Why are speed cushions split into segments?

The wheel-track gaps between segments allow fire engines, aerial ladder trucks, and ambulances to straddle the cushion at near-normal speed while passenger cars (with narrower track width) hit the cushion segments. This is the design feature that distinguishes a cushion from a speed hump or speed bump. Without the gaps, fire response would be delayed unacceptably.

How wide is the wheel-track gap?

The wheel-track gap is sized to the rear-axle outside-to-outside dimension of the local fire department's apparatus. North American fire engines typically run 78 to 84 inches; aerial ladder trucks similar. Some Oregon fire departments specify 1.85 meters (72 to 73 inches) for older European-spec apparatus. Always confirm with the local fire marshal before specifying.

How tall is a speed cushion?

A standard speed cushion is 3 to 3.5 inches tall, the same as a speed hump. ITE Traffic Calming Manual Chapter 3 documents this as the height that produces 85th-percentile speed reduction to 18 to 22 mph while remaining within passenger-car suspension tolerance. Heights below 2.75 inches do not produce reliable speed reduction; heights above 3.5 inches risk vehicle damage.

Are speed cushion dimensions standardized nationally?

Speed cushion dimensions are not federally mandated. ITE and FHWA publish recommended ranges, but the wheel-track gap specifically is set by the local fire department because apparatus axle widths vary. NFPA 1141 chapter 5 provides the framework municipalities use to evaluate proposals. Always verify current requirements with your local jurisdiction; this article reflects May 2026 guidance.

Speed Cushion Dimensions: Standard Size & Wheel-Gap Spec (2026)

A standard speed cushion segment is 6 feet long by 6 feet wide by 3 inches tall, installed in groups of 2 or 3 segments per cushion to leave 1.85-meter (72 to 73 inch) wheel-track gaps that match fire-apparatus rear axle width. The Federal Highway Administration's Traffic Calming ePrimer Module 3.4 and the Institute of Transportation Engineers (ITE) Traffic Calming Manual, Chapter 3, document these dimensions. The wheel-track gap is the dimension that distinguishes a speed cushion from a speed bump or speed hump.

What Are the Standard Speed Cushion Dimensions?

Dimension	Standard value	Notes
Cushion segment length (travel direction)	6 to 7 feet	Equivalent to a long speed bump or short speed hump
Cushion segment width (across travel)	6 feet	Per segment
Cushion segment height	3 to 3.5 inches	Same as a speed hump
Wheel-track gap	1.6 to 1.85 meters (63 to 73 in)	Sized to local fire-apparatus axle width
Total cushion footprint width	13 to 18 feet across travel lane	Depends on lane count and segment configuration
Number of segments per cushion	2 to 4	Most common is 3 (2 outside, 1 center)

The exact dimensions vary by manufacturer and by jurisdiction. The wheel-track gap is the dimension that requires local fire-marshal verification before specification.

Why Is the Wheel-Track Gap the Critical Dimension?

A speed cushion's purpose is to slow passenger cars while letting fire engines and ambulances pass at near-normal speed. Passenger cars have rear-axle track widths in the 50 to 65 inch range, narrower than fire apparatus. Fire engines and aerial ladder trucks typically have rear-axle outside-to-outside dimensions of 78 to 84 inches. A cushion with wheel-track gaps sized to the fire-apparatus width lets the truck straddle the cushion (with one tire path on each side of the device), while the narrower-track car hits the cushion segments full-on.

The USFA Emergency Vehicle Safety Initiative publishes ladder-truck axle data many municipal fire departments use as their wheel-track gap reference. NFPA 1141 chapter 5 on fire-protection infrastructure for residential development provides the framework municipalities use to evaluate whether a proposed cushion preserves required fire-apparatus access. Cushions installed without fire-marshal sign-off on the wheel-track gap routinely fail department review and require re-installation.

Cushion Segment Configurations by Lane Count

Lane scenario	Typical configuration	Wheel-track gap count
One-lane residential street	2 outside segments, 1 wheel-track gap	1
Two-lane residential street	3 segments per direction, 2 outside-lane gaps	2 per direction
Two-lane bidirectional with center turn lane	3 segments per direction, gaps aligned across centerline	2 per direction
Four-lane collector	4 segments per direction, 2 outside-lane gaps + 1 inside-lane gap	3 per direction

The configuration choice depends on traffic mix and on whether the street is a designated fire-access route. Streets that are not on fire-access routes are sometimes treated with speed humps instead of cushions, which removes the wheel-track gap requirement entirely. For a fuller decision framework see how do speed cushions work.

