Safety Effectiveness of Intersection Left- and Right-Turn Lanes

Abstract

The results of research involving a well-designed before-and-after evaluation of the safety effects of providing left- and right-turn lanes for at-grade intersections are presented. Geometric design, traffic control, traffic volume, and traffic accident data were gathered for a total of 280 improved intersections as well as 300 similar intersections that were not improved during the study period. The types of improvement projects evaluated included installation of added left-turn lanes, added right-turn lanes, and extension of the length of existing left- or right-turn lanes. An observational before-and-after evaluation of these projects was performed by using several alternative evaluation approaches. Three contrasting approaches to before-and-after evaluation were used: the yoked comparison or matched-pair approach, the comparison group approach, and the empirical Bayes approach. The research not only evaluated the safety effectiveness of left- and right-turn lane improvements but also compared the performances of these three alternative approaches in making such evaluations. The research developed quantitative safety effectiveness measures for installation design improvements involving added left-turn lanes and added right-turn lanes. The research concluded that the empirical Bayes method provides the most accurate and reliable results. Further use of this method is recommended.

Influence of built environment on pedestrian crashes: A network-based GIS analysis

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The Comparison Study on Observational Before-After Studies: Case Study on Safety Evaluation on Highways

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Estimation of Safety Effectiveness of Composite Shoulders on Rural Two-Lane Highways

“…Harwood et al documented that there are three common ways to carry out a before-after study: naï ve before-after evaluations, comparison group evaluations, and the EB approach (20). Of these three evaluations listed, the EB approach was widely recommended in the HSM (1).…”

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