Turn lanes are one of FHWA’s proven safety countermeasures for drivers. They are recommended to prevent collisions of vehicles turning left across opposing through traffic and to prevent rear-end collisions. However, a preliminary analysis of 2017–2024 crash data in Washington State indicated that there was a greater percentage of fatal and serious injury pedestrian collisions that occurred at intersections with left turn lanes and intersections with both right and left turn lanes compared to intersections with no turn lanes. It is not clear how this affects the overall safety of the intersection for all users in two very important ways. First, how do turn lanes affect the operating speed of the intersection and corridor in which the intersection is located? Second, how does the turning lane affect the likelihood of fatal and serious injuries of pedestrians and bicyclists?

Research is needed to investigate the tradeoff of the presence of turn lanes, recognizing that while they can improve network efficiency and isolate some conflicts, they may also eliminate a traffic calming feature that has a wider effect on the corridor speed and speed-related crashes. Additionally, there is a need to look at how a turn lane will affect the conspicuity of pedestrians/bicyclists, the predictability of movements of different user groups through the intersections, the effects of lengthening the crossing distance, conflict points, and the separation in space and time between motorists and pedestrians/bicyclists.

The objective of this research is to quantify and analyze the impacts of turn lanes on motorist operating speeds and pedestrian/bicyclist safety at intersections. More specifically, the research will focus on the following four aspects:

·       Investigate and evaluate the tradeoff of how turn lanes affect traffic safety and operations across all modes and understand the relationship between the presence of turn lanes and operating speed.

·       Evaluate circumstances where turn lanes may increase the risk for pedestrian and bicyclist fatalities or serious injuries.

·       Develop a crash modification factor (CMF) for removing turn lanes to potentially reduce pedestrian and bicyclist fatal/serious injury crashes. 

·       Determine alternative safety treatments that could utilize the space currently dedicated to turn lanes to improve the safety of the intersection for all users.