Alpha Landfill, located in the northeast of the City. The 565-acre landfill processes nearly 7,000 tons per day, and is a significant generator of commercial and public disposal truck trips.5 Access to the Olinda Alpha Landfill is provided via Valencia Avenue, north of Lambert Road. In addition, the western portion of the City south of Central Avenue and west of Tamarack Avenue, as well as the southeast corner of the City south of Birch Street and east of Kraemer Boulevard have goods movement activities generated by the warehousing, light industrial, and logistic uses.

The Surface Transportation Assistance Act (STAA) of 1982 defines a network of state facilities as truck routes which accommodate large trucks. SR 57, which runs through Brea, is a STAA-designated truck route. In addition, the City of Brea also designates multiple other roads as truck routes. These routes are described in Table 3.

Table 3: Existing Truck Routes
On Road From Road To Road Direction
of Travel
SR 57 Freeway Southern City Boundary Northern City
Boundary
N/S
Brea Boulevard Southern City Boundary Northern City
Boundary
N/S
Puente Street Southern City Boundary Whitter Avenue N/S Berry Street Imperial Highway Central Avenue N/S
Kraemer Boulevard Southern City Boundary Imperial Highway N/S Valencia Avenue Southern City Boundary Northern City
Boundary
N/S
State College Boulevard Brea Boulevard Southern City
Boundary
N/S
Nasa Street/Enterprise Street/Ranger
Street/Voyager Avenue
Valencia Avenue Birch Street N/S/E/W
Imperial Highway Western City Boundary Eastern City Boundary E/W Lambert Road Western City Boundary State College
Boulevard
E/W
Central Avenue Western City Boundary Brea Boulevard E/W Carbon Canyon Road Valencia Avenue Eastern City Boundary E/W Birch Street Voyager Avenue Valencia Avenue E/W
Source: City of Brea, Truck Route Map
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Figure 5: Existing Truck Routes
Section 4 — Regulatory Setting
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REGULATORY SETTING
This section summarizes applicable federal, state, regional, and local plans pertinent to the City of Brea. This information provides a context for the transportation impact discussion related to the project’s consistency with applicable policies, plans, laws, and regulations.

STATE REGULATIONS

CALIFORNIA DEPARTMENT OF TRANSPORTATION
The California Department of Transportation (Caltrans) manages the operation of state highways and is the primary state agency responsible for transportation issues. One of its duties is the construction and maintenance of the state highway system. Caltrans approves the planning, design, and construction of improvements for all state-controlled facilities within the City. Freeway segments, freeway ramps and intersections associated with freeway on- and off-ramps fall under Caltrans jurisdiction.

State highways in the City include State Route (SR) 57, the City’s main north/south limited access thruway, Imperial Highway (SR 90), which runs east/west across the southern section of the City, and SR 142, which runs northwest to San Bernardino County along Valencia Avenue and Carbon Canyon Road.

Caltrans has developed procedures to determine if state-controlled facilities require improvements. For projects that may physically affect facilities under its administration, Caltrans requires encroachment permits before any construction work may be undertaken. For projects that would not physically affect facilities but may influence traffic flow and operational deficiencies at such facilities, Caltrans may recommend measures to address adverse effects from traffic caused by such projects. Caltrans also prepares comprehensive planning documents, including Corridor System Management Plans and Transportation Concept Reports, which are long-range planning documents that establish a planning concept for state facilities.

Caltrans updated its guidance in 2020 to include metrics to evaluate transportation impacts based on vehicle miles traveled (VMT) and no longer sets a minimum acceptable level of service (LOS) for its facilities.

Based on the Caltrans Vehicle Miles Traveled-Focused Transportation Impact Study Guide, Caltrans has transitioned from LOS performance standards to VMT to identify significant impacts. “For land use projects and plans, automobile delay is no longer considered a significant impact on the environment under CEQA (SB 743, 2013). Caltrans review of land use projects and plans is focused on a VMT metric, consistent with changes to the CEQA Guidelines (California Code of Regulations Section 15064.3(b)(1)). This VMT-focused TISG provides a foundation for review of how lead agencies apply the VMT metric to CEQA project analysis.

Beyond or in addition to the use of the VMT metric, determining how the State Highway System may otherwise be affected by a land use project may still be necessary at times, particularly as it relates to the safety of the traveling public. Additional future guidance will include the basis for requesting transportation impact analysis that is not based on VMT. This guidance will include a simplified safety analysis approach that reduces risks to all road users and focuses on multi-modal conflict analysis as well as access management issues. With this guidance the Department will transition away from requesting LOS or other vehicle operations analyses of land use projects.” Note that LOS analyses may be required by Caltrans for local operational assessments (e.g., to support a queueing analysis at ramp terminus intersections).

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ASSEMBLY BILL 32, SENATE BILL 32, AND SENATE BILL 375
Assembly Bill (AB) 32, also known as the Global Warming Solutions Act of 2006, committed California to reducing greenhouse gas (GHG) emissions to 1990 levels by 2020. In 2016, SB 32 added a new target:
reducing statewide emissions to 40 percent below 1990 levels by 2030.

SB 375 provides guidance for curbing emissions from cars and light trucks to help California comply with AB

32. There are five major components to SB 375:
/ Air Resources Board (ARB) will guide the adoption of GHG emission targets to be met by each Metropolitan Planning Organization (MPO) in the state.
/ MPOs are required to create a Sustainable Communities Strategy (SCS) that provides a plan for meeting these regional targets. The SCS must be consistent with the Regional Transportation Plan (RTP). / Regional housing elements and transportation plans must be synchronized on eight-year schedules.

Also, the SCS and Regional Housing Needs Assessment (RHNA) must be consistent with each other. / CEQA is streamlined for preferred development types such as mixed-use projects and transit-oriented developments (TODs) if they meet specific requirements. / MPOs must use transportation and air emission modeling methodologies consistent with California Transportation Commission (CTC) guidelines.

CALIFORNIA COMPLETE STREETS ACT OF 2008 (AB 1358)
Originally passed in 2008, California’s Complete Streets Act took effect in 2011 and requires local jurisdictions to plan for land use transportation policies that reflect a “complete streets” approach to mobility. “Complete streets” comprises a suite of policies and street design guidelines which provide for the needs of all road users, including pedestrians, bicyclists, transit operators and riders, children, the elderly, and the disabled. From 2011 onward, any local jurisdiction—county or city—that undertakes a substantive update of the circulation element of its general plan must consider “complete streets” and incorporate corresponding policies and programs. In 2010, OPR released guidelines for compliance with this legislation which provide direction on how circulation elements can best plan for a variety of travel modes such as transit, walking, bicycling, and freight.

On December 7, 2021, Caltrans announced a new policy for all new transportation projects it funds or oversees to include “complete street” features that provide safe and accessible options for people walking, biking, and taking transit. This policy will expand the availability of sustainable transportation options to help meet the State’s climate, health, and equity goals.

SENATE BILL 743
Senate Bill (SB) 743, which was signed into law on September 27, 2013 and became mandatory on July 2, 2020, fundamentally changed transportation impact analysis as part of California Environmental Quality Act (CEQA). In its Technical Advisory on Evaluating Transportation Impacts in CEQA, the California Governor’s Office of Planning and Research (OPR) provided recommendations for jurisdictions to implement SB 743-compliant transportation analyses. OPR’s recommendations are not binding and lead agencies ultimately have the discretion to set or apply their own significance thresholds, provided they are based on substantial evidence. CEQA Guidelines Section 15064.3 describes how transportation impacts are to be analyzed under SB 743. It states that in general, transportation impacts are best measured by evaluating the project’s vehicle miles traveled. For land use projects, vehicle miles travelled (VMT) exceeding an applicable threshold of significance may indicate a significant impact.

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In October 2020, Brea adopted a resolution that conforms with SB 743, transitioning to a VMT-based method of identifying transportation impacts for CEQA compliance and committing to meet requirements of all future revisions to CEQA, consistent with the guidance provided by the State. The City of Brea Transportation Impact Assessment (TIA) guidelines require a VMT analysis to be conducted for land use projects as deemed necessary by the City and applies to projects that have the potential to increase the baseline VMT for the City of Brea.6
SENATE BILL 99, ASSEMBLY BILL 101
The California Active Transportation Program (ATP), established by Senate Bill 99 and Assembly Bill 101 in 2013, aims to promote active modes of transportation like biking and walking. It combines various federal and state transportation programs such as the Transportation Alternatives Program, Bicycle Transportation Account, and State Safe Routes to School into one cohesive initiative. The goal is to elevate California as a frontrunner in active transportation efforts.

