Road widening is necessary in curves because the rear wheels of the vehicle are usually not steerable and their trajectory is described with a smaller radius than that of the front wheels. The maximum value of the road widening depends on the turning angle, the radius of the curve and the length of the vehicle, the wheelbase and the front overhang. The required road widening increases gradually with a higher turning angle and decreases gradually as the vehicle leaves the curve and continues in the direction. This paper presents the determination of road widening in curves according to the Croatian regulations, German guidelines and computer simulation of the vehicle movement. The road widening determined according to the above mentioned guidelines and regulations for certain design vehicles (truck with trailer, semi-trailer truck and bus), different radii of circular curves (from 12.5 to 500 m) and different turning angles (from 45 to 270°) is compared with the road widening determined by computer simulation of vehicle movement with the Autodesk software Vehicle Tracking.

road widening, curve radius, turning angle, design vehicles, vehicle movement geometry