What Is a Speed Cushion?
A speed cushion is a traffic-calming device that sits across a travel lane, typically made of rubber, plastic, asphalt, or concrete. It is narrower than a speed hump and positioned so that passenger cars straddle it, while wider vehicles such as ambulances, fire trucks, and buses can drive over it with minimal vertical deflection. This design lets the cushion reduce speeds on residential streets and school zones without significantly delaying emergency response.
- What Is a Speed Cushion?
- How Speed Cushions Slow Traffic
- Materials and Construction Types
- Typical Dimensions and Placement
- Where Speed Cushions Are Used
- Speed Cushion vs Speed Hump vs Speed Table
- Benefits of Speed Cushions
- Limitations and Common Concerns
- Design and Installation Considerations
- Maintenance and Longevity
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How Speed Cushions Slow Traffic
Speed cushions force drivers to slow down because the raised sections create discomfort and vehicle pitch when traversed at higher speeds. Unlike speed humps, which span the full width of the road and force all vehicles to slow down, cushions leave space on either side so large vehicles can stay flat. The result is a self-selecting calming effect: private cars and light trucks decelerate, while emergency vehicles maintain operational speed.
Materials and Construction Types
Speed cushions are manufactured from several materials, each suited to different budgets, traffic volumes, and climate conditions:
- Rubber and recycled plastic — Lightweight, easy to install, and often used in temporary or low-volume settings. They are durable but can degrade faster under heavy UV exposure or extreme cold.
- Asphalt and concrete — Permanently built into the road surface. These last longer and handle heavy traffic well, but they require more labor and roadwork to install and adjust.
- Pre-cast composite — A hybrid that combines durability with easier replacement. These are common in cities looking for a long-term but modular solution.
Typical Dimensions and Placement
Most speed cushions are about 3 to 4 feet wide and 3 to 6 inches tall, with a length of 10 to 14 feet per unit. They are spaced in a series down a block, usually every 150 to 250 feet, depending on the desired speed reduction and street geometry. Placement is typically centered in the travel lane or offset to discourage drivers from swerving around them into adjacent bike or pedestrian spaces.
Where Speed Cushions Are Used
Municipalities install speed cushions on residential streets, near schools, in front of parks, and along routes with mixed traffic. They are common in suburban neighborhoods where speed limits are low but cut-through traffic is a concern. Because they do not block emergency vehicles, they are often preferred over speed humps in areas served by fire stations or hospitals.
Speed Cushion vs Speed Hump vs Speed Table
Understanding the differences helps planners choose the right calming measure:
| Feature | Speed Cushion | Speed Hump | Speed Table |
|---|---|---|---|
| Width | Narrow (covers one lane) | Full lane width | Full lane width, longer and flatter |
| Emergency vehicle impact | Low (wide vehicles straddle) | High (all vehicles slow) | Moderate |
| Comfort for passenger cars | Moderate | High discomfort at speed | Low discomfort |
| Typical height | 3–6 inches | 3–4 inches | 3–4 inches |
| Best use case | Residential, mixed traffic | Low-speed residential | Longer calming zones, downtown |
Benefits of Speed Cushions
- Effective at reducing speeds on residential streets without causing major delays.
- Allow emergency vehicles, buses, and wider trucks to pass unimpeded.
- Can be installed quickly, especially modular rubber versions.
- Low maintenance for prefabricated units; asphalt versions integrate smoothly into the road.
- Visually signal to drivers that a pedestrian-friendly zone is ahead.
Limitations and Common Concerns
Speed cushions do not slow all vehicles equally. Drivers in the adjacent lane may not be affected, and some may try to pass a cushion on the shoulder, which can create conflicts with cyclists or parked cars. On streets with frequent bus or delivery routes, repeated vertical deflection can cause discomfort inside the vehicle and increase maintenance needs at mounting points. Noise from repeated crossing is also a consideration, especially with rigid materials.
Design and Installation Considerations
Before installing speed cushions, transportation engineers evaluate the 85th percentile speed, traffic volume, crash history, and the mix of vehicle types. Local regulations and public input often shape the decision. Proper signage, road markings, and advance warnings help drivers anticipate the cushion and reduce the risk of sudden braking or swerving.
Maintenance and Longevity
Rubber and plastic cushions require periodic inspection for cracking, fading, or shifting. Asphalt and concrete cushions should be checked for settlement and surface deterioration. Reflective markings or painted stripes improve visibility at night and in poor weather. Well-maintained cushions retain their calming effect and continue to protect pedestrians and residents for many years.