Highway Speed Limits Should be set to the 85th Percentile Speed.
WARRENDALE, Pa., Feb. 15 /PRNewswire/ -- The following was released by the Society of Automotive Engineers:
Can lowering speed limits increase accidents and accident severity? And raising them have little or no effect? A recent study performed to investigate the relationship between speed limits and accident rates found that in the case of Interstate Highways, the answer is yes.
These and other results of the study will be presented by George Z. Libertiny, Ford Motor Company (NYSE: F) from 2-2:30 p.m., Tuesday, February 27 at the 1996 SAE International Congress and Exposition, Room D3-28, Cobo Center, Detroit.
On any given road, 85 percent of drivers travel at a speed that they find appropriate to the road, regardless of the posted speed limit. Some states use this "85-percentile" average speed in setting their speed limits. Yet, according to a Federal Highway Safety Administration report " ... the majority of speed limits are posted below the average speed of traffic."
When drivers encounter speeds they find unreasonably low, some will travel at the lower speed. But if most stay at higher speeds, faster moving cars are constantly overtaking and passing the slower-moving ones. This increases danger to both vehicles, since danger increases as the speed difference between vehicles increases.
Furthermore, if highway speed limits are set unreasonably low and are enforced through tickets to speeders, more motorists opt for secondary local roads with similar speed limits. These roads may be more convenient, but they have an accident rate nearly twice as high and an accident-fatality rate between two and three times that of the Interstate Highways.
Thus, the net effect of reducing speed limits may actually increase the number of speeding drivers and serious accidents on all roads.
On the other hand, while rural-interstate speed limits have been raised to 65 mph and traffic density on those roads has increased, the fatality rate on these roads has actually decreased. And according to a separate Federal Highway Administration study, raising speed limits does not increase speeding or the number of accidents.
The study suggests several ways that accidents can be reduced: 1.) interstate express roads should have speed limits representing road and tire design limitations; 2.) speed limits on these roads should be set by individual states and should reflect the effects of local traffic conditions and road quality; 3.) separate speed limits should be set for nighttime and wet roads; 4.) emergency services to rural roads should be improved to decrease the time it takes to get an accident victim to the hospital; 5.) seat belt laws should be strictly enforced; and 6.) laws regarding alcohol and other drug usage should be strengthened and diligently enforced.
For further information on the SAE International Congress and Exposition, which runs February 26-29, contact Sandi Kline at 412-772-8547.
CO: Society of Automotive Engineers
ST: Pennsylvania, Michigan
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