Study Details

Study Title: Developing Crash Modification Factors for Horizontal Curves on Rural Two-Lane Undivided Highways using a Cross-Sectional Study

Authors: Wu et al.

Publication Date:JAN, 2017

Abstract: Horizontal curves have been identified as experiencing more crashes than tangent sections on roadways, especially on rural two-lane highways. The first edition of the Highway Safety Manual (HSM) provides crash modification function (CM-Function) for curves on rural two-lane highways. The CM-Function proposed in the HSM may suffer from both outdated data and analysis technique. Before-after studies are usually the preferred method for estimating the safety effects of treatments. Unfortunately, this method is not feasible for curves. Previous studies have frequently used regression models for developing CM-Functions for horizontal curves. As recently documented in the literature, some potential problems exist with using regression models for developing crash modification factors (CMFs). This study utilized cross-sectional study to develop curvature CM-Function. Curves located on Texas rural two-lane undivided highways were divided into a number of bins based on the curve radius. The safety was predicted with the assumption that these curves had been tangents. The observed number of crashes that occurred on the curves was compared with the “dummy” tangents and for different bins. The results showed that horizontal curve radius has a significant role in the risk of a crash. Based on these results, a new CM-Function was developed. The prediction performance of the HSM CM-Function and another function that was recently proposed in the literature were compared 17 with the new CM-Function in this study. It was found that the new CM-Function documented in 18 this study outperformed both.

Study Citation: Wu, L., D. Lord, and S. Geedipally. "Developing Crash Modification Factors for Horizontal Curves on Rural Two-Lane Undivided Highways using a Cross-Sectional Study". Presented at the 96th Annual Meeting of the Transportation Research Board, Paper No. 17-02498, Washington, D.C., (2017).

Related Citations: Wu, L., D. Lord, and S. Geedipally. "Developing Crash Modification Factors for Horizontal Curves on Rural Two-Lane Undivided Highways using a Cross-Sectional Study". Transportation Research Record: Journal of the Transportation Research Board, No. 2636, 2017, pp. 53–61. http://dx.doi.org/10.3141/2636-07


CMFs Associated With This Study

Category: Alignment

Countermeasure: Change horizontal curve radius from straight tangent to radius of R feet

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equation3 StarsAllAllNot specifiedRural