REGIONAL REGULATIONS

SOUTHERN CALIFORNIA ASSOCIATION OF GOVERNMENTS (SCAG)
Founded in 1965, the Southern California Association of Governments (SCAG) is a Joint Powers Authority comprising local governments and agencies addressing regional issues. Designated both as a Metropolitan Planning Organization (MPO) under federal law and as a Regional Transportation Planning Agency and a Council of Governments under state law, SCAG covers six counties and 191 cities over 38,000 square miles.

SCAG develops long-range regional transportation plans, housing allocations, and contributes to air quality management plans.

On April 4, 2024, SCAG’s Regional Council adopted Connect SoCal (2024 – 2050 Regional Transportation Plan/Sustainable Communities Strategy) for federal transportation conformity purposes only. Connect SoCal outlines more than $750 billion in transportation system investments through 2050.

SCAG created the SoCal Transportation Safety Resource Hub to assist local jurisdictions in advancing transportation safety and meeting annual safety targets. It serves as a centralized source for SCAG's safety programs, data, reports, and resources. The hub includes:
/ Regional transportation safety goals and targets summary / Overview of SCAG's existing transportation safety conditions / Interactive map of SCAG's Regional High Injury Network (HIN) with downloadable data / Resources for local jurisdictions to develop their own HIN / Opportunities to engage in SCAG's ongoing safety efforts / Access to data, tools, funding, and resources from SCAG and other organizations. 6 City of Brea, “Traffic Impact Analysis Guidelines – for Vehicle Miles Travelled and Level of Service Assessment”, 2020.

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ORANGE COUNTY TRANSPORTATION AUTHORITY
The Orange County Transportation Authority (OCTA) coordinates transportation planning efforts throughout Orange County and programs funding for project implementation. OCTA leads the following ongoing planning efforts:
/ OCTA oversees Measure M2, the countywide sales tax measure to fund transportation improvements.

Also known as OC GO, this program includes freeway, streets and roads, transit, and environmental projects to help relieve congestion, improve street conditions, expand transit services, synchronize traffic signals, reduce transportation costs for seniors and people with disabilities, and reduce transportation-related air and water pollution.
/ OCTA prepares the Congestion Management Program (CMP), which identifies strategies to address congestion on the County’s CMP network; which includes State highways and principal arterials. CMP Guidelines require analysis of the CMP network in order to measure congestion and to determine how local governments meet CMP standards and requirements. There are four CMP intersections in the City:
o State Route (SR) 57 northbound ramps / Imperial Highway (SR 90) o SR 57 southbound ramps / Imperial Highway
o State College Boulevard / Imperial Highway
o Valencia Avenue / Imperial Highway
/ OCTA administers the Master Plan of Arterial Highways (MPAH), which was established in 1956 to ensure that the County’s regional arterial highway network would be planned, developed, and preserved in order to supplement the freeway system. The MPAH defines the intended functions and carrying capacities of regional roads in the County. In order to be eligible for Measure M2 (also known as OC Go) funding, a city’s General Plan Circulation Element must be consistent with the MPAH; specifically, local Circulation Elements must maintain an equivalent number of minimum through lanes on each arterial highway that is included as part of the MPAH.
/ OCTA’s Long Range Transportation Plan (LRTP) is a long-range policy document that assesses the County’s long-term transportation system and identifies regional projects in the County, which address future population, housing, and employment needs. The LRTP also serves as the County’s local input to SCAG’s broader RTP/SCS for Southern California. OCTA also plans, manages, and operates local transit service within Orange County.

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LOCAL REGULATIONS AND PLANS
All roadways within the City are under the jurisdiction of the City, with the exception of Imperial Highway (SR 90), SR 57, and Carbon Canyon Road / Valencia Avenue (SR 142) which are under Caltrans’ jurisdiction.7
2003 BREA GENERAL PLAN
The Brea General Plan, adopted in 2003, articulates the collective vision of the community for its future and establishes a foundational framework for guiding decisions on development, resource management, public safety, public services, and community well-being. Crafted through collaboration among residents, businesses, educators, and officials, the plan reflects the values and aspirations of Brea. The General Plan Annual Progress Report offers a yearly update on the implementation of its elements, covering activities from January to December. It highlights ongoing projects and programs aimed at enhancing Brea's appeal as a desirable place to live, work, and enjoy leisure activities. The General Plan emphasizes preserving the City's unique natural and aesthetic attributes while adapting to regional growth and evolving community needs. It serves as a policy compass, aligning actions with Brea's overarching vision of making Brea a great place to live, work, learn, and play while respecting natural resources, fostering economic vitality, and enhancing quality of life.

The existing City of Brea General Plan identifies the following goals and visions related to mobility.8 / To improve access to transportation, including accessible public transportation to Northwest neighborhoods;
/ To Improve transportation, pedestrian, and visual connections between Downtown and the rest of the community;
/ To provide for an extensive, integrated, and safe bicycle, hiking, and pedestrian network throughout the community, and to make Brea a pedestrian-friendly community; / To ensure convenient alternative transportation modes allow for an integrated approach to addressing traffic problems;
/ To maintain an effective regional transportation network; / To provide a safe and efficient circulation system that meets the needs of the community; and / To promote the use of alternative transportation modes such as transit, bicycling, and walking.

The current Brea General Plan makes reference to a Growth Management Element, which requires traffic LOS standards. The general target standard is LOS D for intersections and recognizes that lower LOS standards for certain intersections in urbanized areas may be appropriate if such affected roadways carry a high proportion of regional traffic.
7 City of Brea, “Traffic”, accessed May 2024, https://www.ci.brea.ca.us/1139/Traffic 8 City of Brea, “General Plan”, 2003 City of Brea Focused General Plan Update And Brea Code Specific Plan: Transportation Impact Analysis April 2026 Regulatory Setting
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CITY OF BREA CONNECTING THE CORE|ACTIVE TRANSPORTATION
PLAN (2017)
The Brea Connecting the Core Active Transportation Plan (ATP) was developed as phase one of the Brea Core Specific Plan effort, to study cyclist and pedestrian safety along major corridors and to explore ways to improve the safety and experience for cyclists and pedestrians within Brea’s Core Area. The plan identified mobility challenges and proposed solutions to encourage walking and biking, emphasizing access for all, safety enhancements, and creative design solutions. The plan was funded through a grant from Caltrans and was completed in 2020. The Brea Connecting the Core Active Transportation Plan will allow staff to pursue grant funding for pedestrian and bicycle improvements in the Brea Core Area.

The plan will also serve as a component to help update the General Plan and the Brea Core Specific Plan with respect to circulation, urban design, and bikeways. Major components of the ATP include:
/ Three core elements with goals and policies for each:
 Provide access for all users
 Focus on safety enhancements
 Institute creative design solutions
/ A toolbox of improvements outlining facility types to improve multimodal transportation infrastructure. / A detailed set of improvement options for ten (10) corridors in the Brea Core Area included opportunities and recommendations for potential improvements. / Steps to implement the ATP including pursuit of funding, regional coordination, environmental review, community outreach, and improvement designs.9
The preparation of the new Specific Plan for the Brea Core Area will help to implement the City’s long-term vision for this unique area of the City by providing specific direction for development. The Brea Core Specific Plan will incorporate recommendations from the Connecting the Core ATP in order to improve the safety and experience of cyclist and pedestrians in the area, and will build upon findings in the ATP report to address improvements to streets, sidewalks, and public spaces. The plan will evaluate and establish land use designation, zoning regulations, and design guidelines for future change to existing uses and new development. The plan provides an opportunity to continue the Brea Envisions conversation and dig deeper into the community’s values and vision for the heart of the City.

BREA CAPITAL IMPROVEMENT PROGRAM (CIP)
Brea’s Public Works Department plans, designs, and implements capital projects to improve and preserve community assets. The goals of the CIP are to enhance the community's quality of life, ensure a safe environment, and improve transportation, utilities, and City facilities. The CIP budget plan is both a planning and implementation document. The current seven-year CIP includes the appropriation of funds for Fiscal Year (FY) 2025-26 and FY 2026-27 with a planning horizon through 2032. The remaining five years of the CIP are not a commitment of funds but used as a long-range planning tool for subsequent investments in the City's infrastructure. There are currently 72 projects in the current 7-year CIP budget plan estimated at nearly $112 million. The CIP categories include Street Improvements, Storm Drain Improvements, Traffic Safety Enhancements, Water Improvements, Sewer Improvements, Facility Improvements, and Golf Course Improvements. Programmed transportation-related improvements include roadway rehabilitation; interchange, street and intersection improvements; traffic signal equipment upgrades; traffic signal synchronization; traffic calming improvements; and sidewalk replacement and installation. 9 City of Brea, “Brea Connecting the Core Active Transportation Plan”, January 2020.

