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Design Options to Reduce the Turning Vehicle and Bicycle Crashes at Intersections

Description:

Each year, vehicle-bicycle collisions result in hundreds of cyclist deaths and many more non-fatal injuries (the exact numbers are difficult to define due to lack of consistent reporting methods). In some cities, the most common location for these collisions is at intersections, which inherently have a large number of turning conflicts. For example, over 89% of fatal bicycle crashes reported in New York City during 2005 occurred at or within 25 feet of intersections. As a result, improving bicycle facilities at intersections has become a critical safety topic. Reducing these crashes is a key objective in improving intersection safety across all modes. Of particular concern for bicyclist safety at intersections are the conflicts between straight-through bicyclists and motor vehicle right-turns and opposing left-turns. Despite the widespread acknowledgement of this problem, transportation engineers and planners still lack definitive guidance on how to safely and effectively design for bicycles at intersections in the United States. Thus, research on effective methods to reduce these conflicts, with accompanying intersection design guidance, is a high priority.

The primary guidance documents for practitioners, including the AASHTO Guide for the Development of Bicycle Facilities and the NACTO Urban Bikeway Design Guide, are often based on professional judgment rather than research. Often, current design practices drop bicycle pavement markings and signs at intersections, providing no positioning guidance for motorists or bicyclists. Given the high levels of conflicts and crashes at intersections, it is not clear that this is the most effective approach. Alternatively, some US jurisdictions’ customary design continues bicycle lane markings all the way through to intersections; in others, the lanes are dashed. Moreover, innovative treatments including bike boxes, use of color, bicycle signals, and separated crossings are being implemented across the country. Some of these have been examined through research studies, and have so far demonstrated promising results, but the results are not conclusive.

There is no comprehensive research to indicate what design provides the most effective approach or the most appropriate situation in which each should be applied. Intersections should be carefully designed to enhance safety, improve operational efficiency, accommodate bicycle travel, minimize conflicts, and reduce the danger that turning cars pose to bicycle through-movements. Research on alternative designs to reduce conflicts at intersections is required to determine best practices to meet these objectives.

Objective:

The proposed research will develop guidelines for intersection design that minimize the risk that motor-vehicle turning movements create for through-moving bicyclists

Benefits:

This project will add a great value to researchers and practitioners concerned with the intersection operations and safety. The design and operation guidelines providing safer interactions between bicyclists and vehicles could be immediately implemented in new roadway, reconstruction, and resurfacing projects related to the design of urban intersections. The results of this project could help the traffic engineers in implementing the new and improved designs for reducing the conflicts and potential for crashes at intersections, and increase operational efficiency. Improved intersection design features are likely to be easy and inexpensive to implement in new designs, and may have significant safety benefits.

The research results and finding of this project could also provide an added value to AASHTO Green Book and the 2nd edition of the Highway Safety Manual.

Related Research:

Studies show that intersections with bicycle-specific treatments can help decrease bicycle-related crashes in conflict zones ([i],[ii],[iii]). These treatments can improve visibility and slow traffic, which can help to reduce the number of crashes involving vulnerable road users and/or reduce the injury severity of such crashes. Moreover, unlike most of the roadway improvements that target vehicle crashes, the improvements for preventing bicyclist crashes are very cost effective. For example, a study by Portland State University estimated that adding a bicycle lane could cost as little as $1-5 per foot ([iv]).

In addition to the potential to improve safety, bicycle facilities also encourage road users to bicycle as a means of transportation, which may reduce congestion, improve air quality, and improve health outcomes. While improved bicycle infrastructure can be a factor for crash reductions, driver speed and bicyclist lane positioning are key factors for a higher driver yielding rate ([v]). For example, on longer road segments and near intersections, bicycle crashes have been found to be significantly more likely to be fatal when they involve motorists traveling straight, occur along roadways between intersections, and involve motorists traveling in the same direction as the bicyclist ([vi], [vii]). As more facilities are installed, particularly newer facilities like separated bike lanes, there is an increasing need to evaluate the safety impacts and design guidelines for these facilities to ensure that the most appropriate facilities are built for the context and the identified safety problems ([viii]).


[i]. Brady, John, “Operational and Safety Implications of Three Experimental Bicycle Safety Devices in Austin”, presented at 90th Annual Meeting of the Transportation Research Board, Washington, DC, 2011.

[ii]. Enhancing Cycling Safety at Signalized Intersections Analysis of Observed Behavior Jeffrey M. Casello, Adam Fraser, Alex Mereu, and Pedram Fard Transportation Research Record: Journal of the Transportation Research Board, No. 2662, 2017, pp. 59–66. http://dx.doi.org/10.3141/2662-07

[iii]. Loskorn, Jeff, “Effects of Bicycle Boxes on Bicyclist and Motorist Behavior at Intersections in Austin, Texas”, presented at 90th Annual Meeting of the Transportation Research Board, Washington, DC, 2011.

