Chicago has been installing red light cameras. I thought one caught me a few weeks ago, but never got a ticket, so the flash must have been for a car going the opposite direction. The experience got me wondering about certain aspects of the systems.
If you search, you’ll find opinions that they are effective at reducing accidents, and others that they are not. The only definitive RLC study I found, conducted by FHWA, has interesting conclusions. Bottom line is red light cameras reduce both injuries and costs. The FHWA study is much better than others, but it’s important to note it’s limitations.
The FHWA study discusses spillover effect, that is, the effect where RLCs alter the behavior of drivers at intersections without RLCs. When a city places RLC’s at a few intersections, some drivers pay attention to whether a intersection has a camera, but others become more careful at all intersections.
What the study can’t measure, because there is no data for it, is what the effect would be if all drivers acted like the second group, that is, they drove more carefully at all intersections. This condition would occur if all intersections had cameras or a high enough percentage as that drivers assumed they were present without looking for them.
This limitation is important because all the benefits of this homogenous state, compared to the current mixed state, favor RLCs. First, in the mixed state, drivers intentions and expectations vary more than in the homogenous state. If a driver who knows a RLC is not present at an intersection is following one assumes all intersections are equipped, the following driver may assume the leading driver is less likely to stop than he is, increasing the risk of a rear-end collision. If all drivers have similar goals, the risk is reduced.
Second, if drivers look for RLCs as they approach an intersection, this is a distraction, and increases the risk of any type of accident, especially rear-end collisions. If they assume the camera is present, plan to stop, and focus their attention on traffic and signals, the risks are lower.
The point is the proven, but modest benefits the FHWA study finds are underestimating the full value, and while we may each dislike the chance we’ll receive a ticket, ultimately they do save lives, injuries and costs.