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CITY OF BREA TRANSPORTATION IMPACT ANALYSIS GUIDELINES (2020) State and federal laws require the correlation between General Plan Land Use Element building intensities and the Circulation Element transportation network capacities. The City of Brea established Transportation Impact Analysis (TIA) Guidelines to outline the specific steps for complying with the new CEQA expectations for VMT analysis and the applicable general plan consistency requirements. A TIA is required by the City of Brea so that the impact of proposed land use modifications and development on the existing and future circulation system can be adequately assessed, and to ensure that the CEQA and relevant CMP laws and guidelines are met.10 The City's TIA Guidelines require LOS analysis outside of CEQA to determine if a new development project would result in congestion and be inconsistent with the LOS goals in the General Plan.

As part of the North Orange County Collaborative, Brea released the North Orange County Collaborative (NOCC+) Traffic Study Screening Tool in 2020.11 The tool assessed a project’s need for further VMT analysis based on three screenings for Transit Priority Areas (TPA), Low VMT Areas, and Project Types. The City has designated the Brea Mall Transit Center as a TPA. Low VMT Areas are defined as Traffic Analysis Zones [TAZs] lower than 15% of the citywide average. As of 2020, the City of Brea General Plan buildout VMT was calculated to be 29.9 VMT per service population.12
It should be noted that CEQA requirements change as the CEQA Guidelines are periodically updated and/or legal opinions are rendered that change how analysis is completed. As such, the City of Brea will continually review their guidelines for applicability, and consultants should contact the City to ensure that they are applying the most recent guidelines for project impact assessment.13 10 California Governor’s Office of Planning Research, “Technical Advisory on Evaluating Transportation Impacts in CEQA”, December 2018. 11 City of Brea, “Transportation Impact Analysis (TIA) Guidelines”, September 2020; NOCC+ is based on data from 2020 and utilizes OCTAM version 5. As such, it may require updates to align with current best practices, the latest version of OCTAM, and subsequent legal rulings. 12 Ibid.
13 Ibid.

Section 5 — Transportation Impact Analysis
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TRANSPORTATION IMPACT ANALYSIS
This transportation impact analysis assesses Brea’s transportation system relative to the State’s CEQA guidelines.

ANALYSIS SCENARIOS, METHODOLOGIES, AND

MODELING APPROACH
This section summarizes the approach to the transportation analyses, including VMT, based on discussions with City staff and consistent with the City of Brea Transportation Impact Analysis Guidelines.14

ANALYSIS SCENARIOS
As part of this study, the following scenarios were developed and analyzed:
 Baseline Conditions – This scenario represents existing conditions at the time of the Notice of Preparation.
 Baseline Plus Project Conditions – This scenario represents the updated General Plan’s land uses being added to the City’s TAZs.
 General Plan No Buildout (2050) – This scenario represents the land uses, densities, and circulation network in the City with the current General Plan.
 General Plan Buildout (2050) Conditions – This scenario represents the buildout land uses, densities, and circulation network changes in the City as defined by the proposed General Plan Update.

The General Plan Buildout (2050) condition incorporates citywide buildout estimates that represent a hypothetical scenario of development in the City required for CEQA. Based on historical development patterns in Brea, it is likelier that development would occur at levels lower than the buildout estimate, due to factors such as standards governing density and floor area ratio, and physical factors such as topography.

ANALYSIS METHODOLOGIES
The appropriate metrics, methodologies, and standards for the analysis were developed based on the City’s guidelines and in consultation with City staff.

CEQA VMT Analysis
Senate Bill 743 (SB 743) was signed into law in September 2013. It required changes to the CEQA Guidelines regarding the analysis of transportation impacts. Historically, CEQA transportation analyses of individual projects determined impacts in the circulation system in terms of roadway delay and/or capacity at specific locations. SB 743 changes included the elimination of auto delay, level of service (LOS), and other similar measures of vehicular capacity or traffic congestion as a basis for determining significant impacts and identified vehicle miles traveled (VMT) as the most appropriate metric to evaluate a project’s significant transportation impacts. Since the bill has gone into effect (July 1, 2020), automobile delay, as measured by “level of service” and other similar metrics, no longer constitute a significant environmental effect under CEQA.

In September 2020, the City of Brea prepared its Transportation Impact Analysis (TIA) Guidelines. These serve as the City’s transportation analysis guidelines and include methodologies and criteria for evaluating VMT 14 City of Brea, “Transportation Impact Analysis (TIA) Guidelines”, 2020 City of Brea Focused General Plan Update And Brea Core Specific Plan: Transportation and Vehicles Miles Traveled (VMT) Impact Analysis
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impacts. The City requires the analysis of citywide VMT per service population (residents + employees) to determine VMT impacts.

The specific thresholds to determine potential VMT impacts are detailed below:
 A project would result in a significant project-generated VMT impact if either of the following conditions are satisfied:
o The baseline or cumulative project-generated VMT per service population exceeds the City of Brea General Plan Buildout VMT per service population, or  The project’s effect on VMT would be considered significant if it resulted in either of the following conditions to be satisfied:
o The baseline or cumulative link-level boundary Citywide VMT per service population increases under the plus project condition compared to the no project condition.

MODELING APPROACH
The Orange County Traffic Analysis Model (OCTAM) is used to forecast VMT metrics for cities in Orange County. OCTAM is a conventional travel demand forecasting model that is similar in structure to most other current models used for traffic forecasting. It uses land use, socioeconomic, and network data to estimate travel patterns, roadway traffic volumes, and performance measures.

The travel demand model land use inputs (socioeconomic data) are aggregated at the transportation analysis zone (TAZ) level. A TAZ is a geographic area used in the model which contains the trip-generating inputs for that area. Population-related inputs include numbers of households by type, which are further stratified by six combinations of unit types and vehicle ownership. Non-residential inputs include building area for 14 employment categories, numbers of students for three types of schools, and acres of recreation (these categories are simplified for the buffer areas outside the Brea City limits).

Travel demand to and from areas outside of the model area are not estimated based on specific land uses, but are instead represented by base year (2024) and projected (2050) traffic volumes on the gateway roads at the model area boundary.

To account for the change in permitted land uses between the current 2003 General Plan and this proposed Focused General Plan Update, the total population and employment were determined for each TAZ that is within the city limits and provided to OCTA for coding into OCTAM. From the model, OCTA provided VMT statistics for the city’s TAZs.

SIGNIFICANT IMPACT THRESHOLDS

VMT IMPACTS
For the purposes of this transportation impact analysis, at least one of the following criteria must be met to determine that there is a significant VMT impact, per the City of Brea Transportation Impact Analysis Guidelines:
 The baseline OR cumulative project-generated VMT per service population exceeds the City of Brea General Plan Buildout VMT per service population.
 The baseline OR cumulative link-level boundary Citywide VMT per service population increases under the plus project condition compared to the no project condition.

This impact analysis is based on citywide total VMT per service population (residents + employees).

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OTHER TRANSPORTATION IMPACTS
In addition to VMT, additional transportation-related impact criteria are as follows:
 The project conflicts with a program, plan, ordinance, or policy addressing the circulation system, including transit, roadway, bicycle, and pedestrian facilities.  The project substantially increases hazards due to a geometric design feature (e.g., sharp curves or dangerous intersections) or incompatible uses (e.g., farm equipment).  The project results in inadequate emergency access.

ITEM 1: VMT

EXISTING VEHICLE MILES TRAVELED
The existing VMT was estimated based on outputs generated by OCTAM for current Brea conditions.

Consistent with the City’s guidelines, two types of VMT were determined15:
 Total VMT: This calculation represents the total daily VMT that starts and/or ends within a boundary (such as the City of Brea) but does not include VMT that travels through an area without starting or stopping there. VMT starting or ending within the City is not truncated at City boundaries.  VMT per Service Population: This calculation represents the VMT for all trips that originate or end within an area, divided by that area’s service population (residents + employees). VMT starting or ending within the City is not truncated at City boundaries.

At the city level, existing total daily VMT is 1,168,996 and existing VMT per service population is 31.6.16 2050 GENERAL PLAN BUILDOUT VEHICLE MILES TRAVELED
For the purpose of this analysis, the horizon year is considered 2050, and the project is defined as the buildout of the proposed General Plan Update.

VMT per service population (SP) represents all trips that originate or end within the area, divided by the city’s service population (residents + employees). The technical data received from OCTA determining the VMT per SP is included in the Appendix.

