Turner-Fairbank Highway Research Center

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Safety Evaluation of Horizontal Curve Realignment on Rural, Two-Lane Road

Product Type

Research Report


Raghavan Srinivasan, Daniel Carter, Craig Lyon, and Matthew Albee




The Development of Crash Modification Factors program conducted safety evaluation of horizontal curve realignment on rural, two-lane roads for the Evaluation of Low Cost Safety Improvements Pooled Fund Study. The goal of this evaluation is to evaluate the safety effectiveness of this strategy. This strategy sought to reduce lane departure crashes, especially run-off-road crashes. This study determined the crash modification factors (CMFs) associated with curve realignment using the before–after empirical Bayes method and compared the results from published CMFs from cross-sectional studies. This evaluation used data from rural, two-lane roads in California, North Carolina, and Ohio. The evaluation revealed a 68-percent reduction in total crashes, a 74-percent reduction in injury and fatal crashes, a 78-percent reduction in run-off-road and fixed object crashes, a 42-percent reduction in dark crashes, and an 80-percent reduction in wet crashes, all of which were statistically significant at the 95-percent confidence level. The results pertain to a range of site characteristics, the most important of which is the range of the before and after degree of curve. The average degrees of curve in the before and after periods were 18.1 (with a minimum of 3.2 and a maximum of 52.1) and 6.9 (with a minimum of 0.0 and a maximum of 16.3), respectively. The average central angle of the curves was approximately 42 degrees (with a minimum of 1 and a maximum of 117). The average annual average daily traffic at the treated sites was about 3,500 (with a minimum of 465 and a maximum of 11,917). The average length of the realigned segments was 0.15 mi (with a minimum of 0.03 and a maximum of 0.60). This study compared the total crash CMFs with the results from previous cross-sectional studies. The CMFs from this before–after evaluation are lower compared to CMFs estimated from two previous cross-sectional studies. The economic analysis revealed a benefit–cost ratio of 3.17:1 with a range of 1.75:1 to 4.38:1. There is a need for further research with a larger sample of sites to assess the reliability of the CMFs obtained from this before–after evaluation.

Link To Research Report

Safety Evaluation of Horizontal Curve Realignment on Rural, Two-Lane Road


Horizontal curve
rural two-lane roads
degree of curve
lane departure crashes
safety improvements
safety evaluations
empirical Bayesian
crash modification factors
crash modification functions
cross-sectional studies

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