Red light cameras reduced the occurrence of severe right-angle and left-turn crashes while the number of rear-end crashes increased.
Experience with automated red light running enforcement in Arizona.
Made Public Date


United States


United States

The Impact of Red Light Cameras (Automated Enforcement) on Safety in Arizona

Summary Information

Red light running cameras (RLCs) have been used as a countermeasure to reduce red light running and associated crashes in a number of US cities; however, there are few evaluations of their effect on motor vehicle crashes and crash costs. This study prepared by the Arizona DOT in 2005 was designed to estimate the safety impacts of RLCs on traffic crashes at signalized intersections in the State of Arizona. The scope of the study was to compare and contrast the impact of the RLC on safety at approaches with installed cameras and the impact of the RLC on safety at all approaches, testing for the spillover effect of the RLCs on non-camera approaches.

Surveys were distributed to 5 jurisdictions. After the findings of the surveys were summarized, two jurisdictions, Phoenix and Scottsdale were found to provide the most relevant data and therefore were selected as the basis for further analysis. The survey responses and the data collected during site visits were used to develop the datasets necessary to evaluate the safety effectiveness of the RLCs and develop clear and concise operational definitions needed to conduct the analysis.

Four evaluation methodologies were designed and applied for this study:
  1. A simple before-after study.
  2. A before-after study with traffic flow corrections.
  3. A before-after study with a comparison group.
  4. An empirical Bayesian analysis to correct for potential regression-to-the-mean effects.
The crash benefits are estimated in two ways: direct effects and spillover effects. Spillover effects are analyzed by separating the intersections with cameras from the non-camera equipped intersections.


City of Phoenix

  • Right angle crashes were reduced 14 percent.
  • Left-turn crashes were reduced 1 percent.
  • Rear-end crashes increased 20 percent.
  • Spillover effects did not appear to be present.
City of Scottsdale
  • Right angle crashes were reduced 17 percent.
  • Left-turn crashes were reduced 40 percent.
  • Rear-end crashed increased 45 percent.
  • Spillover effects were present and were relatively high.
In both cities, the programs had a positive economic impact due to the greater severity of right-angle and left-turn crashes. In Scottsdale, experience showed a larger impact on fatal and injury crashes, and therefore a larger economic impact than in Phoenix.
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