Practice Profile: Red-Light Camera Interventions for Reducing Traffic Violations and Crashes

Cohn and colleagues (2020) conducted a meta-analysis on the effectiveness of red-light camera interventions on the incidence of red-light camera violations and the incidence and severity of traffic crashes. This analysis updated a previous smaller systematic review by Aeron–Thomas and Hess (2005), which searched studies published 2002 or earlier, by broadening and expanding the literature search and using a more detailed meta-analysis. A four-part search strategy identified literature including (1) searching online electronic bibliographic databases for published and unpublished evaluations of red-light cameras; (2) searching the websites of international institutes and research agencies focusing on transportation issues for reports and other gray literature; (3) searching the reference lists of published studies to identify additional published and unpublished works; and (4) conducting a keyword search using Google and Google Scholar to search for additional gray literature. The review searched for studies up to June 12, 2015.

To be eligible, studies must have assessed the impact of red-light cameras on red-light violations and/or traffic crashes. Studies must have employed a quantitative research design that involved randomized controlled trials, quasi-experimental design, a controlled before-after design, or a controlled interrupted time series. Qualitative, observational, or descriptive studies that did not include formal comparisons of treatment and control groups were excluded from this research. Research that included interventions such as speed cameras or enhanced police enforcement were excluded. Studies were eligible regardless of the country in which they were conducted or the date of publication. Comparison groups received normal routine traffic enforcement. Police still could issue citations for traffic violations at control intersections during the study period.

Eligible studies had to measure and report data on at least one of the following outcome measures:

• Red-light violations, based on the number of vehicles passing through a junction after entering on a red light.
• Number, severity, and type of road traffic crashes. This may include the number of total crashes, the number of crashes resulting in injury, the number of property-damage-only crashes, and the number of specific types of crashes (e.g., rear-end crashes; right-angle crashes).

The CrimeSolutions review of this meta-analysis focused on the following outcomes of interest: total number of crashes, total number of crashes resulting in injury, total number of property-damage-only crashes, and total number of red-light-running crashes. Red-light-running crashes were identified as those caused directly by a driver running a red light or failing to yield during a turn on red or any crash in which a red-light violation ticket was issued.

To facilitate comparisons between and among studies, a standardized summary measure based on relative effects was defined for each outcome. Summary measures were based on relative effects, rather than differences in effects, where the outcome after intervention was divided by the outcome before intervention, as an expression of the proportional change in outcome. Summary measures were calculated for all studies when possible. Rate ratios were estimated by dividing the count of the outcome post-intervention and pre-intervention in the intervention area by the corresponding ratio in the control area. Results were pooled in the meta-analysis when at least three studies reported the same outcome; otherwise, the results of individual studies were described.

This analysis examined 38 quasi-experimental studies (including 10 studies from the previous analysis). No randomized controlled trials were found. Most of the 28 newly identified studies were conducted in the United States (20 studies), with studies also from Australia (5 studies), Canada (2 studies), and Singapore (1 study). The newly identified studies were published between 1981 and 2016.