The City of Brea General Plan Buildout VMT per service population (i.e., with the current General Plan) is

31.1. Table 4 shows the VMT per SP in the baseline project-generated and cumulative project-generated scenario and compares to the current Buildout amounts. As shown, the VMT per service populations in both the Baseline plus Project and Cumulative plus Project scenarios do not exceed the City of Brea General Plan Buildout VMT per service population. Therefore, there would not be a significant VMT impact for this threshold.

Table 4: Citywide VMT per Service Population Analysis
Scenario VMT per SP1 Exceeds Brea Buildout VMT
per SP (31.1)?
Baseline Plus Project 29.8 No
Cumulative Plus Project 30.0 No 1 VMT per SP is determined from dividing the OD VMT by the sum of the population and employment in the Baseline Project-Generated model run scenario and the Cumulative Project-Generated model run scenario. 15 City of Brea, “Transportation Impact Analysis (TIA) Guidelines”, 2020 16 Note the base year received and analyzed from OCTA was 2019.

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Link-level boundary citywide VMT per SP represents the total daily VMT that starts and/or ends within the City but does not include VMT that travels through the area without starting or stopping there, divided by the area’s service population (residents + employees). The technical data determining the link-level boundary citywide VMT per SP is included in the Appendix.

Table 5 shows the link-level boundary citywide VMT per service population in the baseline plus project and cumulative plus project scenarios. As shown, the VMT per service populations in both scenarios do not exceed the link-level VMT per service population in the respective no-project scenarios. Therefore, there would not be significant VMT impact for this threshold.

Table 5: Link-Level Boundary Citywide VMT per Service Population Threshold Scenario No Project
(VMT per SP)
Plus Project
(VMT per SP)
Plus-Project VMT/SP
Exceeds Respective NoProject VMT/SP?
Baseline 12.7 11.0 No
Cumulative 12.3 11.2 No
Overall, the General Plan Update’s VMT impacts would be considered less than significant.

Brea Core Specific Plan Area
As the Brea Core Specific Plan Area is a subset of the overall General Plan, a separate Core Area VMT analysis is not required. However, for informational purposes, the Core Area’s VMT per SP, based on the overall citywide VMT, was determined.

To estimate Core Area’s VMT, the proportion of the VMT that was attributable to the Core Area was identified. Using OCTAM data, the model Traffic Analysis Zones (TAZs) that were partially or completely within the Core Area, and the proportion of land uses within each TAZ, were identified. From this data, the percentage of the citywide ADT that would be generated by trips to, from, and within in the Core Area for the Cumulative No Build (i.e., with the current General Plan) and Future 2050 Plus Project scenarios were estimated. For the VMT analysis, the total VMT for each TAZ was determined and the VMT per service population was calculated based on the net change in population and employment for the portion of the TAZ within the Core Area. This data was used to determine the total VMT and VMT per service population as shown in Table 6. The technical analysis is included in the Appendix. As shown in the table, the VMT per SP would decrease with the Project.

Table 6: VMT per Service Population Threshold for the Brea Core Specific Plan Scenario VMT Service Population VMT Per Service
Population
Cumulative No Project
(Current Plan) 728,870 20,292 35.9
Cumulative Plus Project 900,121 28,654 31.4
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ITEM 2: TRANSIT, ROADWAY, BICYCLE, AND

PEDESTRIAN FACILITIES
A significant project impact would occur if the project conflicts with a program, plan, ordinance, or policy addressing the circulation system, including transit, roadway, bicycle, and pedestrian facilities. Each of these modes and facilities is reviewed for impacts below.

ROADWAYS
As land use projects throughout the City are approved and developed, the City will continue to monitor conditions at vehicular facilities to determine the appropriate timing and/or level of improvement along those facilities. In addition, the City can request project-specific circulation analyses once specific land use development projects are undergoing their review and approval processes.

The updated Mobility Element of Brea’s General Plan incorporates policies that guide roadway operations, safety, design, and goods movement. Key supporting policies include:
 M-1.2 Inter-Agency Coordination. Engage in federal, State, and regional planning efforts with Federal Highway Administration (FHWA), the Southern California Association of Governments (SCAG), Orange County Transportation Authority (OCTA), Orange County, adjacent cities, and other jurisdictions, as appropriate, to develop a transportation network that balances traffic flow and multi-modal needs.
 M-1.4 Emerging Technology. Work with regional partners to plan for emerging transportation modes and technologies.
 M-2.1 Roadway Requirements. Require roadways to:
o Be designed to be consistent with applicable federal, State, and local design and safety standards.
o Meet the needs of multiple transportation modes and users, including children, seniors, and people with disabilities.
o Be compatible with the streetscape and surrounding land uses. o Be maintained in accordance with best practices.
 M-2.2 Level of Service. Strive to maintain acceptable vehicular level of service at City intersections, per the City of Brea Transportation Impact Analysis (TIA) Guidelines.  M-2.3 Non-Local Traffic. Discourage the flow of non-local traffic through neighborhoods.  M-2.4. Traffic Management. Apply creative traffic management strategies to maintain efficient and orderly traffic flow, minimize vehicular congestion in areas with unique users (such as schools, and businesses with drive-through access) and other special situations.  M-2.8. Truck Route Network. Maintain, and update as needed, a designated local truck route network that facilitates access to business and shopping centers while reducing commercial vehicle effects on the community.
 M-3.1 Complete Streets Principles. Consider and implement best complete streets practices to facilitate travel and enhance safety for all road users regardless of travel mode.  M-3.5 New Mobility Technologies. Monitor and evaluate the development of new mobility technologies and the considerations for implementation of improvements to facilitate a transportation network that accommodates all modes and users.  M-3.7 Roadway Design Principles. Support roadway design principles that create a safe, pleasant, and comfortable experience for all road users including pedestrians and bicyclists.

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The General Plan Update would not be inconsistent with or in conflict with any adopted program, plan, ordinance, or policy addressing roadway operations, design, or performance. The Mobility Element establishes a policy framework that is consistent with applicable federal, state, and local roadway design and safety standards, including the City of Brea Transportation Impact Analysis (TIA) Guidelines, and provides direction to maintain acceptable roadway operations while accommodating multiple transportation modes. The General Plan Update outlines policies to guide future improvements and requires that roadway conditions be evaluated through project-specific circulation analyses at the time of development. Through continued monitoring of roadway conditions, inter-agency coordination, and implementation of traffic management strategies, the City would ensure that future development occurs in a manner consistent with adopted roadway plans and standards and would not result in conflicts with the circulation system.

TRANSIT, BICYCLE, AND PEDESTRIAN
In addition to proposed roadway classifications, the updated Mobility Element references and incorporates the City’s bicycle and pedestrian plans, which direct efforts to improve non-motorized accessibility and connectivity throughout the City.

The General Plan Update also proposes development within existing and future high-quality transit areas, which can encourage less driving and more transit, bike-to-transit, and walk-to-transit trips.

The Mobility Element developed as part of the General Plan Update contains policies that support access to and the performance of public transit, bicycle, and pedestrian facilities. These policies include:
 M-3.1 Complete Streets Principles. Consider and implement best complete streets practices to facilitate travel and enhance safety for all road users regardless of travel mode.  M-3.6 Curb Management. Seek to implement curb zone changes to best match the needs of adjacent land uses and to facilitate non-motorized transportation choices while minimizing the effects to roadway conditions and on-street parking.
 M-3.7 Roadway Design Principles. Support roadway design principles that create a safe, pleasant, and comfortable experience for all road users including pedestrians and bicyclists.  M-3.8 Traffic Calming. Use traffic calming methods within residential areas as needed to create a pedestrian-friendly circulation system, while accommodating local street patterns where feasible.

Balance accommodations for automobiles, transit, bicycles, and pedestrians in the design of new streets and streetscape improvements.
 M-3.9 New Development – Multi-Modal Facilities. Require new development projects to accommodate vehicles (including emergency vehicles), pedestrians, and bicycles through the dedication of land for public improvements such as roadways, wider sidewalks, and/or bicycle lanes, as appropriate and warranted by the project.
 M-4.1 System of Bikeways. Develop and maintain a comprehensive and integrated system of bikeways that promotes cycling for commuting and recreation.  M-4.3 Pedestrian Connections. Provide for safe and convenient pedestrian connections to and from Downtown, other commercial districts, neighborhoods, and major activity centers within the City.
 M-4.7 Bicycle, Pedestrian, and Connectivity Improvements. Provide safe, attractive, and accessible bicycle and pedestrian facilities—such as secure bicycle parking, pedestrian-scale lighting, and landscaping—and to make improvements that enhance connectivity to key destinations like schools, parks, workplaces, and shopping areas that serve residents’ daily needs where feasible.
 M-4.10 Bicycle and Pedestrian Connectivity. Plan neighborhood streets, pedestrian walks, and bicycle paths as a system of fully connected routes throughout the City.

