Abstract
This study was initiated as a result of numerous skidding accidents occurring at locations where highway geometric include a combination of downgrade, a curve, and a super-elevation. Mathematical equations are developed for obtaining all the wheel forces (both normal and lateral) of a vehicle negotiating such a curve at the instant of incipient skidding for a variety of parameters. Factors which appear to be most important in regard to critical skidding velocities are the lateral coefficient of friction between the tire and the road surface, and driver manoeuvring. Factors which appear to have little influence are superelevation(if relatively small), cross wind velocity, and type of vehicle (excluding tractor-trailers).