Investigating the impact of precipitation on vehicle speeds on UK motorways

Climate change impact assessments require detailed information regarding the impact of weather in the current climate. This study focuses on the road network, using UK Highways Agency Traffic Information System data and NIMROD precipitation radar data to determine the impact of precipitation on traffic speeds along the M1 and M6 corridors for use in future impact assessments. The results show that whilst precipitation does impact on traffic speeds, there is no universal significant single factor relationship between the two variables and only a small amount of variance in traffic speeds can be explained by the intensity of precipitation. However, a threshold appears to exist simply at 0 mm h^-1 (i.e. precipitation/no precipitation). The significance of this threshold is tested in this paper, but it appears clear that a universal relationship between precipitation intensity and vehicle speeds is unlikely to exist and local conditions such as capacity and drainage are equally as important to take into account.