Safety Evaluation of Horizontal Curve Realignment on Rural, Two-Lane Roads
The Federal Highway Administration established the Development of Crash Modification Factors (DCMF) program in 2012 to address highway safety research needs for evaluating new and innovative safety strategies (improvements) by developing reliable quantitative estimates of their effectiveness in reducing crashes. The ultimate goal of the DCMF program is to save lives by identifying new safety strategies that effectively reduce crashes and promote those strategies for nationwide implementation by providing measures of their safety effectiveness and benefit-cost (B/C) ratios through research. State transportation departments and other transportation agencies need to have objective measures for safety effectiveness and B/C ratios before investing in new strategies for statewide safety improvements. Forty State transportation departments provided technical feedback on safety improvements to the DCMF program and implemented new safety improvements to facilitate evaluations. These States are members of the Evaluation of Low-Cost Safety Improvements-Pooled Fund Study, which functions under the DCMF program. This study evaluated the effectiveness of horizontal curve realignment on rural, two-lane roads. One objective of this strategy is to reduce lane departure crashes, especially run-off-road crashes.
This evaluation developed crash modification factors (CMFs) for curve realignment on rural, two-lane roads using state-of-the-art before–after empirical Bayes methods and compared the results with previously developed CMFs from cross-sectional studies. The data included 39 realigned locations from California, North Carolina, and Ohio, and 56 untreated reference curves.
In addition to developing the CMFs through a before-after evaluation, this study also compared the total crash CMFs with the results from previous cross-sectional studies. The CMFs derived through this before–after evaluation are lower compared to CMFs estimated by two previous cross-sectional studies. The economic analysis revealed a B/C 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.