Advanced Mobility Group | 3003 Oak Road, Suite 100, Walnut Creek, Ca.
Redefining Mobility.
June, 24 2026
City of Santa Maria
Ms. Zoe Click, Associate Engineer
Transmitted Electronically
Reference: West Stowell Road and Black Road Warrant Evaluation and key findings Summary
Summary Of Findings
The intersection of West Stowell Road and Black Road is located in a rural area characterized by relatively high operating speeds, limited roadside development, and driver expectancy of uninterrupted travel along the major roadway. The collision history demonstrates a recurring pattern of right-angle and right-of-way-related crashes, including injury collisions and a recent fatal pedestrian crash. These crash types are among those most commonly addressed through the implementation of all-way stop control.
The recently collected turning movement counts indicate that the intersection experiences sufficient traffic activity on both the major and minor approaches to create recurring conflict opportunities. While traffic volumes alone may not independently justify signalization, the combination of traffic demand, documented crash history, intersection geometry, and rural operating characteristics supports the implementation of enhanced intersection control measures.
The collision history reveals a persistent pattern of driver decision-making errors, including failure-to- yield and right-of-way violations. Given the severity of the crashes, the demonstrated conflict patterns, and the potential for future severe collisions, implementation of a three-way stop control is considered an appropriate and cost-effective safety countermeasure.
Engineering Justification
The recommended three-way stop control is justified by the combination of:
• A documented history of broadside and right-of-way-related collisions. • Multiple injury crashes and one fatal pedestrian collision. • Traffic volumes that create recurring crossing and turning conflicts. • Rural roadway characteristics and higher operating speeds. • The need to reduce approach speeds and improve driver awareness. • The ability of all-way stop control to directly address the predominant crash types observed at the intersection.
The recommended improvements are expected to reduce the likelihood and severity of future angle collisions, improve driver compliance, lower approach speeds, and enhance overall intersection safety for motorists, pedestrians, bicyclists, agricultural vehicles, and heavy trucks using the corridor.
Attachment C
June 24, 2026
Reference: West Stowell Road and Black Road Warrant Evaluation and key findings Summary
Advanced Mobility Group | 3003 Oak Road, Suite 100, Walnut Creek, CA
Crash History Evaluation (2021 – 2025)
Overview
A review of reported collisions occurring at the intersection of West Stowell Road and Black Road during the five-year period from January 1, 2021 through December 31, 2025 was conducted to identify crash patterns and determine whether additional traffic control measures are warranted.
The review indicates a recurring pattern of angle and right-of-way related collisions that are characteristic of intersections where motorists fail to recognize conflicting traffic movements or incorrectly judge available gaps. The crash history also includes a fatal pedestrian collision, further elevating the safety significance of the intersection.
Five – Year Collision Summary
Although the intersection does not exhibit a concentration of crashes within a single year as shown is Figure 1, the continued occurrence of broadside crashes throughout the study period indicates an ongoing safety concern.
Figure 1: Crash History
The majority of crashes involved crossing conflicts, failure-to-yield conditions, or improper turning movements. These collision types are commonly addressed through all-way stop control because the treatment requires all vehicles to stop and establish right-of-way prior to entering the intersection.
Attachment C
June 24, 2026
Reference: West Stowell Road and Black Road Warrant Evaluation and key findings Summary
Advanced Mobility Group | 3003 Oak Road, Suite 100, Walnut Creek, CA
The presence of both severe injury and fatal collisions demonstrates that crashes occurring at this intersection have the potential for significant consequences despite the relatively rural setting.
Pedestrian Safety Considerations
The collision record includes a fatal pedestrian crash that occurred during the study period. While pedestrian activity levels are generally lower than those found in urban areas, the occurrence of a fatal pedestrian collision indicates that vulnerable roadway users are present and exposed to risk at the intersection.
Implementation of three-way stop control would be expected to reduce approach speeds and increase driver attention, thereby improving conditions for pedestrians, bicyclists, and other vulnerable roadway users.
Crash Pattern Assessment
The collision history demonstrates several recurring characteristics:
• Repeated broadside collisions.
• Multiple right-of-way violations.
• Crashes involving crossing movements.
• Injury-producing collisions.
• A fatal pedestrian crash.
