The Red-Light Camera Miracle

Editor’s Note: Late last year,
The Chicago Tribune performed an independent safety analysis of the city’s extensive red-light camera network. The study concluded that “the cameras do not reduce injury-related crashes overall—undercutting Mayor Rahm Emanuel’s primary defense of a program beset by mismanagement, malfunction and a $2 million bribery scandal.” The study also found that the city’s claims of a 47 percent decrease in side-impact collisions was grossly overstated and that rear-end collisions actually increased. This news prompted NMA ally Jay Beeber, executive director of Safer Streets L.A., to provide the following analysis on why red-light cameras have no positive impact on intersection safety.


The biggest problem with the theory that red-light cameras prevent side-impact collisions is one that is rarely ever addressed—what’s the mechanism by which this allegedly occurs?

Let’s look at the pro-RLC argument. Camera supporters claim that by putting up ticketing cameras, drivers will “adjust their behavior” or “drive more carefully” around the cameras, making the intersections safer. They never go beyond that explanation.

So let’s try to answer the question of how red-light cameras perform their magic. What behavior is being changed or in what way are motorists driving more carefully?

Red-light cameras only target one type of behavior—when a driver could have stopped with a safe and comfortable deceleration rate but instead chooses to “gun it” to try to make it through so they don’t have to stop for the light. I think it’s silly to pretend that this doesn’t happen. It unquestionably does. But not to the extent that many think and usually only when a driver is within the indecision zone. It’s very unlikely that a driver further than about 5-6 seconds travel time to the intersection will try to make it. So the driver who exhibits the behavior targeted by the red-light cameras will, if they fail, run the light by a fraction of a second.

What’s the effect of this? First, let’s consider a driver who does not run the light but crosses the limit line a fraction of a second before the light turns red. In states with a permissive yellow law (meaning that if your vehicle breaks the plane of the intersection before the light turns red, you have not committed a violation, even if the light turns red while you’re still in the intersection) this is perfectly legal. If there’s no all-red clearance interval, cross traffic could start up before this driver makes it across the intersection. Even then, due to start-up delay, there’s unlikely to be a collision, but it could happen, especially if a driver approaching from the cross street sees the light changing ahead and enters the intersection at speed.

Now consider the red-light runner who crosses the limit line a fraction of a second after the light turns red because he decided to go when he could have stopped. What is the practical difference between this driver and the one above? Nothing. That fraction of a second probably has no more likelihood of causing a collision. There is very little, if any, difference in crash exposure due to these two types of drivers.

Of course, with a sufficient all-red clearance interval both of these types of collisions will be avoided.

So let’s say that red-light cameras are 100 percent effective in changing the behavior of the driver who decides to push the yellow (which they are not). What have we accomplished by changing this behavior? Nothing. It’s just not possible to eliminate side impact collisions by scaring drivers into not pushing the yellow because they aren’t the cause of these collisions in the first place.

Now there’s a special case where this could make a difference. With a permissive left turn signal, drivers turning left might think an oncoming driver is going to stop, so they make the turn in front of the oncoming vehicle. The vehicle doesn’t stop and a collision occurs. Of course this can also happen in the scenario where the driver doesn’t run the light and crosses the limit line just before the light turns red. It’s likely that many collisions which are tagged as red-light running collisions are actually ones in which the left-turning driver jumped the gun and then claims the oncoming driver ran the red.

The way to avoid the left turn opposed collision is to have a protected left turn lane and signal. This prevents this type of collision 100 percent of the time.

As for crashes caused by late-into-red red entries, they are due to the driver not recognizing the light is red. Red-light cameras can’t prevent this from happening either so they can’t be effective in reducing or eliminating them.

I’m also not dealing with the length of the yellow light here because I’ll assume for the sake of argument that it is long enough for the vast majority of drivers in the vast majority of situations to either stop or go appropriately.

So I go back to the original question that red-light camera proponents and “researchers” who claim the data show even a modest reduction in red-light running collisions due to red-light cameras are never asked to answer. What’s the mechanism by which red-light cameras have supposedly reduced these collisions?

Their answer is usually the same as the punchline to this famous Sidney Harris cartoon: “Then a miracle occurs.”

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