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The General Plan Update would not be inconsistent with or in conflict with any adopted program, plan, ordinance, or policy addressing the circulation system. The Mobility Element is an updated policy framework that incorporates and builds upon the City’s existing transit, bicycle, and pedestrian goals and objectives. Policies in the Mobility Element promote multimodal access, connectivity, safety, and transitsupportive land use patterns, and do not propose actions that would degrade or preclude implementation of planned roadway, transit, bicycle, or pedestrian facilities. Development in high-quality transit areas and the requirement for multimodal accommodations in new development are consistent with State and local complete streets and sustainable transportation policies, and would not conflict with adopted circulation standards or performance objectives.

Therefore, the General Plan Update’s impacts related to roadways, transit, bicycle, and pedestrian facilities would be considered less than significant.

ITEM 3: GEOMETRIC DESIGN AND INCOMPATIBLE

USE HAZARDS
A significant project impact would occur if the project substantially increases hazards due to a geometric design feature (e.g., sharp curves or dangerous intersections) or incompatible uses (e.g., farm equipment).

Note, the General Plan Update is a programmatic level document; increased hazards due to geometric design features are typically assessed at the project level. As individual sites are developed and undergo City review and approval, the City can require site plan, access, and circulation analysis to ensure that neither on-site designs nor the interaction with City streets will result in hazardous geometric design features.

The types of uses included within the City of Brea as part of the General Plan Update are generally similar to existing and surrounding uses and thereby are compatible with the existing uses in the Plan area and in the surrounding area.

In addition, the Mobility Element developed as part of the General Plan Update contains policies in support of roadway network safety and reducing design hazards, including:
 M-1.4 Emerging Technology. Work with regional partners to plan for emerging transportation modes and technologies.
 M-2.1 Roadway Requirements. Require roadways to:
o Be designed to be consistent with applicable federal, State, and local design and safety standards.
o Meet the needs of multiple transportation modes and users, including children, seniors, and people with disabilities.
o Be compatible with the streetscape and surrounding land uses. o Be maintained in accordance with best practices.
 M-2.8 Truck Route Network. Maintain, and update as needed, a designated local truck route network that facilitates access to business and shopping centers while reducing commercial vehicle effects on the community.
 M-3.1 Complete Streets Principles. Consider and implement best complete streets practices to facilitate travel and enhance safety for all road users regardless of travel mode.  M-3.5 New Mobility Technologies. Monitor and evaluate the development of new mobility technologies and the considerations for implementation of improvements to facilitate a transportation network that accommodates all modes and users.  M-3.9 New Development – Multi-Modal Facilities. Require new development projects to accommodate vehicles (including emergency vehicles), pedestrians, and bicycles through the dedication of land for public improvements such as roadways, wider sidewalks, and/or bicycle lanes, as appropriate and warranted by the project.

Therefore, the General Plan Update’s impacts related to geometric design and incompatible use hazards would be considered less than significant.

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ITEM 4: EMERGENCY ACCESS
A significant project impact would occur if the results in inadequate emergency access. Note that the General Plan Update is a programmatic level document; emergency accessibility is typically assessed at the project level. As individual sites are developed and undergo City review and approval, the City can require site plan, access, and circulation analysis to ensure that neither on-site designs nor the interaction with City streets will result in inadequate emergency access.

In Brea, emergency access and public safety are addressed through the General Plan, including within the Mobility Element. The Mobility Element provides a framework to ensure that development and transportation planning support adequate emergency response capabilities.

The Mobility Element supports emergency access through roadway design, traffic management, and multimodal system planning that ensures access for emergency vehicles and clear evacuation paths. The Element emphasizes maintaining a connected and resilient street network that accommodates all users, including emergency responders, even in high-density or transit-oriented areas.

Relevant supporting policies include:
 M-1.2 Inter-Agency Coordination. Engage in federal, State, and regional planning efforts with Federal Highway Administration (FHWA), the Southern California Association of Governments (SCAG), Orange County Transportation Authority (OCTA), Orange County, adjacent cities, and other jurisdictions, as appropriate, to develop a transportation network that balances traffic flow and multi-modal needs.
 M-2.7 Evacuation Routes. Incorporate necessary improvements to and perform maintenance on evacuation routes consistent with the Public Safety Element, and according to applicable requirements identified in regional and local plans.
 M-3.9 New Development – Multi-Modal Facilities. Require new development projects to accommodate vehicles (including emergency vehicles), pedestrians, and bicycles through the dedication of land for public improvements such as roadways, wider sidewalks, and/or bicycle lanes, as appropriate and warranted by the project.

In addition, the Mobility Element is supported by the General Plan’s Public Safety Element, which outlines strategies to mitigate risks associated with natural hazards, including wildfires, floods, and earthquakes.

Key Safety Element policies and programs include:
 PS-1.19 Mutual Aid. Maintain mutual aid agreements with the State, County, and neighboring jurisdictions including for disaster response and evacuation assistance.  PS-1.20 Public Information. Continue annual public information programs that explain the City’s Emergency Preparedness Program and other emergency preparedness strategies, including defensible space and evacuative routes, focusing on the most vulnerable communities such as those in the Very High Fire Hazard Severity Zones.
 PS-3.4 Education. Educate the community regarding flood prevention information and notify residents and motorists of impending flood hazards and evacuation procedures.  PS-4.3 Transport. Limit the transport of hazardous waste and materials to designated routes.  PS-6.5 Automatic and Mutual Aid. Continue to participate in automatic and mutual aid agreements with adjacent service providers to ensure efficient and adequate resources, facilities, and support services during and after emergencies.
 PS-6.6 Emergency Evacuation Routes and Access. Work with the Fire Department and Police Department to define minimum standards for evacuation of residential areas, particularly in HFHSZs and VHFHSZs, and to maintain, update, and regularly exercise emergency access, protocols, and evacuation routes to assess their effectiveness under a range of emergency scenarios. If areas with inadequate evacuation routes are identified, develop appropriate mitigation measures, improvement plans, or education programs to ensure safe evacuation.

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 PS-6.8 Collaboration. Strengthen emergency services preparedness and response by linking emergency services with local hazard mitigation programs and enhancing public education on a regional scale.
 PS-6.9 Institutions. Regularly coordinate with the City’s major institutions, schools, employers, and homeowners’ associations regarding emergency response procedures.  PS-6.11 Warning Systems. Maintain and regularly upgrade a mass communications system to effectively notify people during disasters and emergencies by using current communication technologies.
 PS-6.12 Strategic Readiness. Maintain a proactive, data-driven public safety system through recurring five-year strategic planning that aligns resources, facilities, staffing, and technology with community risk and growth.

The General Plan Update would not be inconsistent with or in conflict with any adopted program, plan, ordinance, or policy addressing emergency access and response. The Mobility Element and Public Safety Element collectively establish policies that ensure roadway design, circulation planning, and development review processes maintain adequate access for emergency vehicles and evacuation needs. These policies are consistent with applicable local and regional requirements, including roadway standards, evacuation route planning, and fire safety regulations codified in the Brea Municipal Code. The General Plan Update does not propose physical changes that would obstruct emergency access, and emergency access adequacy is evaluated and enforced through subsequent project-level review. Implementation of the General Plan Update would not result in inadequate emergency access or conflict with adopted emergency response and circulation policies.

Therefore, the General Plan Update’s impacts related to emergency access would be considered less than significant.

