Sometimes, the number of road traffic victims in a particular year is greater or less than was to be expected on the basis of normal statistical fluctuations. Such extreme fluctuations are often attributed to the influence of weather. This study attempts, in an explorative and descriptive way, to gain greater insight into the road safety effects of weather in the Netherlands. An attempt to quantify these effects is also initiated. It is examined if, and to what extent, extreme weather conditions are accompanied by important deviations in the numbers of victims, exposure, and (thus derived) victim rate. The data analysed are two-month periods between 1995 and 1998. The report produces clear indications that precipitation and temperature are the most important factors, when examining the relationship of weather and road safety in both summer and winter. A great amount of precipitation, as either rain or snow, generally accompanies a higher victim rate for all modes of transport, and a smaller exposure, especially for cyclists. During a mild winter and a warm summer, more kilometres are cycled. Also, in a mild winter with little precipitation, more kilometres are travelled by car. A warm summer is accompanied by a higher victim rate for car occupants. During the four years studied, the greatest weather influences occurred in 1995 and 1998. The study clearly shows that there is a measurable relation between, on the one hand the weather and, on the other hand the number of victims, the victim rate, and the exposure. The precipitation (rain and snow), the temperature, and the combination of the two should, therefore, be studied closer.
Abstract