US Department of Transportation
3.11 Speed Cushion
DESCRIPTION AND GENERAL PURPOSE
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A speed cushion consists of two or more raised areas placed laterally across a roadway (see Figure 3.11.1 ). The height and length of the raised areas are comparable to the dimensions of a speed hump. The primary difference is that a speed cushion has gaps (often referred to as "cutouts") between the raised areas to enable a vehicle with a wide track (e.g., a large emergency vehicle, some trucks, some buses) to pass though the feature without any vertical deflection.
Another difference between a speed cushion and a speed hump is the common practice for the top of the speed cushion to be level. Like a speed hump, the profile of a speed cushion is gentle enough to provide a comfortable ride when traversed at a speed of approximately 20 to 25 MPH.
[A speed cushion is also known as a speed lump, speed slot, and speed pillow.] The cutouts in the speed cushions are positioned such that a passenger vehicle cannot pass it without traveling over a portion of the raised pavement.
A speed cushion is often a preferred alternative to a speed hump on a primary emergency response route or on a transit route with frequent service. [Two field studies of three speed cushions measured reductions between 5 and 7 mph for 85th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) https:ll www.highways.dot.gov/safetylspeed-managementlengineering-speed- management-countermeasures l
Figure 3.11.1. Speed Cushion with Passage that Straddles Centerline (Source: Jeff Gulden)
APPROPRIATE APPLICATION
Appropriate Application -Speed Cushion
Type of Street
Intersection or
Roadway
Segment
Roadway
Cross-Section
Generally appropriate for both local and collector streets Placed at a midblock location; as an example, Pennsylvania recommends a distance of 150 feet from an unsignalized intersection and 250 feet from a signalized intersection
Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet
Can be used on a single-lane one-way or two-lane two-way street (examples are shown in Figures 3.11.2 and 3.11.3)
Typically installed with an urban cross-section (i.e., curb and gutter)12