Chances for a traffic accident increase with the speed of traffic, as does the chance of serious injury. It is however difficult to quantify exactly the influence of speed in the occurrence of traffic accidents. Rules of thumb trying to capture the relationship between speed and accidents in formulas are often of little use as important factors like type of road or differences in speed are ignored. SWOV is currently investigating the speed-accident relationship on roads with a speed limit of 80 km/hour in the Netherlands; later other types of road may be investigated as well.