[iv] Weigand et al. (2013) Cost Analyssi of Bicycle Facilities: Cases from Cities in the Portland OR Region. OR: Portland State University.

[v]. When Do Drivers Yield to Cyclists at Unsignalized Roundabouts? Empirical Evidence and Behavioral Analysis Ary P. Silvano, Xiaoliang Ma, and Haris N. Koutsopoulos https://doi.org/10.3141/2520-04

[vi]. Enhancing Cycling Safety at Signalized Intersections Analysis of Observed Behavior Jeffrey M. Casello, Adam Fraser, Alex Mereu, and Pedram Fard Transportation Research Record: Journal of the Transportation Research Board, No. 2662, 2017, pp. 59–66. http://dx.doi.org/10.3141/2662-07.

[vii]. Level-of-Service Model for Protected Bike Lanes Nick Foster, Christopher M. Monsere, Jennifer Dill, and Kelly Clifton Transportation Research Record: Journal of the Transportation Research Board, No. 2520, Transportation Research Board, Washington, D.C., 2015, pp. 90–99. DOI: 10.3141/2520-11

[viii]. User Behavior and Perceptions at Intersections with Turning and Mixing Zones on Protected Bike Lanes Christopher M. Monsere, Nick Foster, Jennifer Dill, and Nathan McNeil Transportation Research Record: Journal of the Transportation Research Board, No. 2520, Transportation Research Board, Washington, D.C., 2015, pp. 112–122. DOI: 10.3141/2520-13.

Tasks:

Task 1 – Review of the Literature on the estimated impact of various speed measures on crash likelihood and severity, such as average or 85th percentile, speed variance, speed compliance and other identified measures. Report the estimates, sample sizes, and the speed measures being evaluated.

Task 2--Survey of Practice of to identify the typical and innovative design treatments for bicyclists at signalized intersections.

Task 3 – Prepare a detailed work plan for the safety effectiveness evaluation of the existing intersections treatments. The work plan shall include

o Identify prevalent motor vehicle/bicycle crash types at signalized intersections.

o Identify the existing data sources (collected through field studies or crowdsourced data) to evaluate safety (both for bicycles and vehicles) at intersections with some or all of the following treatments:

· Exclusive turn lanes

· Colored pavement for bike travel paths through intersections

· Separate stop bar locations for motor vehicles and bicycles

· Bike boxes

· Alternative methods to accommodate bicycle left-turns (e.g. through bike lanes)

· Bicycle signal-heads with accompanying bicycle specific signal phasing

· Protected intersections (also known as Dutch junctions)

· Other relevant pavement markings, signs, and signal designs (e.g. sharrows, marked/dashed bike lane/bike travel path through intersections).

o Upon identification and selection of appropriate candidate intersections, evaluate intersection safety and develop Crash Modification Factors (CMFs).

Task 4 – Prepare an interim report documenting the literature review, the survey of practice, potential data sources, and proposed work plans.

Task 5—Execute Work Plan developed in Task 3 and approved by NCHRP panel.

Task 6 – Prepare final deliverables documenting the safety impacts of various design treatments for the intersections, as well as the geometric design properties of the selected treatments.

Task 7 – Develop Guidelines summarizing the research results in a practitioner’s guide for effective accommodation of bicycles at intersections. A key outcome of this research is the ability to determine those intersection designs that provide the most effective means of improving bicycle safety for specific situations/environments.

Sponsoring Committee:AFB10, Geometric Design
Research Period:24 - 36 months
Research Priority:Medium
RNS Developer:Krista Nordback -- University of North Carolina, Rebecca Sanders -- Arizona State University, Bahar Dadashova -- Texas A&M Transportation Institute, Rachel Carpenter -- Caltrans, Marcus Brewer -- Texas A&M Transportation Institute
Source Info:Developed by the Bicycle Research Subcommittee of the TRB Committee on Bicycle Transportation (ANF20) in conjunction with the Committees on Geometric Design (AFB10), Operational Effects of Geometrics (AHB65), and Highway Safety Performance (ANB25), along with the TRB Intersections Joint Subcommittee.
Date Posted:02/18/2019
Date Modified:02/26/2019
Index Terms:Highway design, Bicycle crashes, Turning traffic, Intersections, Highway safety, Traffic safety,
Cosponsoring Committees:ANF20, Bicycle Transportation; AHB65, Operational Effects of Geometrics; ANB25, Highway Safety Performance
 
Subjects    
Highways
Pedestrians and Bicyclists
Design
Operations and Traffic Management
Safety and Human Factors

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