Reducing Conflicts Between Bicycles and Turning Motor Vehicles
One of the most common locations for fatal motor vehicle–bicyclist crashes is at intersections. A newly published report offers guidance for improving intersection safety, especially in situations where a bike is traveling straight through an intersection and a car is turning across the cyclist's path.
The objective of the study was to develop guidelines and tools for transportation practitioners to reduce and manage conflicts between bicyclists and drivers turning at signalized intersections.
"Reducing Conflicts Between Turning Motor Vehicles and Bicycles: Decision Tool and Design Guidelines" was funded by the National Cooperative Highway Research Program (NCHRP), a program of the National Academies of Sciences, Engineering, and Medicine. The research was led by Toole Design in partnership with Portland State University (PSU), Safe Streets Research and Consulting (SS) and Oregon State University (OSU). The PSU team members were Chris Monsere, Sirisha Kothuri and Jason Anderson of the Maseeh College of Engineering and Computer Science, and Nathan McNeil of the Transportation Research and Education Center (TREC).
WHAT DID THE RESEARCHERS STUDY?
The research team conducted crash analysis, video-based conflict analysis, and a human factors study to better understand the effects of known common risk factors. These known risk factors include vehicle volume, vehicle speed, and bicyclist volumes. They also evaluated the relative safety performance of five different intersection treatments:
- Conventional bike lane at intersection,
- Separated bike lane at intersection,
- Pocket bike lane,
- Mixing zone, and
- Protected corner.
While there are many other types of intersection treatments available, such as bike boxes, two-way separated bike lanes or shared-use paths, these five were selected for study based on critical knowledge gaps identified through a review of the existing research.
WHAT DID THEY LEARN?
Based on the safety analysis, the researchers concluded the following for each intersection treatment:
Separated bike lanes and protected corners at intersections are the preferred treatments, with leading interval or full-phase signal separation in some conditions.
Conventional bike lanes at intersections are only recommended once practitioners have made every effort to reallocate space to provide a protected corner or a separated bicycle lane.
Pocket bike lanes are only recommended in limited situations.
Mixing zones are only recommended if right-turning motor vehicle volumes are high and practitioners have made every effort to reallocate space to provide a right-turn lane and a separated bicycle lane at the intersection.
HOW WILL THIS HELP IMPROVE SAFETY AT INTERSECTIONS?
The decision tool and supplemental design guidelines shared in this report provide an expanded framework for practitioners to assess trade-offs between various intersection treatments, and guidance to help them make decisions to manage conflicts between bicyclists and right-turning motorists.
The Decision Tool
The tool, illustrated here as a flowchart, provides guidelines related to urban, suburban, and rural town center land-use contexts. It focuses on the primary risk factors most likely to affect safety outcomes for bicyclists.
The Design Guidelines
In a set of supplemental design guidelines, the researchers provide recommendations for mitigating known safety concerns for each intersection treatment. The fourth chapter of the report includes comprehensive detail and discussion of each treatment.
These guidelines incorporate the safety performance of treatments, while considering bicyclists’ perceived comfort, which can affect if and where people will ride bikes.
In order to effectively apply the decision tool and the guidelines, practitioners should have an understanding of several key concepts, including the Safe Systems Approach, which are discussed in detail in the chapter on Decision-Making Principles.
This report stands as a valuable resource for transportation practitioners who are seeking evidence-based guidance on how to create safer intersections.
Portland State University's Transportation Research and Education Center (TREC) is a multidisciplinary hub for all things transportation. We are home to the Initiative for Bicycle and Pedestrian Innovation (IBPI), the data programs PORTAL and BikePed Portal, the Better Block PSU program, and PSU's membership in PacTrans, the Pacific Northwest Transportation Consortium. Our continuing goal is to produce impactful research and tools for transportation decision makers, expand the diversity and capacity of the workforce, and engage students and professionals through education, seminars, and participation in research. To get updates about what's happening at TREC, sign up for our monthly newsletter or follow us at the links below.
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