Traffic fatalities fell by more than a third after the addition of red-light cameras in 14 U.S. cities studied by the Insurance Institute for Highway Safety, according to a study released today by the researcher.

According to the institute, red-light cameras saved 159 lives between 2004 and '08 in the cities. Had cameras been operating during that period in all large cities, a total of 815 deaths would have been prevented.

"The cities that have the courage to use red light cameras despite the political backlash are saving lives," according to Adrian Lund, institute president.

The researchers selected the 99 U.S. cities with populations of more than 200,000 to compare those with red light camera programs to those without. Because they wanted to see how the rate of fatal crashes changed after the introduction of cameras, they compared two periods, 2004 to '08 and 1992 to '96. Cities with cameras from 1992 to '96 were excluded from the analysis, as were cities that had cameras for only part of the later study period.

The researchers found that in the 14 cities that had cameras from 2004 to '08, the combined per capita rate of fatal red light running crashes fell 35 percent, compared with 1992-96. The rate also fell in the 48 cities without camera programs in either period, but only by 14 percent.

Based on that comparison, the researchers concluded that the rate of fatal red light running crashes in cities with cameras in 2004-08 was 24 percent lower than it would have been without cameras.

And the rate of all fatal crashes at intersections with signals — not just red light running crashes — fell 14 percent in the camera cities and crept up 2 percent in the non-camera cities. In the camera cities, there were 17 percent fewer fatal crashes per capita at intersections with signals in 2004-08 than would have been expected. That means 159 people are alive because of the automated enforcement programs.

This result shows that red light cameras reduce not only fatal red light running crashes, but other types of fatal intersection crashes as well. One possible reason for this is that red light running fatalities are undercounted due to a lack of witnesses to explain what happened in a crash. Drivers also may be more cautious in general when they know there are cameras around.

Based on these calculations, if red light cameras had been in place for all five years in all 99 US cities with populations over 200,000, a total of 815 deaths could have been avoided.

Since the 1990s, communities have used red light cameras to police intersections. About 500 cities now embrace the technology compared with from just 25 in 2000.

Red light running killed 676 people and injured an estimated 113,000 in 2009. Nearly two-thirds of the deaths were people other than the red light running drivers — occupants of other vehicles, passengers in the red light runners' vehicles, bicyclists, or pedestrians.

Without cameras, enforcement at intersections can be difficult and often dangerous. In order to stop a red light runner, officers usually have to follow the vehicle through the red light, endangering themselves, as well as other motorists and pedestrians.

Results in each of the 14 camera cities varied. The biggest drop in the rate of fatal red light running crashes came in Chandler, Ariz., where the decline was 79 percent. Two cities, Raleigh, N.C., and Bakersfield, Calif., experienced an increase.

"We don't know exactly why the data from Raleigh and Bakersfield didn't line up with what we found elsewhere," McCartt says. "Both cities have expanded geographically over the past two decades, and that probably has a lot to do with it."

View the full study at IIHS.org .