• Collision patterns consistent with inadequate driver recognition of conflicting traffic.
These recurring patterns indicate that existing traffic control devices are not fully mitigating conflicts between intersecting traffic streams.
Safety Conclusion
The five-year collision history reveals a persistent pattern of correctable angle crashes, right-of-way violations, and severe crash outcomes. When combined with the recently collected turning movement counts and the rural operating environment, the crash history supports the installation of three-way stop control and associated warning devices to improve driver awareness, reduce approach speeds, and reduce the likelihood of future severe collisions.
Traffic Demand and CA-MUTCD Warrant Evaluation
The turning movement count data collected at the intersection of West Stowell Road and Black Road indicate that the intersection experiences consistent traffic demand on all approaches during both the AM and PM peak periods. The major street, West Stowell Road, carries the majority of traffic through the intersection, with peak-hour through volumes exceeding 470 vehicles per hour as shown in Figure
2. At the same time, Black Road generates meaningful entering traffic and turning movements that require drivers to identify acceptable gaps in major-street traffic before entering or crossing the intersection. These traffic conditions create recurring opportunities for crossing and turning conflicts, particularly during peak travel periods.
The California Manual on Uniform Traffic Control Devices (CA-MUTCD) recognizes that all-way stop control may be appropriate where traffic volumes on the major and minor approaches create operational and safety concerns, particularly when combined with a history of correctable crashes. The Attachment C
June 24, 2026
Reference: West Stowell Road and Black Road Warrant Evaluation and key findings Summary
Advanced Mobility Group | 3003 Oak Road, Suite 100, Walnut Creek, CA
traffic counts demonstrate that the intersection experiences sufficient demand to generate frequent vehicle interactions, while the crash history reveals a recurring pattern of right-angle collisions, right-of- way violations, and injury-producing crashes. Although no single traffic volume threshold independently mandates all-way stop control, the combination of substantial major-street traffic, recurring minor-street entry movements, documented crash experience, and the rural operating environment provides strong engineering justification for the installation of three-way stop control.
Furthermore, the rural character of the intersection contributes to higher approach speeds and reduced driver expectancy of a stop-controlled condition. As a result, the recommended three-way stop control should be accompanied by enhanced warning devices, including oversized STOP signs, flashing red STOP enhancements, STOP AHEAD warning signs, and extended channelization striping on all approaches. Together, these improvements will improve driver awareness, reduce approach speeds, clarify right-of-way assignments, and address the primary crash patterns identified during the safety evaluation.
Figure 2: Traffic Demand
Recommended Improvements
It is recommended that the City install three-way stop control at the intersection of West Stowell Road and Black Road.
The proposed all-way stop treatment should include the following design elements:
Attachment C
June 24, 2026
Reference: West Stowell Road and Black Road Warrant Evaluation and key findings Summary
Advanced Mobility Group | 3003 Oak Road, Suite 100, Walnut Creek, CA
1. Installation of STOP signs on all approaches in accordance with the California MUTCD.
2. Use of oversized STOP signs ranging from 36-inch to 48-inch diameter, as appropriate, to improve conspicuity and driver recognition in the rural environment.
3. Installation of flashing red LED-enhanced STOP signs or supplemental flashing red beacons mounted above the STOP signs as permitted by the California MUTCD to further increase driver awareness and compliance.
4. Installation of STOP AHEAD warning signs on all approaches due to the rural setting, higher approach speeds, and the likelihood that motorists may not anticipate a stop-controlled intersection.
5. Installation of advance warning pavement markings where appropriate to supplement the STOP AHEAD signs.
6. Reconstruction and enhancement of pavement striping on all approaches to provide positive channelization and improved driver guidance.
7. Extension of centerline and edge-line channelization for a minimum distance of approximately 200 feet in advance of the intersection on each approach. The channelization should include:
• Double yellow centerline striping.
• Reflective pavement markers where appropriate.
• Edge lines to better define travel paths.
• Tapered approach markings guiding vehicles into the stop-controlled intersection.
8. Upgrade of all stop bars and pavement legends to current California MUTCD standards.
9. Installation of high-intensity retroreflective sign sheeting and upgraded sign supports consistent with current safety standards.
Best regards,
Rafat Raie, T.E.
Principal
Advanced Mobility Group
Attachment C