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 (fd,mean). According to the results: (1) the length of the common tangent and the ratio of the curves’ radii affect fd,mean, (2) the road longitudinal grade and the vehicle speed have positive effects on fd,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.

Keywords

• Reverse curves
• Lateral friction demand
• Driver comfort
• Vehicle trajectory
• Mountainous highway