COMPARISON OF DIFFERENT PROCEDURES FOR EVALUATING SPEED CONSISTENCY

Abstract

The need for achieving operating-speed consistency on two-lane rural highways through consistent horizontal alignment is discussed. One American and two European methods for evaluating horizontal alignment consistency are compared: a graphical speed-profile technique proposed for use in the United States, a theoretical speed model utilized by the Swiss highway design community, and a German procedure using a design parameter known as the curvature change rate. The results of the comparison of the three approaches show that although at times substantially different speed values are obtained from each method, the fundamental results necessary to evaluate alignment consistency are basically the same. On the basis of this comparison, it appears that the curvature-change-rate method is the most convenient for predicting changes in operating-speed profile along a rural roadway brought about by inconsistencies in horiaontal alignment.