U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
NCHRP Report 500 / Volume 5: A Guide for Addressing Unsignalized Intersection Collisions
Unsignalized intersections that are not clearly visible to approaching motorists, particularly approaching motorists on the major road. The strategy is particularly appropriate for intersections with patterns of rear-end, right-angle, or turning crashes related to lack of driver awareness of the presence of the intersection.
Photos by: FHWA
Many unsignalized intersections are not readily visible to approaching drivers, particularly drivers on major-road approaches that are not controlled by stop or yield signs. Thus, intersection crashes may occur because approaching drivers may be unaware of the presence of the intersection. The visibility of intersections and, thus, the ability of approaching drivers to perceive them can be enhanced by signing and delineation. Improvements may include advance guide signs, advance street name signs, warning signs, pavement markings, post-mounted delineators, and supplemental beacons on advance signs.
The FHWA Older Driver Highway Design Handbook encourages such improvements to contribute to a better driving environment for older drivers. In particular, the handbook addresses advance guide signs and letter height on guide signs as key issues for older drivers. Advance warning signs, such as the standard intersection warning sign, can also alert drivers to the presence of an intersection. Providing a break in pavement markings—including centerlines, lane lines, and edge lines—at intersections also helps to alert drivers to the presence of an intersection.
Select a combination of signing and delineation techniques appropriate to conditions on particular unsignalized intersection approaches. This engineering assessment should, where possible, be accompanied by a human factors assessment of signing and delineation needs. Also, the ability and commitment of the highway agency to adequately maintain the signing or delineation is important.
Care should be taken not to overuse traffic signing, which could result in drivers not perceiving the presence of intersections.
This strategy does not require a long development process. Signing and delineation improvements can typically be implemented in 3 months or less.
Costs to implement signing and delineation are relatively low. An agency's maintenance costs may increase.
TRIED: Making drivers aware that they are approaching an intersection, through the use of enhanced signing and delineation, should improve safety at the intersection because drivers will be more alert to potential vehicles on the cross streets. This heightened awareness will quicken drivers' reaction times when conflicts occur.
One study concluded that installing double stop signs can reduce all crashes up to 11% and right-angle crashes up to 55%. The same study concluded that installing advance warning signs can reduce all crashes up to 30% at urban locations and 40% at rural locations.
Another analysis indicated a crash reduction of 70% when flashing beacons were installed on advance of 3-leg intersections and up to 39% at 4-leg intersections.
This strategy can be used in conjunction with most other strategies for improving safety at unsignalized intersections.
Signing in conformance with the Manual on Uniform Traffic Control Devices should be provided.
For more details on this and other countermeasures: http://safety.transportation.org
For more information contact:
FHWA Office of Safety Design
E71, 1200 New Jersey Avenue SE
Washington, D.C. 20590
FHWA Resource Center – Safety and Design Team
19900 Governor's Drive, Suite 301
Olympia Fields, IL 60461