Safety Evaluation of Installing Center Two-Way Left-Turn Lanes on Two-Lane Roads

Abstract

FHWA organized a pooled fund study of 26 states to evaluate low-cost safety strategies as part of its strategic highway safety effort. One of the strategies chosen to be evaluated for this study was the installation of center two-way left-turn lanes (TWLTLs) on two-lane roads. Geometric, traffic, and crash data were obtained for 78 sites (21.3 mi) in North Carolina, 10 sites (6.0 mi) in Illinois, 31 sites (6.8 mi) in California, and 25 sites (13.2 mi) in Arkansas. Empirical Bayes methods were incorporated in a before–after analysis to determine the safety effectiveness of installing the TWLTLs. There was a statistically significant reduction in total and rear-end crashes in each of four states whose installations were evaluated. Rural installations were found to be more effective in reducing crashes than were urban installations in each of the four states. The general conclusion of this research is that TWLTLs can be a cost-effective treatment for two-lane rural locations, especially those with a high frequency of rear-end collisions involving a lead vehicle desiring to make a left turn.

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