January/February 2003
Reducing Points of Conflict
by Joe G. Bared, Patrick Hasson, Fred N. Ranck,
Hari Kalla, Robert A. Ferlis, and Michael S. Griffith
FHWA targets intersection safety.
An intersection is, at its core, a planned point of conflict in the
highway system. Crashes related to these points of conflict in the
United States resulted in almost 9,000 fatalities and about 1.5 million
injuries in 2001 alone. These incidents represented 44 percent of
all reported crashes in the Nation, or a staggering 2.8 million.
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Violent intersection crashes such as this one between an
SUV and a concrete delivery truck are all too common and exact
a high toll.
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Clearly, intersection safety is a critical component of overall highway
safety. Moreover, because of the nature of the safety problem at intersections,
solutions often require committed and coordinated action on the part
of a variety of traditional and nontraditional partners.
Transportation and safety organizations throughout the country, as
well as enforcement agencies, traffic engineers, and public education
and outreach groups—either government officials or local citizen
groups—must work together to make a substantive difference in
the reduction of intersection-related crashes. And they are.
The Federal Highway Administration (FHWA) identified safety
as one of its Vital Few goals. As a means of focusing its safety efforts,
FHWA's strategic goal is to reduce the number of highway-related fatalities
and injuries by 20 percent by 2008. Additionally, FHWA also established
the objective of reducing intersection fatalities 10 percent by 2007.
To this end, FHWA and a number of other highway organizations are
orchestrating a variety of innovative activities and research initiatives.
From informational guidebooks to research programs and international
scans, FHWA and its partners are working to improve intersection safety
through the design of smarter roundabouts and signalized intersections,
reduced red light running, and other cutting-edge research to increase
the safety of America's road users.
New Tool for Roundabouts
Research indicates that well-designed roundabouts with single-lane
and double-lane entries, where conditions are appropriate, can be
safer and more efficient than conventional intersections. Indeed,
injury and fatal crashes can be reduced 20 percent for traffic flows
of double-lane roundabouts with approximately 40,000 average daily
traffic (ADT), and by as much as 70 percent for traffic flows of single-lane
roundabouts up to 20,000 ADT. Roundabouts also mean less delay to
motorists as opposed to conventional stop- or signal-controlled intersections.
A key intersection treatment tool by FHWA's Intersections Research
program is its report, Roundabouts: An Informational Guide
(2000). The guide provides comprehensive educational and prescriptive
information, covering all aspects related to roundabouts: from policy
considerations to planning, traffic analysis, geometric design, traffic
control devices, and special applications. The guide is widely used
as a primary reference and authority on the subject.
Speed and Path Choice for Roundabouts
FHWA's Human Centered Systems (HCS) Team in Safety Research and Development
is examining the influence of geometry and lane delineation on motorists'
choice of speed and path in double-lane roundabouts. By conducting
field studies on two Maryland double-lane roundabouts, the research
team aims to provide additional information on the speed imposed on
motorists by geometric design. The results will be used to update
the geometric design of roundabouts. The update will augment bicyclist
and pedestrian safety at roundabouts, including individuals with disabilities.
In the Maryland study, vehicles are being observed through cameras
mounted high above the intersections, to assess lane position and
speed for individual vehicles before they enter the roundabout, once
they are in it, and when they exit. In addition to the field tests,
HCS researchers in the laboratory are examining path and speed choices
of drivers. With simulated roundabouts, researchers can examine the
effects of two alternative roundabout entry geometries and markings,
without the need to build or modify a roundabout. To validate the
simulation method, the roundabouts observed in the field were replicated
in the simulator.
The results of both field and simulated research will be available
in the spring of 2003.
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Intersections like this one that have numerous driveways
in close proximity offer unique challenges to engineers and
special risks to users.
