Red Light Photo Enforcement Increases Injury Collisions

A recent study from Chicago reported on ARS Technica by Meghan Geuss shows that photo enforcement of red light violations actually increases rear-end injury collisions more than it reduces other types of injury collisions.

The Chicago Tribune in response commissioned a scientific study by two well-regarded transportation researchers, who found that the statistics promoted by the [Chicago] mayor’s office were misleading. According to the Tribune, the authors of the study found a statistically significant, but still smaller, reduction in angle and turning injury crashes by 15 percent, as well as “a statistically significant increase of 22 percent in rear-end injury collisions.” Overall, there was “a non-significant increase of 5 percent in the total number of injury crashes” that happened at intersections with red light cameras when comparing the injury crashes that occurred there before and after the cameras were present.

When I commented via Facebook on this article, a friend who unbeknownst to me has some expertise in traffic safety engineering, replied:

While there are more rear end collisions at camera-controlled intersections (because people drive too close and expect the guy in front to run a red light), the use of red light cameras has reduced the incidence of side impact collisions, which are far more damaging to vehicles and people.

From the National Highway Traffic Safety Administration website:

Question: Do studies show that there are safety benefits from installation of these cameras systems? Do rear-end collisions increase when red-light cameras are installed—in which case, aren’t we just trading one type of crash for another?

ANSWER: Analysis of data in the most comprehensive study to date (Safety Evaluation of Red-Light Cameras, FHWA HRT-05-048, April 2005) from seven jurisdictions (Baltimore; Charlotte; El Cajon, CA; Howard County, MD; Montgomery County, MD; San Diego; San Francisco) at 132 intersections using red-light cameras found:

A 25 percent decrease in total right-angle crashes;
A 16 percent decrease in injury right-angle crashes;
A 15 percent increase in total rear-end crashes; and
A 24 percent increase in injury rear-end crashes.

An economic analysis was conducted to assess the extent to which the increase in rear-end crashes negates the benefits for the decrease in right-angle crashes. This analysis, which was based on an aggregation of rear-end and right-angle crash costs for various severity levels, showed that red-light camera systems do indeed provide a modest aggregate crash-cost benefit. Economic analysis showed that red-light cameras saved society $39,000 to $50,000 annually at each intersection where they are installed. (The costs considered include: hospital bills, property damage to vehicles, insurance expenses, value of lost quality of life, and other costs.)

Primary factors for the greatest economic benefits for red-light camera installation include: locations where there are relatively few rear-end crashes and many right-angle ones, higher proportion of entering average annual daily traffic (AADT) on the major road, shorter cycle lengths and intergreen periods (yellow clearance and all-red), and one or more left-turn protected phases.

A survey conducted by NCHRP found that a majority of jurisdictions (including Boulder, CO; Polk County, FL; Mesa, AZ; Sacramento, CA; Laurel, MD, and others) reported downward trends in red-light running crashes and violations because of red-light cameras. See Impact of Red-Light Camera Enforcement on Crash Experience: A Synthesis of Highway Practice, NCHRP Synthesis 310 (Transportation Research Board, 2003) for more information. This report examines the impact of red-light running camera enforcement on crashes and related crash severity at intersections. The published research reviewed in this report indicates that red-light running automated enforcement can be an effective safety countermeasure.

That’s all good information, but the point of my comment was that the political promoters of red light photo enforcement either don’t understand statistics or they don’t want to. That’s dishonest and unethical. Even $50,000/year/intersection in savings to society is statistically insignificant.

Here in Scottsdale, our public safety director (and police chief) Alan Rodbell is fond of bandying about traffic safety statistics that aren’t even remotely supported by any science. For example, they aren’t baselined for total traffic count, which has declined greatly over the same period for which he touts a reduction in accidents.

I’m hopeful that my friend’s sources (which I have not read) utilize more sound methodology.

Furthermore, poor intersection design (expensive to fix) and poor light timing (incredibly INEXPENSIVE to fix) could both have dramatically greater effect on injury reduction…if that was really the goal. But those aren’t sexy to the politicos because they don’t generate revenue, and they don’t require a big court system with a bunch of employees on the back end.

I would be remiss in not adding that IMHO (unsupported by analysis) whatever societal savings (again, if that’s a legitimate goal) is achieved through red light photo enforcement is probably overwhelmed by the cost paid in higher insurance premiums by those who receive tickets. That, too, is a frequently ignored societal cost.

Having said all that, I’m less opposed to red light photo enforcement than to photo speed enforcement, for which the safety benefit analyses are even MORE sketchy!

If safety is our goal, then (as mentioned by the FHWA study) we should fix the yellow-clearance and all-red phases of our traffic signal timing. Current all-red is almost zero at most Scottsdale intersections. 

I’m very surprised that some tort lawyer hasn’t figured this out and sued the pants off the City, aka the taxpayers.