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FHWA Home / Safety / Intersection / Red-Signal Enforcement Lights

Red-Signal Enforcement Lights

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May 2009


Red-Signal Enforcement Lights enhance safety at signalized intersections by improving red-light compliance, resulting in a reduction of red-light running violations. They are auxiliary lights connected to a traffic-control signal to help law enforcement officers more efficiently and safely issue citations for drivers who violate the red phase of the signal. According to the US Department of Transportation's Fatality Analysis Reporting System (FARS), 869 people were killed in crashes that involved red-light running in 2006, and the National Campaign to Stop Red-Light Running estimates that another 143,000 were injured.

Alternative Names

Red light indicator lights, red light indicators, signal indicator lights, enforcement lights, white enforcement lights, rat lights or boxes, tattletale lights.

This summary is one in a series describing Innovative Intersection Safety Treatments. The summaries identify new technologies and techniques to improve intersection safety developed since NCHRP Report 500, Volumes 5 and 12, were published in 2003 and 2004, respectively. These treatments show promise for improving safety but comprehensive effectiveness evaluations are not yet available.


The Red-Signal Enforcement Light activates simultaneously with the red signal phase, providing an enforcement officer located downstream from an intersection with a visible indication of the upstream red phase so they can determine when a vehicle has violated the red phase. Relatively small, low-cost lights are mounted on the top, bottom, or rear of a traffic signal and are wired into the signal controller for accurate red-signal phase indication. Red-Signal Enforcement Lights should not be colored red, yellow, or green, in order to avoid confusion with traffic signal control indications.

Potential Benefits

Red-Signal Enforcement Lights can provide safety, efficiency and/or cost benefits, compared to other enforcement methods. These benefits include:

Figure 1: Bottom-mounted Red-Signal Enforcement Light on a signal head.
Figure 2: Red-Signal Enforcement Light mounted at the top of a post-mounted signal head.

Agency Experience

Implementation Considerations


Learn More

Peter Hsu, Florida Department of Transportation

Jeffery Smith, San Jose Traffic Enforcement Unit

Ed Rice, Intersection Safety Team Leader
FHWA Office of Safety

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Page last modified on September 4, 2014
Safe Roads for a Safer Future - Investment in roadway safety saves lives
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