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Improving Roundabout Safety, Design, and Operation
Although modern roundabout design is relatively new to the United
States, perceived differences in motorists' behavior raise questions
about how appropriate some international research and practices are
for adoption in this country. Additional information on the safety
and operation of roundabouts in the United States is needed to help
planners and designers determine where roundabouts would reduce intersection
crashes and congestion, and how current design criteria could be improved.
To this end, FHWA is contributing to the Transportation Research
Board's (TRB) National Cooperative Highway Research Program's (NCHRP)
Project 3-65, Applying Roundabouts in the United States. This project
will develop methods of estimating the safety and operational impacts
of U.S. roundabouts and, ultimately, refine roundabout design criteria.
The NCHRP expects that the project will be completed in the summer
of 2005. For more information, please visit www4.nas.edu/trb/crp.nsf/NCHRP+projects
(click on Area 3).
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A roundabout in Golden, CO.
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Red Light-Running Guide
One of the primary causes of crashes at signalized intersections
occurs when motorists enter intersections when the red signal is displayed
and collide with other motorists, pedestrians, or bicyclists who are
legally within the intersection. According to the journal Accident
Analysis and Prevention, these red light-running crashes, which
occur approximately 200,000 times each year, have an alarmingly high
injury rate of 45 percent—significantly higher than the injury
rate for other crash types, which is 30 percent.
Red light running is a complex problem with no simple cause or solution.
Although driver error, such as distractions, inattention, and willful
disregard, as well as driver psychology and sociology, play a role
in explaining some violations, numerous reports and anecdotal evidence
suggest that engineering deficiencies also may be at fault. For example,
yellow change intervals can be set so low that they "trap" motorists
into running red lights. Similarly, intersections with limited sight
distance to the signals make it difficult for a motorist to see the
red signals in time to avoid running the red light.
To provide better guidance on the engineering features that contribute
to red light running, FHWA and the Institute of Transportation Engineers
(ITE) are working on a new guide, Making Intersections Safer: A
Toolbox of Engineering Countermeasures to Reduce Red Light-Running
Crashes. Intended for engineers, law enforcement, and other officials,
the guide provides a comprehensive background on the characteristics
of the red light-running problem, presents engineering measures that
can be implemented to solve it, and helps users select appropriate
engineering measures to meet the specific needs and conditions. The
guide will be publicly available in January 2003.
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When motorists disobey traffic control devices, as the tractor-trailer
drivers in this photo are doing they put themselves and others
in great danger.
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Improving Collision Prediction
Being able to predict potential driver behavior or traffic collisions
successfully is critical to improving safety on the road. But making
these predictions is easier said than done. Existing crash models
are contingent upon retrospective crash statistics, which may not
provide a large enough sample. Additionally, transportation engineers
may not have the right information to represent correctly specific
conditions on a road or at an intersection. Relying solely on crash
statistics for crash modeling can be costly in terms of both human
safety and infrastructure investment.
To enable safety engineers and roadway designers to work around these
limitations and better evaluate the safety and mobility of roadway
and intersection designs and treatments, FHWA is in the process of
developing safety measures from traffic simulation models that can
be complementary to actual crash data.
Specifically, FHWA researchers are identifying and defining appropriate
and measurable surrogate actions or events, and then evaluating the
applicability and capabilities of existing traffic simulation models.
Useful measures sought by FHWA include information on the expected
time for two vehicles to collide if they remain at their present speeds
and paths, and the time lapse between cars and the amount of space
necessary for changing lanes. Once surrogate measures are defined,
functional requirements and logic for simulation software that depicts
safety measures for intersections will be developed.
FHWA expects to complete the initial phase of the project by early
2003. The initial phase involves exploring surrogate safety measures
within simulation models, evaluating the capabilities of traffic simulation
models, identifying functional requirements, and developing a logic/algorithm
for a surrogate safety assessment methodology. Planning is now underway
for the second phase, which will include the promotion of a surrogate
safety assessment module, as well as validation and incorporation
of the safety measures into existing simulation software.
