- This article or section should be merged with speed bump
See also: Speed Bump, a comic strip.
A speed hump (in British English sometimes a sleeping policeman) is a traffic calming measure. It consists of a bump in the road, designed to encourage oncoming vehicles to slow down in order to pass safely. Speed humps may be circular, parabolic, or sinusoidal and have gaps near the curb to allow drainage. The speed at which a hump can be taken safely decreases with its slope. Humps range from 10 to 24 feet long (in the direction of travel), and range in height from 2 5/8" to greater than 4" in some cities.
Speed humps are sometimes referred to as speed bumps, but most traffic engineers prefer to use that term to refer to the shorter, more abrupt bumps that are commonly found in parking lots, alleys, and other places where prevaling vehicle speeds are expected to be low. Their use on roads is not as widespread, but are often sought by residents who are concerned about the volume of commuter traffic using their street are a bypass route to save time over using a nearby congested arterial street. Additionally, newer vehicles with modern suspension and safety equipment give drivers the impression that they are travelling at a slower speed than they actually are. Many neighborhood traffic management studies have shown that as much as 75% of the perceived "commuter" speeding can actually be attributed to the local residents themselves, often unware that they were travelling as fast as they were.
Speed humps have been proven to reduce measured critical speeds (the speed at which 85% of the vehicles are traveling at or below) by at least 5 miles per hour (10 kilometers per hour). However, their widespread use is somewhat controversial as they can cause vehicle damage if taken at too great a speed, and cause some discomfort for some sensitive vehicle users. Some are hard to negotiate in vehicles with low ground clearance, such as sports cars, even at very slow speeds. Poorly designed speed humps (too tall, too sharp an angle for the expected speed) are often to blame, rather than the concept in general.
Vehicles with high ground clearance and softer springing, such as sport utility vehicles and other nominally off-road vehicles, negotiate speed humps much more comfortably even at greater speeds than regular passenger cars. Thus, there is some reason to believe that the prevalence of speed humps encourages the SUV phenomenon, and certainly that phenomenon reduces the speed hump's effectiveness as a traffic calming measure.
Some speed humps have been criticised as being an impediment to emergency vehicles, particularly ambulances, where EMTs may be working on a patient. As a result of this concern, many cities do not install speed humps on designated primary emergency response routes.
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