EXAMINING THE EFFECT OF GEOMETRIC DESIGN FEATURES ON THE SPEED IN HORIZONTAL CURVE ON MOUNTAIN ROAD

In this study, the effect of five geometric design features, including radius, superelevation, longitudinal grade, lane and shoulder width, on the average speed in the horizontal curve on a two-lane undivided rural road was investigated. The standardized regression coefficients showed that the most important factor affecting the speed was the radius (10.47) followed by the longitudinal grade (4.46). Superelevation and lane width had little effect. Shoulder width had no significant effect. This would be due to the wide width of the lanes. It was found that the relationships between speed and radius, longitudinal grade, superelevation and lane width were radical, quadratic, linear and linear, respectively. Increasing the longitudinal grade has increased the speed of the drivers. Increasing the superelevation was effective when its value changed from negative to positive.