Signalized Intersections
FHWA is in the process of designing an informational guide for medium-
and high-volume signalized intersections. The goal is to synthesize
safety and operational characteristics by developing comprehensive
guidelines for all design and operational features for all highway
users. FHWA also intends to develop a research program for conventional
and innovative intersections, median U-turns, and displaced left-turn
lanes.
The guidelines, expected to be complete by the end of 2003, will
address all considerations related to signalized intersections comprehensively,
taking the reader step-by-step through the project development process,
legal considerations, user considerations, symptoms identification,
causal evaluation, treatments, implementation, and monitoring.
International Scan on Signalized Intersection Safety
To identify innovative safety practices in the planning, design,
operation, and maintenance of signalized intersections, in May 2002,
FHWA and the American Association of State Highway and Transportation
Officials (AASHTO) sponsored a European scan to Germany, the Netherlands,
Sweden, and the United Kingdom. The team included 13 representatives,
with members from FHWA, AASHTO, ITE, TRB, State departments of transportation
(DOTs), municipal transportation agencies, universities, and the private
sector. Members possessed diverse technical skills and expertise in
the planning, design, operation, and maintenance of signalized intersections.
Coordinated by FHWA's Office of International Programs, the scan
was designed to identify and evaluate promising and readily executable
solutions and programs for intersection safety that could be implemented
in the United States. Specifically, the scan targeted six major areas
of interest. The first was the selection, design, installation, operation,
and maintenance of traffic control devices at signalized intersections,
with a focus on the safety implications at each stage. Second and
third were innovative traffic control devices and geometric designs
for signalized intersections. The fourth focus was procedures for
problem identification, evaluation, and countermeasure selection at
signalized intersections with safety problems; fifth, low-cost safety
improvements for signalized intersections; and the final focus was
research projects focused on safety issues at signalized intersections.
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A signalized intersection at Tysons Corner, VA.
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The team met with national and municipal transportation administrations
and ministries, university faculties, research organizations, and
industry representatives in the four countries. They observed specific
safety improvements in the field and gathered information on site-specific
studies and examples of safety improvements. Through discussions and
site visits, the participants also identified potential barriers or
special needs regarding implementation of such strategies and programs
in the United States.
Key Findings
Based on the knowledge gained, the team developed a set of observations,
key findings, recommendations, and ideas for implementation. The European
countries share a number of common characteristics with respect to
intersection safety:
- One national agency is responsible for developing and maintaining
a national highway system.
- Each national organization provides safety guidance with different
target levels of crash reduction focused on fatalities and serious
injuries.
- Typically, specific intersection safety issues are identified,
studied, and corrected at the local level with support from national
and State agencies.
- Strong emphasis is placed on protecting the vulnerable road user
(pedestrians and bicycles).
- Safety concerns generally outweigh congestion and mobility issues.
- Shorter cycle lengths at signalized intersections are used to
improve pedestrian and bicycle operations.
- Automated photo enforcement is used to minimize unsafe driver
behavior at intersections (speeding and red light running).
- Vehicle detectors and signal controller software packages are
used to vary signal timings and address congestion and "dilemma
zone" issues. (The dilemma zone is the area where drivers find themselves
if, when they see the yellow indication, they lack adequate distance
to stop before the intersection but are too far away to enter the
intersection before the red indication.)
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Highway engineers struggle with a complex array of signals,
markings, and signs to make intersections, like this one in
the Netherlands, as simple for users to navigate as possible.
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According to Office of Safety Chief Highway Safety Engineer Rudy
Umbs, the team's preliminary recommendations include: (1) developing
a model photo enforcement process/program for implementation at signalized
intersections, (2) identifying and implementing demonstration projects
for enhanced dilemma zone detection, and (3) developing a pilot project
to control speed through intersections using a combination of practices
implemented in Europe. Formal recommendations will be included in
the final scan report scheduled for completion in spring 2003. The
team's final implementation strategy will be reflected in the Scan
Technology Implementation Plan (STIP).
