Speed Variability on Rural Two-Lane Highways

Abstract

A better understanding of speed variance on rural two-lane highways may assist in addressing driver error associated with highway geometric elements. Previous research has identified a direct relationship between speed variance and accident potential. Speed variance increases are associated with an increase in accidents. Therefore, identifying relationships between speed distribution measures of free-flowing vehicles and roadway characteristics may identify inconsistent roadway features. Horizontal and vertical curves from four geographic regions were identified based on selected criteria, and speed data were collected at the midpoint of the preceding tangent and the curve. Four hypotheses were explored to determine if relationships between speed statistics and geometry could be used to identify design inconsistencies. Statistical tests were conducted to identify relationships between mean speed, speed variance (standard deviation), and roadway characteristics for tangents, horizontal curves, and vertical curves. The findings suggest that speed distribution measures do not appear to be useful in the evaluation of design consistency.