Effect of Horizontal Curve Geometry on the Maximum Speed Reduction: A Driving Simulator-Based Study

Operating speed reduction models can be used to evaluate the geometric design consistency. The proposed study developed a maximum speed reduction model for drivers habituated in weak lane disciplined driving conditions. The required experiment was carried out on a fixed-base driving simulator. The speed profiles of 48 participating drivers along 24 different tangent-curve configurations were recorded. The maximum speed at the preceding tangent and the minimum speed in the following curve were used to estimate the maximum speed reduction (MSR) of each subject driver. A multiple regression model was developed for the obtained 85th percentile maximum speed reduction data and the road geometric parameters such as radius, curvature, preceding tangent length, curve length, gradient, shoulder width, and extra-widening. The developed model identified curvature (i.e., the inverse of radius) and preceding tangent length as predictor variables. Based on the obtained results, a nomogram for road geometric safety evaluation is proposed in the paper.