road manager
How To Make Street and Road Intersections Safer
We faced nearly three million intersection-related
crashes last year, or about 44% of all reported road accidents. Specific
steps can help cut this number.
by Ruth W. Stidger,
Editor-in-Chief
There were about 8,500 fatalities at intersections, or 23% of all road
accident deaths, and about a million injury crashes.
New ways to improve intersection safety include:
1. Use of best practices for selection, design and installation,
operation, and maintenance of traffic control devices.
2. Improved geometric design and lighting of intersections.
3. Use of crash data to identify crash-prone locations that need work.
4. Upgraded signal phasing, timing, and coordination to smooth traffic
flow.
5. Use of intelligent controllers and detectors, as well as audible
pedestrian signals.
6. Use of techniques combined with access management policies.
 These and
other goals were set out by James A. Bonneson, as associate research
engineer at the Texas Transportation Institute. Bonneson presented
engineering solutions, as well as goals, at last November’s Intersection
Safety Workshop held in Milwaukee.
The problems
Intersection safety isn’t the cut-and-dried engineering solution
situation it might seem. Human nature plays a large and
difficult-to-control role.
 In a study
of why roadway accidents happen, Elizabeth Alicandri says that reasons for
crashes overlap. Driver factors are involved in 93% of crashes. Roadway
aspects are included in 34% of the accidents. Vehicle malfunctions can be
included in 12% of crashes.
People hurry, speeding to work or appointments. Many are distracted by
tasks or personal pressures, by cell phones, or by kids fighting in the
back seat. Some take out their frustrations on their driving, feeling
powerful and secure inside their vehicles.
Key driver intersection maneuver errors include:
1. Overestimating the yellow signal time remaining.
2. Underestimating the time needed to reach an intersection.
3. Underestimating the time needed to make a smooth stop.
4. Underestimating the time needed to accelerate to speed after making
a turn.
Over half of driver errors at intersections are decision-making
related, says Alicandri, who works in the Safety Core Business Unit of the
Federal Highway Administration.
Intersection visibility — including signage, signage contrast, the
driver’s color vision, intersection complexity, and visual illusions —
affects driver performance, too.
Design and location
Some intersection design and location factors lead to more crashes than
others.
In an eight-state study completed for the University of North Carolina
Highway Safety Research Center, most fatal intersection accidents —
about 85% — happen at junctions with no signals.
A little less than 75% of these were multiple-vehicle accidents, and
most resulted from one or more drivers making a turn.
Left turns were found to be particularly dangerous, and were involved
in 46.7% of fatal intersection crashes. Right turns were involved only
2.3% of the time.
Two-way stop intersections were the most dangerous at four-leg
intersections on rural roads, while similar urban intersections had
markedly fewer fatal crashes in most of the states studied.
Placing signals at intersections cut crashes by as much as 10 to one,
the study shows.
Engineering solutions
It’s easier to engineer intersection solutions when new roads are
being built. When designing for intersections without signals, separate
traffic movements with bays, says Bonneson, at the Texas Transportation
Institute. Be sure intersection details will be visible at a distance.
For intersections with signals, modify the curb-corner radius design to
make turns (especially left turns) easier and more visible to other
drivers.
Add pedestrian refuge islands.
Be sure to include traffic control in new or updated intersection
designs. Use flashing beacons at rural intersections, Bonneson recommends.
Use intersection lighting, especially where no signals will be placed.
In signalized intersections, add marked crosswalks and a protected
left-turn phase.
Signs as solutions
Proper signage helps with both intersection design and human response.
Sign size is important. Make sure drivers can easily see both Stop
Ahead and Stop signs or electronic signals.
Be sure trees and shrubs don’t hide the signs you place.
Pavement markings and delineation should lead the driver through the
intersection safely. Lane bays and turning lanes should be marked with
reflective materials. Striping must be visible even in heavy rain and
other adverse weather conditions.
Place signs and signals for maximum visibility.
Sign colors, placement, and other factors must follow guidelines set
out in the new edition of the FHWA’s Manual of Uniform Traffic Control
Devices.
Driver attention
Drivers need help from highway engineers when they approach
intersections. They need to:
1. Maintain speed. Agencies can help by setting signal timing
correctly.
