Relationship to Safety of Geometric Design Consistency Measures for Rural Two-Lane Highways

The relationship of safety to five candidate measures of geometric design consistency for rural two-lane highway alignments was examined. The measures that were evaluated included: ( a) speed reduction on a horizontal curve relative to the preceding tangent or curve, ( b) average radius, ( c) ratio of maximum radius to minimum radius, ( d) average rate of vertical curvature, and ( e) ratio of individual curve radius to average radius. All of these measures were found to have statistically significant relationships to accident frequency in the direction expected and are recommended as candidate measures for assessment of geometric design consistency. The relationships between design consistency measures and accident frequency were developed using Poisson, negative binomial, and lognormal regression analysis.