Speed is a central issue in road safety. In fact, speed is involved in all accidents: no speed, no accidents. Speed has been found to be a major contributory factor in around 10% of all accidents and in around 30% of the fatal accidents. Both excess speed (exceeding the posted speed limit) and inappropriate speed (faster than the prevailing conditions allow) are important accident causation factors. In addition, speed generally has a negative effect on the environment, but a positive effect on travel time. The negative effects are mainly a societal problem and are hardly noticed by individual drivers; individual drivers on the other hand, particularly notice the positive effects.