Evaluation of reverse curves focusing on the lateral friction demand on four-lane divided highways

Abstract

Horizontal curves on mountainous roads are highly crash-prone and geometric consistency is vital in their design. The drivers' lateral friction demand will be significantly affected if there are a substantial number of successive horizontal curves on these roads due to design limitations. This study is aimed to evaluate the safety of reverse curves using the lateral friction demand as a design criterion. Using a UAV, the required data were collected from ten reverse curves on a mountain highway in Iran for a multiple linear regression model to investigate the effects of geometric variables and speed of vehicles on the average lateral friction demand (f_d,mean). According to the results: (1) the length of the common tangent and the ratio of the curves’ radii affect f_d,mean, (2) the road longitudinal grade and the vehicle speed have positive effects on f_d,mean, but the curve superelevation affects it negatively and (3) when the length of the common tangent is ≈ 400 m and the curves’ radii are close, the vehicle trajectories are close to the expected trajectory based on the design. These results can help reverse curves to be designed more safely.