2. Maintain lateral position. Lane and turning-lane markings help most.
3. Be aware of surveillance. Red-light-running cameras, long used in
Europe, have become an increasingly popular way to keep drivers from
speeding up when they see yellow signals and from running red lights.
4. Pay attention. Optimum signal placement can help turn driver
attention from in-car distractions to the road.
5. Determine lane for down-road maneuvers. Advanced signage helps guide
the driver who wants to turn, find a specific adjoining route, or be sure
of continuing through the roadway.
6. Enter the correct lane. Overhead signs, combined with lane markings,
work well.
7. Decelerate for a stop. Advance signage can help, especially at busy
urban intersections where signals often compete with commercial signs and
buildings.
8. Reinforce or obtain information about regulations. Signs, including
permanent Intelligent Transportation Systems with changeable message
boards, can help inform drivers about intersections and related problems
such as rush-hour congestion.
9. Adjust speed in anticipation of a signal. Warning signs, such as
Stop Ahead help the most with this task.
10. Search for path guidance. Medians, striped lanes, and or turn
lanes, plus good signage, keep drivers on the correct path.
Funding
Increased sign and marking use, as well as other intersection devices,
mean spending more money.
Where to find that funding is a focal point of the preliminary draft of
the National Agenda for Intersection Safety, which was developed during
the National Intersection Safety Workshop.
Key strategies for programs and legislation recommended by workshop
participants include:
1. Actively promote increased safety funding in reauthorization.
2. Create safety program funds for use by local governments.
3. Make the current program more helpful at the local level.
4. Take 3% of the highway funds in a given year and use them for safety
purposes.
5. Seek legislation that provides for 100% obligation of safety
set-aside funds.
6. Implement best practices by providing incentives to states and local
governments.
7. Tie funding to accountability and demonstration of results. Federal
safety funds would be tied to performance standards.
8. Provide funding for safety evaluation training for engineers and
technicians.
9. Develop a clearinghouse for intersection safety.
10. Seek legislation that provides dedicated funding for automated
crash reporting.
Other recommendations
Workshop participants want a systems approach to intersection safety.
This includes setting up permanent partnerships between law enforcement,
education, and road engineering organizations and professionals.
More research is needed, especially in driver information
countermeasures costs and benefits of intersection safety steps, and
intersection collision avoidance technology.
Better information will help, and the Federal Highway Administration is
providing training for road-safety audit reviews to all state departments
of transportation.
Setting traffic signals with appropriate — usually longer — yellow
clearance times was recommended. Use of red-light-running cameras and
other increased enforcement were also supported.
Better training to help professionals design safer intersections is a
major need, workshop participants say. Online courses, such as those from
the Institute of Traffic Engineers, can be used.
Roundabouts, used in Europe, can help avoid the stop-start dangers of
some intersections, letting drivers enter an intersection and circle until
they can safely exit.
Photos courtesy of AASHTO and Caltrans.
When drivers don’t stop
Pierce County, Washington regularly conducts intersection traffic
safety studies, says James W. Ellison, P.E. These are based on reported
collision history, citizen concerns, and operational observations.
An increasingly common trend found in these studies has been drivers
failing to heed stop signs that clearly have adequate visibility. When
such a trend is identified, the county implements a progressive approach
using several steps:
1. Install Stop Ahead sign.
2. Increase size of Stop and Stop Ahead signs from 30 to 36 inches.
3. Install two transverse rumble button patterns in the approach lane
in advance of the Stop Ahead and before the Stop sign.
4. Consider installation of two additional transverse rumble button
patterns to supplement the first two locations.
5. Install overhead intersection flashing-red beacon with illumination;
consider also installing flashing-yellow indications on intersecting
through road.
What help’s available?
Several tools can help address the intersection safety problem.
The AASHTO Strategic Highway Safety Plan. The goal for this strategic
plan is to improve the country’s present and predicted statistics on
vehicular-related death and injury. The plan contains six main elements:
drivers, special users, vehicles, highways, emergency medical services,
and management; as well as 22 emphasis areas. The National Agenda for
Intersection Safety ties its strategies to specific AASHTO emphasis areas
to ensure coordination among various coalition partners. You can find plan
information at http://safetyplan.tamu.edu.
