One benefit of enforcing speed limits is that fewer car accidents occur when vehicles are traveling at about the same speed.

Do Lower Speeds Really Mean Fewer Accidents?

Speed limits perform several important functions: reducing disparities in speed, decreasing the frequency of auto accidents, and providing a basis for enforcement of penalties against those who endanger others.

Observing the speed limit is much more than driving the posted speed. It means driving according to the road conditions. When it is rainy, foggy, or icy; when road construction is underway; or when traffic is heavy, you must adjust your speed accordingly.

On the other hand, there are benefits to allowing motorists to travel as fast as they can safely do so, according to the Federal Highway Administration. Speed reduces travel times, increases mobility, and increases economic productivity through lower transportation and inventory costs and larger market areas.

Colorado Speed Limits

Under Colorado law, there are two types of speed limits:

  • Absolute speed limits, which under no circumstances can legally be exceeded, are 65 mph on open highways and 75 mph on rural interstate routes.
  • Prima facie speed limits are those considered to be reasonable and prudent, and allow a driver to exceed them if it is safe to do so. In Colorado, the basic prima facie speed limits are 20 mph on narrow, curving mountain roads; 25 mph in business districts; 30 mph in residential districts; and 40 mph on sweeping mountain highways.

Lower Speed Limits Not Necessarily Safer

Research has found no significant reduction in the number of automobile accidents when speed limits are set below the reasonable pace maintained by most drivers. In fact, speed limits that are unreasonably low make the behavior of the majority of drivers illegal, result in greater speed differentials among vehicles in traffic, and might even increase the incidence of auto accidents. There is no question that excessive speed increases the severity of an accident, damage to the vehicles, and injuries to the occupants, however.

Although many people believe that reducing the speed limit will automatically reduce the speed of traffic, and increasing the speed limit will have the opposite effect, this is not necessarily the case. The 85th percentile speed, at which 85 percent of traffic flows, is widely accepted as the ideal speed limit, according to the Colorado Department of Transportation, although other things, such as road and weather conditions and traffic, also factor in. The Federal Highway Administration has created a Web-based software program, USLIMITS2, to help state and local agencies set appropriate speed limits.

Why Do Drivers Disregard Speed Limits?

Many drivers will ignore a speed limit that seems unrealistic and drive according to the perceived road conditions, but will obey a reasonable speed limit. Reasonable speed limits with appropriate signage have been found to reduce the speed difference between vehicles, in turn lowering the accident rate.

An appropriate speed limit will naturally result in most vehicles traveling at roughly the same speed, reducing speed differentials. In theory, a speed limit that is properly set will establish a middle ground for all drivers, encouraging some to speed up and others to slow down, and reduce the incidence of accidents under normal conditions.

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