Section 6 — Conclusions
City of Brea Focused General Plan Update And Brea Core Specific Plan: Transportation and Vehicle Miles Traveled (VMT) Impact Analysis
April 2026 Conclusions

CONCLUSIONS
The California Environmental Quality Act (CEQA) transportation impact analysis of the General Plan Update determined that impacts would be less than significant for the following topics:
 Vehicle miles traveled (VMT)
 Transit, roadway, bicycle, and pedestrian facilities
 Geometric design and incompatible use hazards
 Emergency access
Appendix 1 — VMT
Technical Data
OCTA TAZs WITHIN CITY LIMITS
Baseline Scenario
TAZ Time Period OD VMT POPULATION EMPLOYMENT SERVICE POP 2 Daily 49,502 1,877 110 1,987
3 Daily 80,599 2,235 589 3,422
4 Daily 64,730 2,268 200 2,959
8 Daily 1,163 30 6 36
10 Daily 53,998 2,696 234 2,930
11 Daily 41,677 1,482 479 3,774
12 Daily 52,451 2,019 562 2,581
13 Daily 84,294 16 3,273 3,289
14 Daily 190,310 3,378 3,289 6,667
15 Daily 53,877 82 2,067 2,149
16 Daily 36,101 0 1,055 1,055
17 Daily 24,234 5 1,003 1,008
18 Daily 38,898 347 974 1,321
19 Daily 39,193 17 1,044 1,061
20 Daily 212,347 410 4,064 4,474
21 Daily 29,094 1,119 184 1,944
22 Daily 89,584 3,371 609 4,248
23 Daily 137,090 1,972 2,836 5,731
24 Daily 287,265 3,539 4,655 10,041
25 Daily 146,635 2,046 2,889 4,935
26 Daily 438,075 1,251 7,434 9,135
27 Daily 63,935 1,467 1,015 2,482
29 Daily 61,782 2,208 441 2,649
30 Daily 54,254 2,292 260 3,107
31 Daily 21,202 989 179 1,852
32 Daily 3,537 9 118 127
33 Daily 61,032 574 901 1,475
34 Daily 113,843 1,530 1,029 2,721
35 Daily 261,906 0 6,400 6,400
36 Daily 78,746 2,496 713 3,209
39 Daily 32,230 1,470 164 1,634
TOTALS 2,903,584 43,195 48,776 91,971
VMT 2,903,584
Service Population 91,971
VMT per SP 31.6
Baseline Plus Project Scenario
TAZ Time Period OD VMT POPULATION EMPLOYMENT SERVICE POP 2 Daily 56,299 2,233 0 2,233
3 Daily 85,287 2,666 262 2,928
4 Daily 82,845 2,910 184 3,094
8 Daily 27,123 790 0 790
10 Daily 56,113 2,754 13 2,767
11 Daily 9,328 203 0 203
12 Daily 50,063 2,196 743 2,939
13 Daily 127,118 0 6,994 6,994
14 Daily 190,672 3,210 5,523 8,733
15 Daily 46,280 0 2,273 2,273
16 Daily 66,289 0 3,724 3,724
17 Daily 72,280 0 3,843 3,843
18 Daily 56,620 546 2,243 2,789
19 Daily 33,832 0 1,684 1,684
20 Daily 169,706 1,786 1,849 3,635
21 Daily 41,960 1,230 315 1,545
22 Daily 79,230 2,349 595 2,944
23 Daily 177,395 1,739 4,795 6,534
24 Daily 177,477 3,787 1,357 5,144
25 Daily 141,519 3,989 1,716 5,705
26 Daily 260,936 4,840 3,331 8,171
27 Daily 89,131 2,107 887 2,994
29 Daily 69,006 2,488 434 2,922
30 Daily 42,228 1,825 109 1,934
31 Daily 28,935 1,824 168 1,992
32 Daily 141,634 2,030 1,309 3,339
33 Daily 90,404 1,172 746 1,918
34 Daily 46,786 2,287 3 2,290
35 Daily 768,632 2,174 14,300 16,474
36 Daily 273,169 2,911 3,973 6,884
39 Daily 12,058 465 51 516
TOTALS 3,570,351 56,511 63,424 119,935
VMT 3,570,351
Service
Population 119,935
VMT per SP 29.8
2050 General Plan No Buildout (City of Brea with the current General Plan VMT) TAZ Time Period OD VMT POPULATION EMPLOYMENT SERVICE POP 2 Daily 53,747 1,798 113 1,911
3 Daily 87,032 2,113 695 2,808
4 Daily 68,792 2,241 222 2,463
8 Daily 1,254 28 7 35
10 Daily 57,391 2,513 233 2,746
11 Daily 42,066 1,433 527 1,960
12 Daily 52,393 1,841 620 2,461
13 Daily 92,024 16 3,690 3,706
14 Daily 203,152 3,733 3,488 7,221
15 Daily 84,762 516 2,878 3,394
16 Daily 36,445 0 1,158 1,158
17 Daily 26,785 5 1,199 1,204
18 Daily 41,393 532 1,035 1,567
19 Daily 43,228 17 1,291 1,308
20 Daily 216,425 432 4,320 4,752
21 Daily 31,282 1,096 196 1,292
22 Daily 92,835 3,340 623 3,963
23 Daily 150,641 1,797 3,228 5,025
24 Daily 284,833 3,560 4,480 8,040
25 Daily 144,934 2,958 2,628 5,586
26 Daily 428,343 1,281 7,635 8,916
27 Daily 66,647 1,541 1,040 2,581
29 Daily 60,607 2,013 432 2,445
30 Daily 55,437 2,089 287 2,376
31 Daily 54,213 2,509 314 2,823
32 Daily 51,250 1,724 55 1,779
33 Daily 69,072 523 1,030 1,553
34 Daily 119,757 1,438 1,096 2,534
35 Daily 259,658 0 7,115 7,115
36 Daily 106,321 3,121 817 3,938
39 Daily 34,082 1,417 164 1,581
TOTALS 3,116,801 47,625 52,616 100,241
VMT 3,116,801
Service Population 100,241
VMT per SP 31.1
2050 General Plan Buildout (City of Brea with the proposed General Plan VMT) TAZ Time Period OD VMT POPULATION EMPLOYMENT SERVICE POP 2 Daily 62,076 2,233 0 2,233
3 Daily 89,031 2,666 262 2,928
4 Daily 86,958 2,910 184 3,094
8 Daily 28,330 790 0 790
10 Daily 62,554 2,754 13 2,767
11 Daily 9,124 203 0 203
12 Daily 51,594 2,196 743 2,939
13 Daily 122,950 0 6,994 6,994
14 Daily 191,390 3,210 5,523 8,733
15 Daily 47,295 0 2,273 2,273
16 Daily 62,909 0 3,724 3,724
17 Daily 70,036 0 3,843 3,843
18 Daily 55,668 546 2,243 2,789
19 Daily 32,687 0 1,684 1,684
20 Daily 171,121 1,786 1,849 3,635
21 Daily 42,664 1,230 315 1,545
22 Daily 80,815 2,349 595 2,944
23 Daily 177,133 1,739 4,795 6,534
24 Daily 182,122 3,787 1,357 5,144
25 Daily 145,152 3,989 1,716 5,705
26 Daily 264,930 4,840 3,331 8,171
27 Daily 90,724 2,107 887 2,994
29 Daily 71,324 2,488 434 2,922
30 Daily 44,460 1,825 109 1,934
31 Daily 32,833 1,824 168 1,992
32 Daily 141,726 2,030 1,309 3,339
33 Daily 91,808 1,172 746 1,918
34 Daily 51,478 2,287 3 2,290
35 Daily 755,388 2,174 14,300 16,474
36 Daily 273,790 2,911 3,973 6,884
39 Daily 12,759 465 51 516
TOTALS 3,602,829 56,511 63,424 119,935
VMT 3,602,829
Service
Population 119,935
VMT per SP 30.0
Link-Level VMT
Scenario Total VMT Population Employment Link-Level VMT/SP Baseline 1,168,966 43,195 48,776 12.7
Baseline ProjectGenerated 1,314,010 56,511 63,424 11.0 Cumulative 1,235,653 47,625 52,616 12.3
Cumulative ProjectGenerated 1,343,583 56,511 63,424 11.2 Brea Core Specific Plan Analysis
Baseline
SP
Factor TAZ OD VMT Specific PlanOD VMT Population Specific Plan Pop Employment Specific PlanEmployment

1.00 18 38,897 38,897 347 347 974 974

0.36 20 212,346 76,179 410 147 4,064 1,457

0.02 22 89,584 1,554 3,371 58 609 10

0.86 23 137,089 117,601 1,972 1,691 2,836 2,432

0.69 25 146,635 101,647 2,046 1,418 2,889 2,002

0.39 26 438,075 172,199 1,251 491 7,434 2,922

0.25 27 63,934 15,918 1,467 365 1,015 252

0.44 33 61,031 26,902 574 253 901 397
Total 550,902 4,772 10,450
VMT / SP 36.2
2050 No-Project
SP
Factor TAZ OD VMT Specific PlanOD VMT Population Specific Plan Pop Employment Specific PlanEmployment

1.00 18 41,392 41,392 532 532 1,035 1,035

0.54 20 216,424 116,275 432 232 4,320 2,320

0.04 22 92,835 3,554 3,340 127 623 23

0.92 23 150,641 139,292 1,797 1,661 3,228 2,984

0.81 25 144,933 117,619 2,958 2,400 2,628 2,132

0.62 26 428,343 265,369 1,281 793 7,635 4,730

0.27 27 6,6647 18,251 1,541 422 1,040 284

0.39 33 69,072 27,113 523 205 1,030 404
Total 728,870 6,375 13,916
VMT / SP 35.9
2050 Project-Generated
SP
Factor TAZ OD VMT
Specific Plan
OD VMT Population
Specific Plan
Pop Employment
Specific Plan
Employment

0.99 18 55,668 55,665 546 545 2,243 2,242

0.99 20 171,121 171,098 1,786 1,785 1,849 1,848

0.06 22 80,815 4,567 2,349 132 595 33

0.76 23 177,132 134,596 1,739 1,321 4,795 3,643

0.99 25 145,151 145,146 3,989 3,988 1,716 1,715

0.99 26 264,930 264,903 4,840 4,839 3,331 3,330

0.57 27 90,724 52,112 2,107 1,210 887 509

0.78 33 91,808 72,031 1,172 919 746 585
Total 900,121 14,744 13,910
VMT / SP 31.4
Specific Plan (SP) Factor represents the proportion of land uses within each TAZ that would be located within the Brea Core Specific Plan Area. This was calculated based on the service population of all parcels within the TAZ, divided by the total service population of the TAZ.

