Red light safety cameras have been shown to reduce both red light violations and crashes.
A series of IIHS studies in different communities found that red light violations are reduced significantly with cameras. Institute studies in Oxnard, California, and Fairfax, Virginia, reported reductions in red light violation rates of about 40 percent after the introduction of red light safety cameras (Retting et al., 1999; Retting et al., 1999). In addition to the decrease in red light running at camera-equipped sites, the effect carried over to nearby signalized intersections not equipped with cameras.
A more recent IIHS study in Arlington, Va., also found significant reductions in red light violations at camera intersections one year after ticketing began (McCartt & Hu, 2014). These reductions were greater the more time had passed since the light turned red, when violations are more likely to result in crashes.
Violations occurring at least a half second after the light turned red were 39 percent less likely than would have been expected without cameras. Violations occurring at least 1 second after were 48 percent less likely, and the odds of a violation occurring at least 1.5 seconds into the red phase fell 86 percent.
When it comes to crash reductions, an IIHS study comparing large cities with red light safety cameras to those without found the devices reduced the fatal red light running crash rate by 21 percent and the rate of all types of fatal crashes at signalized intersections by 14 percent (Hu & Cicchino, 2017).
Previous research in Oxnard, California, found significant citywide crash reductions followed the introduction of red light safety cameras, and injury crashes at intersections with traffic signals were reduced by 29 percent (Retting & Kyrychenko, 2002). Front-into-side collisions — the crash type most closely associated with red light running — at these intersections declined by 32 percent overall, and front-into-side crashes involving injuries fell 68 percent.
The Cochrane Collaboration, an international public health organization, reviewed 10 controlled before-after studies of red light safety camera effectiveness (Aeron-Thomas & Hess, 2005). Based on the most rigorous studies, there was an estimated 13-29 percent reduction in all types of injury crashes and a 24 percent reduction in right-angle injury crashes.
Some studies have reported that while red light safety cameras reduce front-into-side collisions and overall injury crashes, they can increase rear-end crashes. However, such crashes tend to be much less severe than front-into-side crashes, so the net effect is positive.
A study sponsored by the Federal Highway Administration evaluated red light safety camera programs in seven cities (Council et al., 2005). It found that, overall, right-angle crashes decreased by 25 percent while rear-end collisions increased by 15 percent. Results showed a positive aggregate economic benefit of more than $18.5 million in the seven communities.
The authors concluded that the economic costs from the increase in rear-end crashes were more than offset by the economic benefits from the decrease in right-angle crashes targeted by cameras.
Not all studies have reported increases in rear-end crashes. The review by the Cochrane Collaboration did not find a statistically significant change in rear-end injury crashes (Aeron-Thomas & Hess, 2005).
When camera programs are discontinued, crash rates go up.
An IIHS study compared large cities that turned off red light safety cameras with those with continuous camera programs. In 14 cities that shut down their programs during 2010-14, the fatal red light running crash rate was 30 percent higher than would have been expected if they had left the cameras on. The rate of fatal crashes at signalized intersections was 16 percent higher (Hu & Cicchino, 2017).
A study in Houston, which turned off red light safety cameras in 2011, found that the camera deactivation was associated with a 23 percent increase in right-angle red light running crashes at the intersections that previously had cameras (Ko et al., 2017).