Length requirements for single-arc asymmetrical sag vertical curve for highways

Abstract

This paper presents the length requirements for a single-arc asymmetrical vertical curve (sag type) for highways that complements two other papers on the curve development and the length requirements (crest type) that have been published. The single-arc, asymmetrical curve takes the form of a cubic instead of parabolic function and its rate of change in grade gradually varies between the start and the end of the curve. The paper presents the length requirements of the single-arc asymmetrical curve based on the headlight, comfort, and overpass criteria. For the headlight criterion, sight distance (SD) relationships are first developed for the new curve considering different locations of the driver and object. The SD profile and minimum sight distance are then examined. Design aids are then established. The results show that the length requirements based on the comfort criteria are about 60% of those of the headlight criteria. The new single-arc asymmetrical curve improves curve characteristics, and as such would be of interest to the highway design community.