Project 17-18(3), FY 2000: Guidance for Implementation of the AASHTO
Strategic Highway Safety Plan. This research will develop guidance to help
state and local highway agencies with implementing strategies to reduce
fatalities by 10 to 15% in aggressive driving, head-on and
run-off-the-road crashes on two-lane roads, people who drive with
suspended and revoked licenses, hazardous trees that need to be handled in
an environmentally acceptable manner, and unsignalized intersections.
Information can be found on the Transportation Research Board’s Web
site, http://www4.trb.org/trb/crp.nsf.
Click on NCHRP, All Projects, and go to Area 17.
Outreach Toolkit. This kit lets policymakers have a
user-friendly way to communicate and elevate awareness and understanding
of intersection safety problems when speaking to the public. A set of
briefing sheets is under development. These will include facts, issues,
and potential solutions about various aspects of intersection safety.
Briefing sheets available this year include:
1. The National Intersection Safety Problem.
2. Red-Light Running.
3. Red-Light Cameras.
4. Basic Countermeasures to Enhance Intersection Safety.
5. What are Traffic Control Devices: Their Use and Misuse.
6. Intersection Safety Enforcement.
7. Safety of Pedestrians and Bicyclists in Intersections.
8. Human Factors Issues in Intersection Safety.
9. Intersection Safety Myths versus Reality.
10. Highway and Street Work-Zone
Intersection Safety Issues.
11. Intersection Safety Resources. The kit will be available on
both the FHWA and ITE Web sites.
Intersection Safety Video. This video, Red Light, Green Light,
will provide the traveling public and the transportation community with
increased awareness of the critical importance of intersection safety. The
video lets viewers identify steps they can take to improve their own
safety and also provides data on what the transportation professional is
doing to help create safer intersections. It will be available from ITE.
Infrastructure Intersection Collision Avoidance. The Federal
Highway Administration has partnered with the departments of
transportation in California, Minnesota, and Virginia to form an
infrastructure consortium. Their research effort includes analysis of
crashes and mitigation concepts, development of intersection
collision-avoidance concepts and algorithms, development of analytical
models to assess safety countermeasures, development of
infrastructure-based sensors, examination of human factor issues,
definition of vehicle infrastructure communication methods, assessment of
the benefits and cost as well as barriers to deployment, and development
of in-vehicle systems.
ITE Online Learning Gateway. The Institute of Traffic Engineers
has developed one course, in a series of courses to follow, on
transportation safety. TS02 Safety of Signalized Intersections was
developed as a guided tutorial approach to help transportation
professionals analyze crash data and identify appropriate countermeasures
to reduce the frequency of crashes and fatalities, person injury, and
property damage. The course can be accessed at www.ite.org.
What about roundabouts?
 The modern
roundabout is a circular intersection that features channelized
approaches, yield control for entering vehicles, and geometric curvatures
that ensure that travel speeds within the roundabout typically are 30
miles per hour or less. As of last September, Maryland had more than 25
modern roundabouts in operation along state-maintained highways. Eight of
these replaced conventional intersections for which before accident data
are available and they have been in operation long enough to obtain good
after accident data.
Maryland’s first eight roundabouts are small-to-moderate size (outer
inscribed circle diameter of 150 feet or less), with one circular lane and
single-lane entries. The average daily numbers of entering vehicles range
from 3,700 to 21,000 with most carrying 9,000 to 14,000 vehicles per day.
These roundabouts were mostly built as alternatives to installing
traffic signals being demanded by the public in response to real or
perceived accident-prone intersections. Signals were deemed unwarranted or
otherwise inappropriate. Each roundabout replaced stop signs or
intersection control beacons previously controlling the intersections.
 In spite of
traffic growth, since conversion to roundabouts, the annual accidents for
the eight intersections dropped from an average of 5.0 accidents per year
in the before period to an average of 1.8 accidents per year in the after
period, a 64% reduction.
Accident severity also decreased. Injury accidents were reduced from an
annual average of 3.0 before to 0.5 after, a reduction of 83%. Each of the
eight locations had a reduction in both total reported accidents and
injury accidents.
Reprinted from Better Roads Magazine
July 2002 |
