National measures to curb speeding on local roads and interstate highways have proved to be largely ineffective. In fact, the federal government repealed the national speed limit in 1995, prompting some states to raise their limit as high as 85 mph. Despite all the technology to increase automobile safety and measures to make roads safer, speeding contributes to around one third of the 10,000 traffic fatalities each year, according to A 1998 study estimated the annual economic cost associated with deaths, injuries and damage from speeding was $27.7 billion.

The U.S. Department of Transportation provides guidance to state and local entities to ensure that posted speed limits balance the efficient movement of traffic with the elimination of unnecessary risks. As part of the analysis, unreasonable speed for the conditions significantly increases the risk of an auto accident and the chances of death or serious physical injury in that accident.

An Australian study found that in a 60 kilometer (approximately 37 miles) per hour zone, the chance of a crash involving death or serious injury is twice as likely by driving 65 km (approximately 40 miles) per hour. The risk increases exponentially with each mile per hour above that.

There are several reasons why even slight decreases in speed significantly reduce the risk of serious accident. Higher speeds reduce the time a driver has to react and attempt to avoid a collision. At high speeds and short distances, every second and every extra foot counts. This is particularly true for rear-end collisions where traffic may be at a complete stop and swerving may not be an option.

A shorter available reaction time will result in a higher impact speed due to less time braking. A higher impact speed increases the chances of serious injuries as more energy is transferred from one car to the other. Several tons of metal flying 70 to 80 mph is certainly a potentially deadly weapon, even if the other vehicle is well made.

Obeying posted speed limits is crucial to reducing the risk of accident. The limit takes into account expert opinion regarding road conditions and traffic volume and should be strictly heeded. Since studies show that exceeding the speed limit by even just a few miles per hour can double the risk of an accident, abiding by the limit will keep everyone on the road that much safer.