Design Options to Reduce the Turning Vehicle and Bicycle Crashes at Intersections
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.
The proposed research will develop guidelines for intersection design that
minimize the risk that motor-vehicle turning movements create for
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.
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,
[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.
[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.
When Do Drivers Yield to Cyclists at Unsignalized Roundabouts? Empirical
Evidence and Behavioral Analysis Ary P. Silvano, Xiaoliang Ma, and Haris N.
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
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.
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.
2--Survey of Practice of to identify the typical and innovative design treatments for bicyclists at
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.
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
· 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
· 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).
4 – Prepare an interim report documenting the literature review, the
survey of practice, potential data sources, and proposed work plans.
5—Execute Work Plan developed in Task
3 and approved by NCHRP panel.
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
|Sponsoring Committee:||AFB10, Geometric Design
|Research Period:||24 - 36 months|
|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.|
|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|
Pedestrians and Bicyclists
Operations and Traffic Management
Safety and Human Factors