Turner-Fairbank Highway Research Center

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

Product Type

Research Report


Persaud, B., C. Lyon, K.A. Eccles, N.X. Lefler, D.L. Carter, and R. Amjadi




The Federal Highway Administration 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 on two-lane roads. This strategy is intended to reduce the frequency of crashes involving a turning vehicle, which could be classified as head on or rear end. Geometric, traffic, and crash data were obtained for 78 sites (34.9 km (21.3 mi)) in North Carolina, 10 sites (9.7 km (6.0 mi)) in Illinois, 31 sites (10.95 km (6.8 mi)) in California, and 25 sites (21.25 km (13.2 mi)) in Arkansas. Empirical Bayes methods were incorporated in a before-after analysis to determine the safety effectiveness of installing the two-way left-turn lanes. 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 urban ones in each of the four States. Lower cost installations of 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 turn.

Link To Research Report

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


highway safety
two way left turn lanes
two lane highways
highway design
rear end collisions
head on collisions
before and after studies
evaluation and assessment

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