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Cities in the United States and around the world must meet
the demand for movements of large numbers of people and vehicles
through the same space. This crowded intersection is a street
in London.
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Safety Effectiveness of Intersection Left-
and Right-Turn Lanes
Does adding a turn lane make intersections safer?
The answer is a resounding yes. But how much safer?
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Well-defined right-turn lanes, such as this one in
Sherman County, OR, improve the safety of motorists
entering intersections.
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A new FHWA TechBrief, "Safety Effectiveness of
Intersection Left- and Right-Turn Lanes," presents the results
of research on the safety effectiveness of providing left- and
right-turn lanes for at-grade intersections.
Researchers selected three types of sites for
the study from eight of the participating States: improved
or treatment sites, comparison sites, and reference
sites. The improved or treatment sites are intersections
at which a left- or right-turn lane was added and for which
data on intersection geometrics, traffic volumes, and traffic
accidents were available for time frames before and after the
improvement. For 260 of the 280 improved intersections, the
researchers selected a matching comparison site that was not
improved during the study period. In addition, they selected
40 reference sites, which were both unimproved and not matched
to any particular improved site.
The researchers collected traffic volume data
for both the major- and minor-road legs and evaluated traffic
accident records for all accidents within 75 meters (246 feet)
of each intersection that were related to the presence of the
intersection, as designated by the investigating officer or
accident coder.
In addition, results are presented in the report
for installing left-turn lanes on the major-road approaches
to rural intersections and installing right-turn lanes on the
major-road approaches to rural and urban intersections. In addition,
economic evaluations of the installation of left-turn lanes
at various types of intersections were conducted, thereby allowing
the calculation of benefit-cost ratios and cost-effectiveness
thresholds.
The full research report is available at www.tfhrc.gov/safety/safety.htm.
Michael S. Griffith
Expected Percentage Reduction in Total Accidents
for Installation of Left-Turn Lanes on Major-Road Approaches
to Urban Intersections |
Intersection Type
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Intersection Traffic
Control
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Number of Major-Road
Approaches
Where Left-Turn Lanes Are Installed
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|
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One Approach % Reduction
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Both Approaches % Reduction
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Three-Leg Intersection
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Stop sign
Traffic signal
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33
7
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Four-Leg Intersection
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Stop sign
Traffic signal
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27
10
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47
19
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Source: One of several tables in FHWA's TechBrief
FHWA-RD-02-103. |
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Guidelines for Intersection Partnerships
In cooperation with NCHRP's Project 17-18, FHWA is supporting AASHTO's
Strategic Highway Safety Plan. The focus of the plan is to
develop and validate guidance documents, and to assist State and local
agencies with reducing fatalities in targeted areas, including signalized
and unsignalized intersections.
Under this initiative, The Implementation Guidelines to Address
Unsignalized Intersections has been developed and validated by
selected State and local transportation agencies. The strategies addressed
in this guidebook include improving management of access near unsignalized
intersections; improving driver awareness of intersections as viewed
from the intersection approach; choosing appropriate intersection
traffic control to minimize crash frequency and severity; improving
driver compliance with traffic laws and control devices at intersections;
and reducing operating speeds at intersection approaches. This guidance
document will be available in early 2003 in hard copy from TRB and
electronically via http://www.transportation1.org/SafetyPlan/
and www.transportation.org.
To address signalized intersections, a draft compendium of strategies
for safety at signalized intersections was recently peer-reviewed
and is now being revised. Specific means for achieving geometric,
operational, and traffic control improvements are among the major
strategies recommended for reducing the frequency and severity of
intersection conflicts. Major strategies identified include improving
sight distance, driver awareness of intersections and signal control,
driver compliance with traffic control devices, and access management
near signalized intersections. NCHRP expects that the revised compendium
will be available by the end of 2003.
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A non-signalized T-intersection in rural Virginia.
