Red Light Traffic Camera. Flickr GSBrown99... Red Light Traffic Camera. Flickr GSBrown99

The first red light camera ticketing system was put in use in New York City in 1993. Since then, 24 states and the District of Columbia have installed red light cameras, while another 15 have banned automated ticketing systems that include red light and speed cameras. You generally don't find that kind of love-hate relationship without something murky going on, and murk is exactly what you step into when you ask this one simple question: Do red light cameras reduce accidents?

That simple question has four answers: Yes, No, Maybe, and It Depends. But it takes a lot of research, a lot of reading, and a lot of money to come to any of these conclusions.

After looking at more than ten studies on both sides of the red light camera argument, the general trends stand up quickly. What is behind them are lots of asterisks and disclaimers, however, such that every one of those four answers is qualified.

Yes, Red Light Cameras Reduce Accidents

The idea that red light cameras reduce accidents is generally true if you are referring to broadside (or "T-bone") accidents. This is the worst kind of collision you can have at an intersection, when a car enters crossing traffic and plows into the side of another car. A slightly greater number of studies showed that these broadside incidents were reduced by red light cameras. A November 2008 study carried out by the Center for Transportation Safety of the Texas Transportation Institute at Texas A&M University found "a 43 percent annualized decrease in right angle collisions" at 56 intersections with red light cameras. A 2007 study by Iowa State's Center for Transportation Research and Education concluded that the "expected average number of crashes per quarter for [red-light-running]-related crashes (non-rear-end) decreased by 40 percent after installation of cameras at intersections with camera-enforced approaches."

The same results were discovered in studies for the Transportation Research Board in 2003 ("angle crashes are usually reduced"), a 2007 study for the Virginia Transportation Research Council ("a decrease in red light running crashes, about 8 percent or 42 percent depending on the statistical method used"), and a 2004 study by the Urban Transport Institute ("one type of accident found to experience a decrease at [red light camera] sites are those involving a left turning car and a car traveling on a different roadway").

But as we suggested before, even those yeses are called into question by other studies. The Washington Post conducted a review of traffic accident data at 45 red light camera intersections during 1999 and 2000, finding that "Broadside crashes, also known as right-angle or T-bone collisions, rose 30 percent, from 81 to 106 during that time frame."

No, Red Light Cameras Don't

Although there are no easy answers, when it comes to argument against red light cameras, the preponderance of evidence is much clearer. While cameras are often credited for reducing broadside accidents, and sometime reducing accidents between cross traffic and those making a right turn on red, they are almost universally credited for increasing rear-end accidents. You have to rummage through a lot of paperwork to find studies, like the one from Iowa State, that claim reductions in rear-end crashes at monitored intersections.

Even the government's look into the matter found that rear-end crashes go up at intersections with the cameras: A 2005 study by the Federal Highway Administration found an average increase of 15 percent in rear-end crashes after looking at 132 locations in seven areas. In the journal of the Institute of Transport Engineers, the group that studies and develops intersection standards, an article that looked at a vast number of studies trying to determine the effects of red light cameras found in almost every case that rear-end crashes increase.

Maybe They Do, Maybe They Don't

Then there is the issue of injuries. While one type of accident said to be most harmful -- the T-Bone -- might be down, but are the increased number of rear-end collisions contributing to more hurt drivers overall? Perhaps.

According to the data, a slight majority of studies also show that injury crashes go up in red light camera-monitored junctions. The Washington Post investigation found, for D.C. at least, a rise in every type of crash, writing, "The analysis shows that the number of crashes at locations with cameras more than doubled, from 365 collisions in 1998 to 755 last year. Injury and fatal crashes climbed 81 percent, from 144 such wrecks to 262."

Countering that is the study from the Transportation Research Board that concluded, "The findings of several studies support that, in general, red light cameras can bring about a reduction in more severe angle crashes with, at worst, a slight increase in less severe rear-end crashes."

But that conclusion is then countered, sort of, by the Virginia Transportation Research Council study that stated, "However, when considering only injury crashes, if the three fatal angle crashes that occurred during the after period are removed from the analysis (the only fatalities that occurred during the study out of 1,168 injury crashes), then the cameras were associated with a modest reduction in the comprehensive crash cost for injury crashes only."

We don't know why you'd remove three fatal crashes during a study period and then draw conclusions based on that, but in fact, this sort of way of thinking is indicative of a lot of what happens with these studies and the conclusions they reach.

