U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
NCHRP Report 500 / Volume 12: A Guide for Reducing Collisions at Signalized Intersections
Signalized intersections with a high frequency of crashes related to drivers either being unaware of (or refusing to obey) traffic laws and regulations that impact traffic safety.
Telltale lights assist police officers by allowing them to sit downstream of the traffic signal and know when the red indication is displayed.
Photo by: FHWA
Enforcement is a potential countermeasure to unsafe and illegal motorist behavior at intersections. Studies report the reduction of traffic law violations when enforcement is used. Traffic law enforcement agencies will often select locations for targeted enforcement when crash, citation, or other sources of information suggest that the site is unusually hazardous due to illegal driving practices, such as speeding or red-light running. These actions can lead to rear-end, head-on, sideswipe, angle, and pedestrian- or bicycle-related crashes.
Traffic law enforcement methods vary depending upon the type of program being implemented. For background on methods and approaches, refer to the publications available on the National Highway Traffic Safety Administration website (http://www.nhtsa.dot.gov/people/injury/enforce/).
It is important to correctly identify intersections that would benefit from enforcement. Care should be taken to first ensure that the existing signals are operating properly, are visible, and meet Manual on Uniform Traffic Control Devices requirements, as well as that timing plans-including clearance intervals-are appropriate. Analysis of crash statistics can help with this process, as can spot speed or conflict studies. In some cases, public input or observations by law enforcement personnel may suggest that a location should be targeted for enforcement.
Police officers providing targeted enforcement of red-light running can be aided by "telltale" or "tattle-tale" lights. These lights are placed at traffic signals but face away from oncoming traffic. Police officers are able to wait in their vehicles on the downstream side of the traffic signal and view the tattle-tale light. This way, they are able to pursue red-light runners without also running through the red light themselves (and possibly into vehicles entering the intersection from the cross street).
Targeted enforcement can be implemented in a very short time.
Costs are low to moderate, depending upon the availability of law enforcement personnel.
TRIED: Targeted enforcement of traffic laws is a short-term, moderate-cost measure to address site-specific signalized intersection safety. Though this is an effective strategy, the effectiveness has often been found to be short lived. It is difficult—if not impossible—to provide constant enforcement of traffic regulations due to funding and staffing reasons, so periodic enforcement may be necessary to sustain the effectiveness of this strategy.
This strategy can be used in conjunction with the other strategies for improving safety at signalized intersections. It may be used in conjunction with overall traffic safety public service campaigns.
Targeted enforcement at intersections is also discussed in the Unsignalized Intersection Fact Sheet G1 and H1. A media specialist should be involved from the initial stage of project planning. Also refer to Countermeasures That Work from the National Highway Traffic Safety Administration.
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