An Analysis of Relationships between Running Behavior of Vehicles and Road Alignment at a Black Spot S-shaped Curve on a Motorway

Abstract

This paper describes a study involving a constant-speed run survey by plural drivers at an S-shaped expressway curve section where accidents have frequently occurred. The right-turn curve that is the first half of the section successively comprises the first clothoid curve, the first circular curve, the second clothoid curve, and the second circular curve. We estimated each run to fall into an understeering state because the lateral acceleration did not increase despite an increase in steering angles from the end of the first circular curve. Those observations matched the run trajectories estimated by the GPS positioning, likely caused by the discontinuous re-increase in curvature at the end. Based on video data framed by plural cameras, we estimated run trajectories of unspecified vehicles’ lateral acceleration of a run at 125 km/h to reach around 2.5 m/s². The lateral acceleration was close to an upper limit on wet road surfaces, potentially resulting in uncontrollable situations when combined with the understeering states.