Another Look at the Safety Effects of Horizontal Curvature on Rural Two-Lane Highways

Crash Modification Factors (CMFs) are used to represent the effects on crashes of changes to highway design elements and are usually obtained from observational studies based on reported crashes. The design element of interest for this paper is horizontal curvature on rural 2-lane highways. Crash prediction models are developed for curve sections on rural 2-lane highway and the tangent up and down stream of the curve sections and their predictive capabilities are evaluated. The relationship between crashes at different traffic volumes and deflection angles are explored to get approximate estimates of CMFs for increases in the minimum radius (by factors of 1.10, 1.25, 1.50, and 2.00) considering the effects of increased tangent lengths for sharper curves. The overall results indicate that even at different design speeds and deflection angles, the CMF estimates for incremental increases in radius lie within the same range.