Speed humps are vertical traffic control measures. They are paved (usually asphalt) and approximately three to four inches high at their center, and extend the full width of the street with height tapering near the drain gutter to allow unimpeded bicycle travel. Speed humps should not be confused with the speed “bump” that is often found in mall parking lots. There are several designs for speed humps. A “speed table” is a term used to describe a very long and broad speed hump, or a flat-topped speed hump, where sometimes a pedestrian crossing is provided in the flat portion of the speed table.
The traditional 12-ft hump has a design speed of 15 to 20 mph, 14-ft hump a few mi/h higher, and a 22-ft table has a design speed of 25 to 30 mph. The longer humps are much gentler for larger vehicles. The speed table can either be parabolic, making it more like a speed hump, or trapezoidal. Speed tables can be used in combination with curb extensions where parking exists. Speed humps can also be designed with two, one-foot slots to allow for vehicles with wide wheelbases such as buses and emergency vehicles to pass through them without having to go over the measure. These are typically called “speed cushions.”
In general, speed humps are a device of last resort. Other traffic calming solutions should be considered first. However, they may be the best solution is some situations, especially on long, straight residential streets where there are few intersections and no other visual cues to slow motorists.
Vertical measures tend to have the most predictable speed reduction impacts and are best used on local streets. Speed tables can also enhance the pedestrian environment at pedestrian crossings.
- Do not use if on a sharp curve.
- If the street is a bus route or primary emergency route, the design must be coordinated with operators. Usually, some devices are acceptable if used prudently — one device may be appropriate and may serve the primary need (e.g., if there is a particular location along a street that is most in need of slowing traffic and improving pedestrian conditions).
- The aesthetics of speed humps and speed tables can be improved through the use of color and specialized paving materials.
- Noise may increase, particularly if trucks use the route regularly.
- May create drainage problems on some streets.
- Speed humps and tables should be properly designed and constructed to reduce the chance of back problems or other physical discomfort experienced by vehicle occupants. Tight tolerances are required during construction.
The cost for a speed hump can range from approximately $700 to $6,900, depending on the height, width of the road, drainage conditions, and design. An average cost is approximately $2,600. The cost for a speed table can range from approximately $2,000 to $20,000.