Relationships between road slipperiness, traffic accident risk and winter road maintenance activity

A method for deriving quantitative relationships between road slipperiness, traffic accident risk and winter road maintenance (WRM) activity is descri bed. The method is also applied to data from an area in southern Sweden. If a specific type of road slipperiness represents a large accident risk desp ite high WRM activity it is important to increase public awareness during s uch periods. If the type of slipperiness represents a large accident risk b ut is accompanied by low WRM activity, it is also important to increase the WRM to reduce the accident risk. In the method, a road slipperiness classi fication, based on atmospheric processes, is used to classify the road cond itions at the time an accident occurred. The road condition is classified e ither as non-slippery or as one out of 10 types of slipperiness. Data for t he slipperiness classification are taken from the Swedish Road Weather Info rmation System (RWIS). Results from this study show that the traffic accide nt risk was different for different types of road slipperiness. Highest acc ident risk was associated with road slipperiness due to rain or sleet on a frozen road surface. When accidents occurred in these situations, there was always high WRM activity. This indicates that, in order to reduce the acci dent rate during these situations, public awareness must be increased by pr oviding information to drivers. The study also demonstrates the benefits of applying a standardized road slipperiness classification to all kinds of s ources of road safety information, such as a RWIS, traffic accident reports and WRM reports. With a standardized and objective classification of the r oad conditions and digitally stored data, all evaluations are easily conduc ted.