Red light cameras can reduce crash-related injuries

Apr 19 2005

Red-light cameras can reduce the number of injuries from car crashes at intersections by up to 30 percent, according to a new worldwide review of studies.

Publication of the systematic evidence review comes as many localities are installing the cameras over the objection of opponents who contend they are merely municipal revenue-raising devices that invade motorists’ privacy.

Red-light cameras could be important in reducing the number of dangerous right-angle collisions at intersections, and have advantages over increased police enforcement in that they run 24 hours a day and do not involve high-speed chases, says lead author Amy Aeron-Thomas, a researcher with the British charity organization Roadpeace, and colleagues. The cameras also are “immune from charges of discrimination, as they detect only those vehicles that have violated a traffic signal,” she says.

The review included studies from the United States, Australia and Singapore, with the highest-quality study from Oxnard, Calif., finding a 30 percent reduction in the rate of crash injuries.

The review appears in the April issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

Although red-light cameras have been operating since the 1970s on several continents, most widely in Europe, very few studies exist on how the cameras affect the number of traffic violations and crash injuries at camera-rigged intersections in the scientific literature, Aeron-Thomas says.

“Many of the included studies, even those several years old, came from Web sites and from reading related material, and not from the literature search of the transport and public health databases,” Aeron-Thomas says.

Aeron-Thomas says that drivers who run red lights are among the leading causes of crashes at intersections with traffic signals. “While most of these crashes are damage-only, many can be serious, as speed and side impacts are often involved,” she says.

The reviewers analyzed 10 studies comparing traffic violations and car crashes at signaled intersections before and at least one year after red-light cameras were installed. Many of the studies indicated a 10 percent to 20 percent reduction in crash-related injuries after the cameras were installed, but most of the studies had some statistical flaws.

For instance, many studies did not account for the problem of “spillover,” Aeron-Thomas says.

“As red-light camera programs involve publicity campaigns and warning signs, behavior in general may be influenced, with drivers inclined to obey red lights at all signalized junctions, thus reducing the risk of collisions at noncamera sites,” she explains.

Although the spillover effect can be good for overall public health, it makes it difficult for researchers comparing camera and noncamera sites in the same region. To remedy this, Aeron-Thomas suggests camera sites should be compared to noncamera sites in areas away from publicized red-light cameras.

In the Oxnard, Calif., study, there were no signs posted at the intersections warning drivers about the cameras, but there were warning notices in the general road areas where the cameras operated, according to review. The Oxnard study did account for the spillover effect, and found a 30-percent reduction in crash-related injuries at the intersections after the cameras had been in place for 20 months.

Richard Retting, a researcher for the nonprofit Insurance Institute for Highway Safety who conducted one of the studies examined in the review, says, “It is apparent from the scientific evaluation of red-light cameras that they reduce red-light violations and prevent thousands of crashes that occur from such violations. The public overwhelmingly supports camera use.”

A 2001 survey in the research journal Transportation Journal found that 64 percent of Americans support the use of red-light cameras. A 2000 study by the Insurance Institute for Highway Safety suggests that 75 percent of Americans, especially those living in large cities, support the cameras.

More than 100 U.S. cities — including New York, Los Angeles and Chicago — employ red-light cameras. Installation plans have often caused political battles in state legislatures, and in Virginia, lawmakers recently passed legislation removing the cameras after 10 years of use.