Study Details

Study Title: Another look at the safety effects of horizontal curvature on rural two-lane highways

Authors: Saleem and Persaud

Publication Date:SEP, 2017

Abstract: 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. The data for this study came from the Washington State database in the Highway Safety Information System (HSIS). Crash prediction models are developed for curve sections on rural 2-lane highway and the tangent sections up- and down-stream of the curve sections. Different negative binomial models were developed for segments on level grades (< 3%), moderate grades (3–6%), and steep grades (> 6%) to account for the confounding effects of gradient. The relationships between crashes at different traffic volumes and deflection angles are explored to illustrate how to get estimates of CMFs for increases in the minimum radius, considering the effect of increased tangent length for sharper curves, an effect that is overlooked in the Highway Safety Manual CMF, in addition to the effect of gradient. The results of that exploration indicated that even at different design speeds and deflection angles, the CMF estimates for incremental increases in radius lie within the same range, and that the crash reduction rate (CRR) is higher at segments on higher grades compared to the ones on lower grades.

Study Citation: Saleem, T. and B. Persaud. " Another look at the safety effects of horizontal curvature on rural two-lane highways". Accident Analysis and Prevention, Vol. 106, (2017) pp. 149-159.

Related Citations: Saleem, T. and B. Persaud., Another Look at the Safety Effects of Horizontal Curvature on Rural Two-Lane Highways. Presented at the 95th Annual Meeting of the Transportation Research Board, Washington, D.C., (2016).


CMFs Associated With This Study

Category: Alignment

Countermeasure: Flatten horizontal curve

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equation4 StarsAllAllNot specifiedRural
CMF Equation4 StarsAllK,A,B,CNot specifiedRural
CMF Equation3 StarsAllONot specifiedRural
CMF Equation3 StarsAllAllNot specifiedRural
CMF Equation3 StarsAllK,A,B,CNot specifiedRural
CMF Equation3 StarsAllONot specifiedRural
CMF Equation3 StarsAllAllNot specifiedRural
CMF Equation3 StarsAllK,A,B,CNot specifiedRural
CMF Equation3 StarsAllONot specifiedRural