Horizontal curve realignment reduced crashes on rural two-lane roads

What the study found: Horizontal curve realignment on rural two-lane roads was associated with lower crash rates, including fewer total crashes, injury and fatal crashes, run-off-road and fixed object crashes, dark crashes, and wet crashes.
Why the authors say this matters: The authors conclude that the findings help evaluate the safety effectiveness of curve realignment, a strategy intended to reduce lane departure crashes, especially run-off-road crashes.
What the researchers tested: The study estimated crash modification factors, or CMFs, for curve realignment using a before-after empirical Bayes method and compared them with CMFs from earlier cross-sectional studies. It used rural two-lane road data from California, North Carolina, and Ohio.
What worked and what didn't: The evaluation found statistically significant reductions of 68% in total crashes, 74% in injury and fatal crashes, 78% in run-off-road and fixed object crashes, 42% in dark crashes, and 80% in wet crashes. The before-after CMFs were lower than those from two previous cross-sectional studies, and the economic analysis gave a benefit-cost ratio of 3.17:1.
What to keep in mind: The abstract says the results apply to a specific range of site characteristics, especially before-and-after curve degree, and the treated sites had a limited range of traffic volumes and segment lengths. The authors also note a need for further research with a larger sample of sites to assess the reliability of the CMFs.

Key points

• Curve realignment on rural two-lane roads was linked with fewer total crashes and fewer crash types related to injuries, fixed objects, darkness, and wet conditions.
• The study used a before-after empirical Bayes method to estimate crash modification factors, or CMFs.
• Statistically significant reductions included 68% fewer total crashes and 74% fewer injury and fatal crashes.
• The before-after CMFs were lower than those from two previous cross-sectional studies.
• The economic analysis reported a benefit-cost ratio of 3.17:1.