Evaluating new treatments for improving driver performance on combined horizontal and crest vertical curves on two-lane rural roads: A driving simulator study

Combined horizontal and crest vertical curves are among the most hazardous road segments because of drivers’ difficulties in perceiving early road geometry. This study evaluates new treatments to improve the safety of horizontal and crest vertical curves and compares their efficiency for driver performance based on design consistency criteria under free flow traffic and on-coming traffic. A combination of chevron signs with three promising treatments included herringbones, sealed shoulder and a yellow blinking signal was applied to hazardous curve sections in a driving simulator. Performance measures consisted of mean of speed and lateral position. The results indicated that combining chevrons and a warning blinking signal is the most appropriate treatment for horizontal and crest vertical curves, as this resulted in lower speed and lateral position. In addition, speed and lateral position variations along the curves were lower compared to other treatments specially, with an on-coming vehicle. Sealed shoulder makes drivers drive faster while entering a curve and brake suddenly while changing direction. Using herring bones is found to reduce speed and speed differential along the curve but not lateral position which was even higher in treated curves particularly, in presence of an on-coming vehicle.