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Human Factors

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Safety Subject Information:   

SPEEDBUMPS:

Speedbumps should be avoided wherever possible. There is often a clamor by residents to have them installed in response to fast traffic. This clamor should be resisted.

Common sense says that speedbumps are effective in reducing speed. Many drivers will tend to slow down to traverse them. The people who need them most will not.

For a physical speed limiting device to be effective, the motivation to reduce speed must be more imperative with the increase in speed. With speed bumps, the discomfort to drivers decreases significantly with increasing speed. The higher speed causes the impact with the bump to be almost completely absorbed by a vehicle`s suspension without the appropriate jolt being transferred to the body and passenger compartment of the vehicle.

By and large the folks that are in need of the perceived restriction imposed by speed bumps are the same ones whose familiarity with the handling characteristics of their vehicles will encourage them to hit the speedbumps at full speed.

Those who travel slowly anyway will be encouraged to ease gently over the speedbumps while slowing to a crawl because at low speed all of the vertical displacement caused by the speedbump will be imparted to the body of the vehicle and the passenger compartment.

Less competent drivers who might miss seeing the low profile of the speedbump can loose control of their vehicles. This could cause a catastrophe far greater than a mere fall.

Heavy vehicles and emergency equipment can become dangerously unstable after hitting a speedbump. This is particularly dangerous in the case of fire equipment where riders may not be fully secure in the vehicle. A classic encounter involves the pumper company responding to an emergency with two or three firefighters riding on the tail platform of a pumper truck.

A study was conducted by the City of San Jose to determine the actual effects of speedbumps on emergency equipment. The city determined that the advantages of speedbumps are far outweighed by the danger.

Pedestrians will be presented with a classic trip, slip, stumble-and-fall hazard. The low profile of the typical speedbump presents an obstacle that may not visually perceptible to pedestrians. The sloped face and vertical rise of the speedbump will, however be sufficient to cause falls.

If speedbumps are used (they should not be), there are some precautions that must be taken to ensure that they will not pose a danger to pedestrians. They must be well lit. Their surfaces must be treated to make them non-slip, and they must be distinctly, plainly, and appropriately marked for visibility. They should be installed well away from likely pedestrian paths.  Some of these requirements are in ASTM Standards.

Copyright 2000 - 2011, Jay W. Preston.  Distribution permission granted when this notice is printed in full.  For questions or comments: contact prestonoidaol.com.  The J-P, Plus Design and SAFETYBIZ. are registered service marks of Jay William Preston. Permission for use of specific Safety Subject Information is only granted when this notice is printed in full and Preston has been contacted by phone, fax, or email prior to use.