Rate of rotation, or 'warp factor' is a measure of the variation in crossfall of a road surface, and typically relates to a change in crossfall from that of a normal straight road to that chosen for a curve to enhance forces assisting a vehicle to stay on the road. The range of road geometries (crossfall, curvature, transition length and superelevation) typically found on the state highway network were determined, and the crash database interrogated to determine whether a critical rate-of-rotation limit corresponding to the onset of loss of control of vehicles could be established. On-road tests with instrumented vehicles were used to provide information on rates-of-rotation corresponding to occupant comfort and to provide calibration input to computer modelling. The computer modelling was used to establish rates-of-rotation resulting in loss of control for different vehicle types over ranges of road geometry and travel speed. Design criteria for rate of rotation were derived from this body of work from the perspectives of vehicle occupant comfort and safety.