Cushion Height Guidance

The 3 to 3.5 inch standard height is the same as a speed hump and the same as a typical 3-inch speed bump. ITE Traffic Calming Manual Chapter 3 documents this as the height that produces meaningful 85th-percentile speed reduction (typically to 18 to 22 mph) while remaining within passenger-car suspension tolerance.

Heights below 2.75 inches do not produce reliable speed reduction. Heights above 3.5 inches risk passenger-car damage and exceed published ITE recommendations. Always verify current local jurisdiction guidance before specifying a non-standard height.

Wheel-Track Gap Reference Values (Common Oregon Fire Apparatus)

The following are reference values only. Always confirm with the local fire department before specifying.

Apparatus class	Typical rear-axle outside-to-outside	Recommended gap
Type 1 engine (typical)	80 to 84 inches	84 inches (2.13 m)
Type 1 engine (urban)	78 to 80 inches	80 inches (2.03 m)
Aerial ladder truck (typical)	78 to 82 inches	82 inches (2.08 m)
Quint apparatus (combo engine + ladder)	80 to 84 inches	84 inches (2.13 m)
Heavy rescue	78 to 82 inches	82 inches (2.08 m)
Tower truck (Tigard / Tualatin Valley F&R example)	72 to 73 inches	73 inches (1.85 m)

The 1.85-meter gap commonly cited in FHWA reference documents reflects an older European fire-apparatus standard; many North American departments now require 80+ inches.

How the Dimensions Combine with the Cross-Section

A typical 3-segment cushion on a 24-foot residential street looks like:

2-foot lane edge (curb buffer or gutter pan)
4-foot outside cushion segment
6-foot outside-lane wheel-track gap
6-foot center cushion segment
6-foot inside-lane wheel-track gap (mirror)
4-foot outside cushion segment
2-foot lane edge

This places one wheel-track gap in each direction's outside lane (where fire trucks travel) while ensuring no through-path exists for a passenger car. Adjusting segment widths fits different lane counts and curb-to-curb dimensions.

From Our Crew

On a Tigard fire-access greenway in late 2024, Cojo installed three modular rubber speed cushions configured to a 1.85-meter wheel-track gap. Tualatin Valley Fire & Rescue specified the gap from their tower-truck axle measurement; the field crew verified the gap on each cushion before drilling anchor holes. We documented the as-built gap measurements on a layout drawing and submitted the drawing to the city engineering department after install, which is standard close-out practice for any fire-access traffic-calming work.

How Do Cushion Dimensions Compare with Speed Humps and Tables?

Device	Length (travel)	Width (across)	Height	Wheel-track gaps
Speed bump	1 to 3 feet	Full lane	3 to 4 inches	None
Speed hump	12 to 14 feet	Full lane	3 to 4 inches	None
Speed cushion	6 to 7 feet (per segment)	6-foot segments + gaps	3 to 3.5 inches	Yes, sized to fire apparatus
Speed table	22 feet (10-ft flat top + 6-ft ramps)	Full lane	3 to 4 inches	None (use full width)

The cushion is the only device on this list that uses wheel-track gaps to preserve emergency-vehicle access. For speed table dimensions see the sibling article in the cluster.

What Reference Documents Govern Speed Cushion Dimensions?

ITE Traffic Calming Manual, Chapter 3 (Speed Cushions section)
FHWA Traffic Calming ePrimer, Module 3.4
NFPA 1141, Chapter 5 (fire-protection infrastructure for residential development)
IFC Section 503 (fire-apparatus access roads)
Local fire department apparatus axle specifications (always verify directly)

Always verify current requirements with your local jurisdiction. This article reflects May 2026 published guidance.

Need Speed Cushion Specification Help?

Cojo coordinates fire-marshal review and dimensional sign-off on every cushion install across the Oregon I-5 corridor. We document as-built wheel-track gaps on the project drawing and submit close-out documentation to the city engineering department. For the install procedure see how to install a speed cushion, and for the broader product context see the speed cushions guide. For Salem-area installs see Speed Cushion Installation Salem or pair installation with our asphalt maintenance services. Get a custom quote.