1. Highway traffic count on the national highways;ASTRA,1995
2. A study of the causal connection between accident occurrence and skid resistance;Hirsche,1990
3. Requirements for the skid resistance of pavement surfaces — skid resistance and traffic safety;Kamplade;Strasse und Autobahn,1995
4. Skid resistance of pavement surfaces;Mayer,1990
5. Relation of accidents and pavement friction on rural, two-lane-roads;Rizenbergs,1977