Vehicle Swept-Path and Driver Behavior at Sharp Curve Sections

When comparing traffic accidents on tangent and curving road sections, it is four times higher for curved sections compared to tangential sections. Therefore, the design of horizontal curves is crucial to the geometric design. Curve widening should be provided to facilitate the space needed to turn the vehicle in sharp bends. Computer-Aided Design (CAD) simulation software is used to model these vehicle turning trajectories to identify the actual swept path of turning vehicles. But there will be considerable deviations in real driving behavior, which leads to traffic accidents. Furthermore, driving behavior on hairpin curves are as ambiguous as different real-world driving patterns. Therefore, more studies are required to reach a better design and guidelines for hair-pin bends with higher safety. This research therefore studies the patterns of vehicle trajectories by using naturalistic driving data from Sri Lankan roads with low traffic volumes.

Determine whether there is any deviation between a real vehicle path and a model vehicle path generated by software, and if so, how much deviation is there and what guidelines should be implemented for road safety and geometric designs.

The behaviour of 5 types of vehicles at 6 different hair-pin bend locations at A26 road in Sri Lanka was studied by using drone camera videos. Vehicle type and dimension, vehicle speed, curve radius and deflection angle and road gradient (whether uphill or downhill) are considered as the factors affecting the trajectory variations. Lateral trajectory density distribution for each type of vehicle were drawn and compared with the optimum vehicles swept-paths generated using a computer aided design software. 

There is a visible deviation between a real vehicle path and a model vehicle path generated by software especially in the mid location of the hair-pin curve. Also, uphill and downhill behavior movements show that the gradient of the road affects the real driving behavior. 

Some modifications in hair-pin curves are needed such as widening at entrance and exit locations of the curve to facilitate slow and smooth turning behavior along the increased curve length of the hair-pin curve.