Chen Li, Chen Cynthia, Ewing Reid
City College of New York, United States.
University of Washington, Seattle, United States.
Accid Anal Prev. 2015 Mar;76:102-9. doi: 10.1016/j.aap.2014.12.019. Epub 2015 Jan 24.
The practice of left-turn phasing selection (permissive, protected-only, or both) varies from one locality to another. The literature evidence on this issue is equally mixed and insufficient. In this study, we evaluate the safety impacts of changing left-turn signal phasing from permissive to protected/permissive or protected-only at 68 intersections in New York City using a rigorous quasi-experimental design accompanied with regression modeling. Changes in police reported crashes including total crashes, multiple-vehicle crashes, left-turn crashes, pedestrian crashes and bicyclist crashes were compared between before period and after period for the treatment group and comparison group by means of negative binomial regression using a Generalized Estimating Equations (GEE) technique. Confounding factors such as the built environment characteristics that were not controlled in comparison group selection are accounted for by this approach. The results show that the change of permissive left-turn signal phasing to protected/permissive or protected-only signal phasing does not result in a significant reduction in intersection crashes. Though the protected-only signal phasing does reduce the left-turn crashes and pedestrian crashes, this reduction was offset by a possible increase in over-taking crashes. These results suggest that left-turn phasing should not be treated as a universal solution that is always better than the permissive control for left-turn vehicles. The selection and implementation of left-turn signal phasing needs to be done carefully, considering potential trade-offs between safety and delay, and many other factors such as geometry, traffic flows and operations.
左转相位选择的做法（允许、仅保护或两者皆有）因地区而异。关于这个问题的文献证据同样参差不齐且不充分。在本研究中，我们使用严格的准实验设计并结合回归模型，评估了纽约市68个十字路口将左转信号相位从允许变为保护/允许或仅保护的安全影响。通过使用广义估计方程（GEE）技术的负二项回归，比较了治疗组和对照组在前期和后期警方报告的撞车事故变化，包括总撞车事故、多车撞车事故、左转撞车事故、行人撞车事故和骑自行车者撞车事故。这种方法考虑了在对照组选择中未控制的混杂因素，如建成环境特征。结果表明，将允许的左转信号相位改为保护/允许或仅保护的信号相位并不会导致十字路口撞车事故显著减少。虽然仅保护的信号相位确实减少了左转撞车事故和行人撞车事故，但这种减少被超车撞车事故可能增加所抵消。这些结果表明，左转相位不应被视为一种普遍优于左转车辆允许控制的解决方案。左转信号相位的选择和实施需要谨慎进行，要考虑安全与延误之间的潜在权衡，以及许多其他因素，如几何形状、交通流量和运营情况。
