Model for Predicting Speed Along Horizontal Curves on Two-Lane Highways

This paper describes the development and calibration of a curve speed prediction model. The model includes variables for curve radius, deflection angle, superelevation rate, and tangent speed. The model is based on the hypothesis that drivers modify their side friction demand because of a desire for both safe and efficient travel. One model component reflects a general desire by motorists to have lower side friction demand on higher speed curves. This trend likely reflects the driver's desire to maintain an acceptable margin of safety against sliding out or rolling over. A second model component reflects a willingness by drivers to tolerate slightly higher side friction demand on sharper curves in an effort to minimize the amount of speed reduction. The increase in side friction demand that a driver accepts is found to be proportional to the energy required to slow the vehicle to the curve speed.