Radius requirements for reverse horizontal curves on three-dimensional alignments

Horizontal reverse curves are used in all types of highways either in mainline alignments or in freeway interchange ramps. At present, minimum radius requirements for reverse curves are determined based on vehicle performance on each are of the reverse curve individually without giving any consideration to the nature of the reverse curvature. This paper determines the required minimum radius for reverse curves on freeway mainlines based on vehicle stability using computer software to simulate truck behavior on different alignments. It was found that an increase to the minimum radius requirements of horizontal reverse curves is required to maintain the driver comfort levels suggested by design guides and to prevent potential rollover. That increase ranges from 8.3 to 28.8% depending on the geometric configuration of the highway as well as on the design vehicle. The design guidelines developed for horizontal reverse curves should be useful in improving road safety on highways, especially for freeway interchanges.