Who's Behind The Data?

This is why, frankly, the best answer to the question, "Do red light cameras reduce or cause accidents?", is that it depends on who you ask.

Short of a public outcry or rioting in the streets, states and municipalities are loathe to walk away from easy money, especially when they need it so badly to pay for the very things their populace is crying out for. Red light cameras present a path-of-least-resistance way to get that money. Vendors sign a contract for the cameras that is often cost-neutral, that is, the cities don't have to pay for the camera operation, they just send a cut from each citation to the contract operator. So it's no skin off the municipality's back. What could be better?

That's why you get lots of politicking and doubletalk even in studies that appear to show conclusive evidence of a particular trend, and then more doublespeak when concerned parties get hold of those studies. On top of that you have the liquid nature of statistics itself and the varying methodologies and accepted scientific practices used to gather them.

The Spillover Effect

One of the murkiest areas of red light camera research is something called "spillover effect," which describes the tendency of drivers to change their behavior around other intersections in the area, whether or not they are equipped with red light cameras. Of course, nobody agrees about whether it even exists.

A researcher at the Insurance Institute of Highway Safety (IIHS), went so far as to publicly criticize the Urban Transport Institute study, saying it "ignores the well-known spillover effect."

Actually, the UTI researchers stated up front that, "There is also evidence, also not conclusive, that there is a 'spillover' effect to other signalized intersections within a jurisdiction."

The Federal Highway Administration would only say that, "There were weak indications of a spillover effect that point to a need for a more definitive, perhaps prospective, study of this issue."

But calling into question how the spillover effect is used, one journalist wrote, "Spillover effect is IIHS's trick for giving the cameras credit for reducing fatalities even where they aren't. It assumes that red-light cameras at a few intersections will cause drivers to stop promptly all over town, or all over the county, or maybe all over the state, so improvements outside the cameras' zip codes are credited to them nonetheless. As statistical acrobatics go, this one is breathtaking."

Drawing Conclusions

Do you see where we're going with all this? Mad Hatters and invisible, grinning cats could make more sense than the average motorist of what's really happening. And we're still not finished.

On top of all of that confusion, even though there are red light programs in more than 400 U.S. cities, many studies were conducted within timeframes that simply didn't allow enough time and couldn't gather enough evidence to present black-and-white comparisons of crash data before and after cameras were installed at a single intersection. In other words, some studies lacked a control group.

That is why just about every study we looked at contained a disclaimer that warned, as in the Transportation Research Board study, "Based on the information acquired and reviewed for this effort, it appears that red light running automated enforcement can be an effective safety countermeasure. However, there is currently insufficient empirical evidence based on statistically rigorous experimental design to state this conclusively."

Studies even admit that because the conclusions drawn are all over the graph, nothing definitive can be concluded. From the Virginia study: "These results cannot be used to justify the widespread installation of cameras because they are not universally effective. These results also cannot be used to justify the abolition of cameras, as they have had a positive impact at some intersections and in some jurisdictions. The report recommends, therefore, that the decision to install a red light camera be made on an intersection-by-intersection basis. In addition, it is recommended that a carefully controlled experiment be conducted to examine further the impact of red light programs on safety and to determine how an increase in rear-end crashes can be avoided at specific intersections."

It cannot be expected that cities will step away from red light camera programs, as long as they're making money. But it doesn't help their cases that the only other genuine supporters of red light cameras appear to be the companies that install them, and insurance agencies. Groups like the National Campaign to Stop Red Light Running are funded by Redflex and ATS, two of the biggest RLC operators. The Redflex site has testimonials supporting red light cameras, all of them from city or law enforcement officials.

USA Today published a poll showing that more people strongly support red light cameras, but the poll was conducted by the IIHS, which is funded by the insurance industry.

A key item noted by those who are against red light cameras, though, is the matter of yellow lights. Studies by the ITE have shown that if you slightly increase and standardize the run-time of the yellow light, and leave a slight delay in the cross traffic's transition to green, accidents will be reduced. Still, cities are routinely hauled into court for having made yellow light times ridiculously short -- as if, you know, they're trying to catch people running red lights.

For a final, cynical look at whether red light cameras are truly run for safety or money, take High Point, NC. When the city was court-ordered to pay 90 percent of its citation revenue from red light cameras to the local school system, what did it do? It shut the system down and found a way to break its contract with the operator.

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