Geographical distribution of road slipperiness in Sweden, on national, regional and county scales

The influence of latitude on the distribution of slipperiness of roads in Sweden was studied at three scales: national, regional and county. Data from 654 Road Weather Information System (RWIS) stations were compiled over five winter seasons, from 1998/1999 to 2002/2003. The aim of the study was to establish a basis on which to model how future climate changes might affect frequency of slipperiness and costs for maintenance in winter. Four types of slipperiness were studied (slippery conditions due to moderate (HR1) or severe (HR2) hoarfrost, moist/wet surface that freezes (HT), and rain or sleet falling on a cold road (HN)), all adding up to form the winter index (WI). In Sweden, the distribution of slipperiness varies depending on the scale (national, regional or county). On the national and regional scales the mean temperatures give a general picture of the total slipperiness—i.e. dependence on latitude; different factors were tested and latitude proved to be the most correlated. Slipperiness caused by HR1 and HR2 hoarfrost tends to increase towards the north, while road icing (HT) decreases. On the county scale, neither latitude nor any other tested geographical variable, could explain much of the variance. Local climate and the directions of movement of individual weather systems may be more important. The regional scale is considered to be most suitable for future modelling of the influence of the effect of a changed climate on the slipperiness of the roads. Copyright © 2007 Royal Meteorological Society