U.S. flag

An official website of the United States government, Department of Justice.

Evaluation of traffic behavior in response to alternative police lighting

NCJ Number
Accident Analysis and Prevention Volume: 144 Dated: 2020
Date Published

This study examined various types of lighting on police vehicles to determine whether changes made to the visibility of a police vehicle can impact the surrounding traffic behavior and increase safety for both law enforcement and the general public. 


Unmarked and marked police vehicles were positioned behind a civilian vehicle on the shoulder of five different multi-lane highways in Virginia, simulating a routine traffic stop. The data collected indicated that more lighting and the use of red in a light bar impact traffic behavior in terms of merging and speed when passing a police vehicle. The benefits may be attributed to the symbolic influence of red as denoting a different type of emergency than a traffic stop in addition to red’s chromatic contrast against the blue sky during the daytime. (publisher abstract modified)

Date Published: January 1, 2020