MINIMUM HORIZONTAL CURVE RADIUS AS FUNCTION OF GRADE INCURRED BY VEHICLE MOTION IN DRIVING MODE

An enriched "bicycle" model was developed to describe the driving mode during the motion of a passenger car. The bicycle model is contrary to the mass-point model, which is suitable for the examination of the braking mode of a passenger car. The analysis concludes that there is a strong relationship between the radius of the horizontal curve and grade, which is found by studying vehicle motion on a helical surface. In some cases values of the minimum radius of the horizontal curve derived from the relationship exceed those suggested by AASHTO (1990) or RAS (1984). This means that, in such cases, existing guidelines lead to underdesigned values, because they do not consider that the driving mode during vehicle motion is critical.