Multijurisdictional Safety Evaluation of Red Light Cameras

Abstract

The use of red light camera (RLC) systems has risen dramatically in the United States in recent years. The size of the problem, the promise shown by RLC systems in other countries, and the paucity of definitive U.S. studies have motivated a multijurisdictional U.S. study. The fundamental objective of this study, which was sponsored by FHWA, was to determine the effectiveness of the RLC systems in reducing crashes at monitored intersections as well as jurisdictionwide. Phase I involved the development of a detailed experimental design that included collection of background information, establishment of study goals, selection of potential study jurisdictions, and specification of statistical methodology. In Phase 2, an empirical Bayes before-and-after study used data from seven jurisdictions across the United States, with a total of 132 treatment sites. Effects detected were consistent in direction with those found in many previous studies—a decrease in right-angle crashes and an increase in rear-end crashes—although both effects are somewhat lower than those reported in many sources. The extent to which the increase in rear-end crashes negates the benefits for right-angle crashes is unclear and points to the need for an examination of the economic cost of crashes, which is the subject of a companion paper, to aggregate the effects on rear-end, right-angle, and other crash costs. That second paper seeks to isolate all factors that would favor the installation of RLC systems by using the aggregate economic benefit as the outcome variable. There were weak indications of a spillover effect, which point to a need for a more definitive, perhaps prospective, study of this issue.