Exploring maximum and minimum operating speed positions on road geometric elements using continuous speed data

Abstract

Speed prediction models are commonly developed using maximum and minimum operating speeds measured at or within specific locations on the tangents and horizontal curves, respectively. However, the actual distribution of the maximum and minimum operating speed positions on the entire lengths of the geometric elements (tangents and curves) have not been rigorously studied and, therefore, present opportunities to refine further and develop robust speed prediction models. This paper presents the probability distributions (normal, lognormal, gamma, and Weibull) for speed positions on the entire tangent and curve lengths using continuous speed data recorded on two-lane rural highways in India. The findings showed that the data could be best approximated for a large number of horizontal curves and tangents using the normal and Weibull distributions. Also, the results showed that the operating speeds measured at the midpoint of the horizontal curves overestimate the actual minimum operating speeds measured over the entire curve length of horizontal curves between 1.2 and 1.9 km/h. Similarly, maximum operating speeds measured at or within a 200-m length from the point of curvature into the approach tangents underestimate the maximum operating speeds measured over the entire length of tangents between 1.33 and 1.77 km/h. The results of this study highlight the importance of considering the entire length of geometric elements in developing accurate speed prediction models for use in evaluating highway design consistency.