Red Light Cameras (RLCs) are a popular measure to reduce red-light running and improve intersection safety. However, they may not always be effective, and their impacts on broader driver behavior are not fully determined. The objective of this report was to assess the effectiveness of RLC systems in reducing various types of intersection crashes and the impact of RLC systems on driver behaviors such as approaching speed and responses to yellow signal phases.
To perform this analysis, researchers evaluated the effectiveness of RLC deployments at 27 different intersections across Maryland. They also directly investigated the impact of RLCs on driver behaviors by performing empirical observations at two RLC intersection clusters and analyzed the results to determine responses to the presence of RLCs.
Findings were classified into four categories: Reduction in both side-impact crashes and rear-impact collisions; reduction in side-impact crashes only; reduction in rear-end collisions only; and no influence on rear-end collisions.
When analyzing the effectiveness of the selected 27 RLC deployments, researchers looked at six different time spans: every combination of either three or five years before and after implementation. This was to ensure robustness.
For the analysis of the selected 27 RLC deployments:
- At 24 out of 27 intersections, there was a reduction in the frequency of side-impact crashes after deploying RLCs. Depending on the period of time observed after the deployment, either three or nine intersections showed an increase in side-impact crash patterns after implementation.
- At 10 out of the 27 intersections, there was an increase in the rate of rear-end collisions.
- Overall, RLC seemed to have a positive effect on reducing the severity of the side-impact crashes that did occur. However, the researchers emphasized that this finding was still tentative in nature.
For the empirical analysis:
- The presence of an RLC system reduced the percentage of aggressive drivers at both the intersection with the RLC and at downstream intersections; in one case, an intersection with an effective RLC system had an aggressive driver rate of less than one-fourth that of an intersection without one.
- Drivers were found to be approximately twice as likely to reduce their speed when passing the RLC and encountering a yellow phase, and were similarly between 13 and 33 percent more likely to stop entirely when encountering a yellow phase.
- Advanced warning signs were found to further decrease the percentage of red-light-running vehicles.
- RLCs were shown to have "spillover effect" at immediately downstream intersections, with the safety benefits from their installation carrying over.