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 with patterns of right-angle crashes related to lack of driver awareness of the presence of the intersection. In particular, it might be appropriate to use this strategy at the first stop-controlled approach (possibly of a series) located on a long stretch of highway without any required stops, or at an intersection located after a sharp horizontal curve.
Photo by: Texas Transportation Institute
Many stop signs at stop-controlled intersections are not readily visible to approaching drivers due to geometric conditions, presence of vegetation, or other objects (such as tall vehicles) that can limit the view of the regular stop signs. Thus, intersection crashes may occur because approaching drivers may be unaware of the presence of the stop sign at the intersection. The visibility of stop signs and, thus, the ability of approaching drivers to perceive them, can be enhanced by providing supplementary stop signs suspended over the roadway.
The target for this strategy should be stop signs at intersections that are not clearly visible to approaching motorists, particularly approaching motorists on the minor road. The strategy is particularly appropriate for intersections with patterns of rear-end, right-angle, or turning collisions related to lack of driver awareness of the presence of the intersection or stop sign.
Locate the supplementary overhead sign (or signs) in the direct line of sight of approaching drivers.
Unless the signs are mounted on existing overhead structures (mast arms), additional hardware will have to be placed on the roadside, which could become an additional object that a vehicle may strike if it leaves the roadway.
This strategy does not require a long development process and can typically be implemented in 3 months or less.
The costs involved in providing supplementary overhead stop signs are minimal when the signs are mounted on existing structures. The additional cost of providing a mast arm is moderate. Agencies may experience additional maintenance costs.
TRIED: The safety effectiveness of providing supplementary stop signs mounted over the roadway has not been quantified.
This strategy can be used in conjunction with most other strategies for improving safety at unsignalized intersections.
Supplementary signs should be in accordance with the MUTCD.
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