Attachment B. Revised Appendix C: Brea 2050 General Plan: Goals, Policies, and Actions
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Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)

Brea 2050 General Plan: Goals, Policies,
and Actions
This document provides a comprehensive list of the goals, policies, and actions included in the Public Hearing Draft Brea 2050 General Plan. Modifications recommended by the Brea Planning Commission are illustrated in track changes.

Community Development Element
Goal CD-1: Provide a balanced mix of land uses that integrates residential, commercial, and employment uses with open space and public facilities to support a vibrant, sustainable community offering a high quality of life.

CD-1 Policies
● CD-1.1 Land Use Pattern. Provide a coordinated mix of housing, employment, service, and recreational opportunities that encourages efficient development and multimodal choices; minimizes environmental impacts; ensures land use compatibility; enhances community livability and public health; and sustains economic vitality. EJ ● CD-1.2 Housing Options. Support a diverse range of housing development options and densities, ensuring that residents across income levels, age groups, and those with special needs can live within the community. EJ
● CD-1.3 Commercial and Industrial Uses. Provide a balanced distribution of wellmaintained, functional, and appropriate commercial business and industrial use areas to expand local employment opportunities and support a stable tax base. ● CD-1.4 Open Space Areas. Preserve open space wherever possible and to the extent feasible, particularly in hillside areas. EJ
● CD-1.5 Employment/Housing Balance. Strive to balance employment and housing levels within the community to create more opportunities for residents to work locally. A balanced jobs-to-housing ratio enables residents to live and work in Brea, fostering a greater sense of community and convenience. EJ

Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)

● CD-1.6 Economic Growth. Support the preservation, enhancement, and growth of a diverse range of commercial areas, including retail, dining, professional, service, technology, and emerging market sectors to meet the needs of residents and attract new businesses and employment opportunities.
● CD-1.7 Development Flexibility. Allow for flexible development standards in the City’s Zoning Ordinance provided that the potential benefits and merit of projects can be balanced with potential impacts.
● CD-1.8 Sustainable Development Practices. Implement policies and programs that encourage the efficient use of land and infrastructure to reduce environmental impacts and support long-term community sustainability. EJ
● CD-1.9 Connectivity. Connect, where possible, all neighborhoods of the community and surrounding areas located within the City and Sphere of Influence (SOI) with trails, greenways, and well-planned, well-located park areas. Maximize connections to hillside and open space areas. EJ
● CD-1.10 Maintain and Expand Public Facilities. Ensure the planning, maintenance, and enhancement of public facilities and services, including emergency and public safety services, infrastructure, educational and library facilities, and recreational and public gathering areas. These resources support social engagement, cultural activities, and a high quality of life for residents. EJ
● CD-1.11 Multi-Jurisdictional Coordination. Coordinate with neighboring jurisdictions to ensure land use compatibility in areas surrounding Brea. Partnerships with Orange, San Bernardino, and Los Angeles Countiesy and adjacent cities can support the development of cohesive strategies to address regional planning challenges and development. ● CD-1.12 Annexations. Strongly consider the annexation of adjacent unincorporated properties in the City’s Sphere of Influence (SOI) and avoid the creation of any new County islands.
● CD-1.13 Responsible Hillside Development. Regulate development within hillside areas to ensure consistency with City standards and environmental requirements and facilitate orderly development, guide site design to protect natural landforms, preserve natural and biological resources, minimize hazards, and ensure the provision of adequate infrastructure and public services, particularly within service areas and any potential lands proposed for annexation.

Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)

CD-1 Actions
● CD-1a Update the City’s Zoning Map to be consistent with the land use designations shown on Figure CD-2, General Plan Land Use Designations. ● CD-1b Review the standards provided in the Zoning Ordinance (Title 20 of the Brea City Code) and amend as necessary for consistency with General Plan goals, policies, allowed uses, and future growth projections.
● CD-1c File an annual progress report with the City Council and the State of California Office of Planning and Research (OPR) describing the status of the General Plan and its implementation.
● CD-1d Research and explore adaptive reuse strategies for underutilized or aging structures—such as former office buildings, industrial spaces, and retail anchors—to facilitate their conversion into alternative uses.

Goal CD-2: Create a visually appealing and cohesive community that emphasizes highquality design, celebrates Brea’s distinct character, and fosters a strong sense of place through well-designed spaces, architecture, and streetscapes.

CD-2 Policies
● CD-2.1 Distinct Identity. Foster and preserve a distinct community identity and sense of place, characterized by clearly defined districts and neighborhoods. ● CD-2.2 Site Planning and Design. Emphasize high-quality architecture, visual cohesion, and well-planned functional spaces in the design of new developments, while encouraging the optimization of land use for a sustainable, pedestrian-friendly community. ● CD-2.3 Streetscape Design. Provide public space streetscapes that balance aesthetics and functionality, with a focus on the City’s arterial highways, entry gateways, and the Core Area. This includes cohesive design elements such as street furniture, lighting, drought-tolerant landscaping in medians and parkways, and monument signage that enhance Brea’s image and provide a welcoming, visually elevated experience for both residents and visitors. EJ
● CD-2.4 Sustainable Design. Promote environmentally responsive design by integrating natural elements such as drought-tolerant landscaping, efficient irrigation systems, and energy-efficient building materials and design into public and private spaces. EJ ● CD-2.5 Landscape Design. Require visually appealing landscapes that soften and enhance development projects and complement the surrounding environment. Incorporate plant material of varying sizes for layered growth and select species adaptable to the local climate to ensure long-term sustainability. Trees and plants should be native, non-invasive species.

Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)

● CD-2.6 Neighborhood Setting. Ensure new development projects are appropriately scaled and designed with consideration of the surrounding setting. This includes welldesigned building height and massing transitions to complement the surrounding neighborhood’s scale and sharing common aesthetic themes or architectural styles to preserve and enhance the area’s character and sense of place. EJ ● CD-2.7 Public Gathering Spaces. Encourage walkable placemaking projects that feature attractive outdoor gathering spaces conducive to pedestrian-friendly programming (e.g., farmers markets, art shows, live music, food, movie nights) to strengthen social engagement for the community. EJ
● CD-2.8 Pedestrian-Friendly Environments. Prioritize pedestrian-oriented design and connectivity by incorporating thoughtfully planned tree-lined sidewalks, pathways, and active street fronts throughout new developments. This includes a focus on human-scale building frontages that create visually appealing and pedestrian-friendly environments, as well as pedestrian safe connections to surrounding streets. EJ ● CD-2.9 Residential Open Spaces. Ensure that new multifamily residential projects incorporate thoughtfully designed usable open spaces, plazas, park areas, courtyards, and/or other outdoor gathering areas to create inviting environments for social interaction and recreation that make a community a desirable place to live. EJ ● CD-2.10 Façade and Ancillary Improvements. Encourage the revitalization of aging commercial centers and buildings to create more inviting and pedestrian-friendly spaces.

This includes renovating and enhancing building façades, landscaping, signage, and overall property maintenance to build a stronger sense of place and support business attraction and retention.
● CD-2.11 Above-Ground Utilities. Utilities and support structures should be carefully placed and designed to minimize their impact on the streetscape. ● CD-2.12 Historic Preservation. Ensure that new development respects the City’s historic heritage and architecture and is designed to be consistent with the local context and key physical and architectural characteristics of its surrounding neighborhood. ● CD-2.13 Hillsides. Preserve the scenic beauty of Brea’s hillsides and minimize the visual and environmental impact of development upon sensitive hillside areas. ● CD-2.14 Gateways. Reinforce gateways as prominent points of entry into the City of Brea through the use of distinctive public art pieces, signage, and/or graphics that express the history and character of the community.
● CD-2.15 Wildlife-Friendly Design. Support the use of wildlife-friendly design features in new development and public improvements, such as strategies that promote bird safety, Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)

light mitigation, permeability, and ecological landscaping, especially for projects located within or adjacent to the wildland-urban interface to minimize human-wildlife conflicts and protect local biodiversity.