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Safer Intersections Ahead
The federally designated pooled fund Infrastructure Consortium, made
up of several State departments of transportation, is working to develop
and deploy advanced highway safety technologies. The consortium's
initial focus is to develop infrastructure-based intersection collision
avoidance systems. Possible technologies include relatively complex
systems that could identify safety threats with traffic and pedestrian/bicycle
sensors, analyze traffic movements to determine appropriate means
to avoid the threat, and communicate the needed responses to drivers.
This communication could be infrastructure-only, such as the activation
of a strobe light when a driver is about to violate a stop sign, or
it could be vehicle-highway cooperative, such as messages inside vehicles
that warn drivers who are about to violate a traffic signal or alert
them to potential collisions with traffic signal violators. The Infrastructure
Consortium members are hopeful that infrastructure-based intersection
collision avoidance systems could be deployed as early as 2010. In
addition to its other efforts, FHWA is working on the development
of a comprehensive and crosscutting roadmap on intersections.
Although crashes, injuries, and fatalities at intersections are not
entirely avoidable, much can be done to improve the current situation.
Thanks to the innovative activities and cutting-edge research being
carried out by FHWA and its partners, American motorists, cyclists,
and pedestrians today and in the future can look forward to safer
intersections.
"Safety is a shared responsibility among engineers, law enforcement
officials, and highway users," notes Rudy Umbs. "Everybody must do
his or her part to save lives. Engineers must use the latest technology
and practices. Enforcement must ensure that laws are obeyed. Highway
users—motorists, bicyclists, and pedestrians—must be aware
of ever-changing conditions and act sensibly, courteously, and sanely."
Joe G. Bared is a highway research engineer in FHWA's Office
of Research and Development. He manages research contracts and conducts
staff research in the areas of safety and the operational effects
of design. He has a doctorate in transportation engineering from the
University of Maryland, and he is a registered professional engineer.
Patrick Hasson is the safety and operations team leader in
FHWA's Midwestern Resource Center. In this position, he is involved
in regional, national, and international projects in the areas of
geometric design, Intelligent Transportation Systems, and safety engineering,
education, and enforcement. He is the national coordinator for the
FHWA Stop Red Light Running Program and is actively involved in the
intersection safety programs. He holds a B.S. in engineering from
the University of Maryland and an M.S. in engineering from Cornell
University.
Fred N. Ranck is the safety/geometrics engineer for FHWA's
Safety Team of Excellence, providing technical support to the FHWA
Divisions and States across the country; member of FHWA's MUTCD team
with responsibility for Part 2; member of FHWA's Intersection Safety
Team and Work Zone Policy Team. He is a licensed professional traffic
operations engineer and professional engineer in Illinois. Ranck has
a B.A. in physics and a B.S. and M.S. in civil engineering from the
University of Illinois.
Hari Kalla is a transportation specialist for FHWA in Washington,
DC. He leads the intersection safety program area in FHWA's Office
of Safety. He received a master's degree in civil engineering from
State University of New York and is a registered professional engineer
in New York.
Robert A. Ferlis is a research engineer and team leader for
enabling technology in FHWA's Office of Operations Research and Development.
He has served as the crosscutting coordinator of the IVI Program since
1998, where he supports research in vehicle-highway cooperation and
currently is responsible for managing the IVI research in intersection
collision avoidance systems. He received a B.S. in systems engineering
from the University of Illinois and a masters in civil engineering
from Northwestern University.
Michael S. Griffith is the technical director of FHWA's Office
of Safety Research and Development. He chairs the committee for a
new FHWA study evaluating the safety effectiveness of red-light running
cameras. Griffith is also active in a number of national initiatives
such as the Research and Technology National Partnership Initiative
and the Highway Safety Manual.
Other Articles in this issue:
Saving Lives: A Vital FHWA Goal
Helping Research Pay Off
Safer Roadsides
Making Two-Lane Roads Safer
Driving After Dark
Reducing Points of Conflict
Life in the Crosswalk
Pushing through the Safety Plateau
Data is Key to Understanding and Improving Safety
Managing Speed