Speed Behavior Analysis at Curved Ramp Sections of Minor Interchanges

Abstract

On and off ramps act as interfaces between freeways and the surface street network (nonfreeway highways) and in effect should provide a smooth and safe transition from one facility to another. The speed behavior of passenger cars at minor-interchange on and off ramps with unusual curved arrangements is analyzed in depth for the first time. Vehicle speed data were collected at 20 on and off ramps in Greece that have a variety of geometric features. Regression analyses were applied to investigate the variables affecting operating speed— V85. The best models resulted in coefficients of determination of nearly 0.75, indicating that operating speed is influenced by curvature change rate and superelevation rate. Comparison of the “Greek speed profile” with those of Australia, Austria, Germany, South Africa, and the United States proved that for on and off ramps it very closely approximates the values of Australia, Austria, and Germany. Austria is the only country using V85 to determine ramp geometrics. The differences between the Greek V85 and the speed values recommended by the German guidelines are considered small, ranging from 6 to 9 km/h for on ramps and −1.5 up to −4 km/h for off ramps. The analysis produced regression models that will provide designers with a tool to estimate the operating speed during the design process.