CD-2 Actions
● CD-2a Plan for gateway improvements as funding and potential partnership opportunities become available.
● CD-2b Establish objective design standards (SB 35)
● CD-2c Along arterials, explore strategies and implementation actions to coordinate with private property owners to achieve a consistent appearance of walls and fences facing the corridor.

Goal CD-3: Preserve the safety and tranquility of established residential neighborhoods that contribute to the quality of life in Brea, while fostering opportunities for social interaction and enhancing community connections.

CD-3 Policies
● CD-3.1 Preserve Single-Family Neighborhoods. Focus growth to underutilized parcels within commercial and mixed use areas, thereby reducing development pressure on established single-family residential neighborhoods.
● CD-3.2 New Development Sensitivity. Ensure new development projects are sensitively designed to complement surrounding low-density residential neighborhoods, with particular attention to architectural character, appropriate building massing and scale, and minimizing any operational impacts on the surrounding area. ● CD-3.3 Neighborhood Character. Create a distinctive sense of place and enhance the visual quality of individual neighborhoods.
● CD-3.4 Property Maintenance and Reinvestment. Promote community pride and enhance the City’s visual appeal by encouraging property renovations and reinvestment.

This also includes Brea City Code education and enforcement efforts to ensure proper property maintenance, preserve neighborhood character, and maintain attractive community aesthetics. EJ
● CD-3.5 Neighborhood Infrastructure. Maintain neighborhood infrastructure, community facilities, and services to support the livability and long-term sustainability of neighborhoods. EJ
● CD-3.6 Community Programming. Support local outreach and education initiatives that enhance neighborhoods and strengthen community connections in Brea. EJ Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)

CD-3 Actions
● CD-3a As part of the City’s development review process, ensure that nonresidential development projects are designed to minimize conflicts with residential uses. Review of nonresidential projects should ensure that the following design issues are minimized or avoided in projects that abut residential areas:

1. Inappropriate building scale and/or placement on the lot.

2. Excessive glare or excessive impacts from light sources onto adjacent properties.

3. Excessive noise generated from freight and waste management activities during night hours.

4. Excessive air pollutant emissions from freight trucks and large expanses of parking lot areas.

Goal CD-4: Minimize the extent of development in the hillsides and mitigate any adverse consequences associated with urbanization.

CD-4 Policies
● CD-4.1 Development Level. Maintain low density/intensity land use designations in the hillside areas.
● CD-4.2 Constraints. Base allowable development on the ability of infrastructure, landform, physical constraints, and emergency response capabilities to support new development.
● CD-4.3 Natural Grading. Encourage natural grading techniques that blend with existing topography; grading should use rounded contours on slopes to minimize disturbance.

Encourage the preservation of the physical shape of the hillsides and views where feasible.
● CD-4.4 Hillside Zoning Ordinance. Enforce the City’s Hillside Zoning Ordinance, which establishes standards for permitted density on slopes, subdivision design, ridgeline preservation, grading, retaining walls, and other requirements. ● CD-4.5 Regional Coordination. Coordinate with Orange County and emphasize the City’s need to participate in the development review process of projects proposed in surrounding unincorporated areas. Work to ensure that such developments proceed consistent with City standards.
● CD-4.6 Natural Fire Breaks. Preserve natural fire breaks through designated Open Space land use.

Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)

● CD-4.7 Building Design. Building materials and colors for development in the hillsides should blend with the natural landscape.
● CD-4.8 Clustered Development. Incentivize clustered development within hillside areas by directing new development to previously disturbed or less environmentally sensitive areas to preserve natural landforms, open space, and visual character.

CD-4 Actions
● CD-4a Require a constraints analysis for properties zoned Hillside Residential. The constraints analysis shall include a detailed description and mapping of slopes, geologic factors, areas prone to flooding, and any sensitive biological resources. ● CD-4b Require continued implementation of the City’s Hillside Zoning Ordinance. ● CD-4c Establish objective development criteria for all new development zoned Hillside Residential and designated High or Very High Fire Hazard Severity Zones to enhance fire resilience, reduce risk to life and property, and ensure consistency with applicable safety regulations and best practices.
● CD-4d Explore and analyze the feasibility of establishing a Transfer of Development Rights (TDR) program to promote conservation for City Council consideration.

Goal CD-5: Provide sufficient levels of water, sewer, and storm drain service throughout the community.

CD-5 Policies
● CD-5.1 System Capacity. Coordinate the demands of new development with the capacity of water, sewer, and storm drain systems.
● CD-5.2 Master Plans. Implement the City’s water, sewer, and drainage master plans to address known deficiencies and support improvements that add resiliency and reliability to City infrastructure.
● CD-5.3 Development Impacts. Require that new developments fund their fair-share of costs associated with improvements to public infrastructure necessitated by the new development. ● CD-5.4 Funding. Work with developers to ensure that adequate funding and improvements for required infrastructure is provided or ensured via bonds. ● CD-5.5 Sewer Discharge Elimination. Minimize damage to wastewater collection and downstream treatment systems by preventing discharge of materials that are toxic or which would obstruct flows.

Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)

● CD-5.6 Stormwater Treatment. Pursue treatment and disposal methods which, to the maximum extent feasible, provide for further beneficial use of stormwater runoff and allow beneficial uses of land or water receiving the effluent. ● CD-5.7 Stormwater Overflow. Continue to investigate and carry out cost-effective methods for reducing storm water flows into the wastewater system. ● CD-5.8 Stormwater Quality. Update and enforce Brea’s standards for the quality of stormwater discharged to the system.
● CD-5.9 Waste Reduction and Recycling. Continue to enhance solid waste, recycling, organics recycling, and construction and demolition programs for all community members to ensure compliance with California recycling legislation and support programs that prioritize waste reduction and recycling in order to minimize landfill disposal and reduce greenhouse gas emissions.
● CD-5.10 Infrastructure Expansion. If analysis shows capacity concerns on infrastructure, limit the extension of public services and utility infrastructure to reduce increasing fire risks and minimize other environmental impacts.

CD-5 Actions
● CD-5a Implement the Capital Improvement Program incorporating the following range of public facilities:
o Street Improvements
o Traffic Safety Enhancements
o Storm Drain Improvements
o Water Improvements
o Sewer Improvements
o Building and Parks & Recreational Facility Improvements o Golf Course Improvements
o Other major capital investments needed to sustain the City’s development and operations
● CD-5b Regularly review mechanisms for funding and phasing of new infrastructure and bring recommendations to the City Council for consideration. ● CD-5c Create and distribute digital and print educational materials to support sustainable practices, including the implementation of three-cart collection systems to increase diversion of solid waste from landfills.

Goal CD-6: Promote balanced growth with supporting public services infrastructure.

Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)

CD-6 Policies
● CD-6.1 Development and Services. Balance quality development with adequate and equitable distribution of services, resources, and amenities throughout the City. EJ ● CD-6.2 Land Use and Transportation. Integrate land use and transportation planning to provide adequate transportation system service standards. EJ ● CD-6.3 Local Services. Monitor and maintain service level standards for public services and infrastructure.
● CD-6.4 Adequate Services. Ensure that new development is in balance with the provision of services and/or funding. EJ
● CD-6.5 Growth Pattern. Strongly encourage new development in infill locations in a balanced and efficient pattern that reduces sprawl, preserves open space, and creates convenient connections to other land uses and transportation facilities. ● CD-6.6 Local Employment. Support programs that match Brea residents with local jobs to reduce long commutes.
● CD-6.7 Transportation Facilities. Assist in the provision of adequate regional and local transportation facilities.
● CD-6.8 Interregional Cooperation. Cooperate with other agencies to address regional issues and opportunities related to growth, transportation, infrastructure, and other planning issues.
● CD-6.9 Alternative Modes of Travel. Promote the expansion and development of alternative methods of transportation.
● CD-6.10 Employment Proximity. Encourage the development of housing within close proximity to jobs and services.

CD-6 Actions
● CD-6a Cooperate with regional agencies to improve regional services and air quality by actively participating in the development of the Southern California Association of Government’s regional comprehensive plan and its sub-regional plan component for Orange County.

Mobility Element
Goal M-1: Maintain an effective regional transportation network.

Brea 2050 Public Hearing Draft General Plan Goals Policies and Actions (April 2026, Version 2)