Today, for the first time ever, speed limit enforcement cameras are up and running in New York City. To determine where cameras would have the greatest impact on reducing speeding, the New York City Department of Transportation (NYC DOT) identified 100 schools where drivers speed more than 75 percent of the time. The State law authorizing the City’s use of speed cameras, however, limits the program to just 20 cameras which must be placed within one-quarter mile of those schools.

With only one-fifth of these danger zones covered at any given time, how effective can the speed camera program be?

A study on the effectiveness of speed camera enforcement in Montgomery County, Maryland found that “highly visible automated enforcement can promote community-wide changes in driver behavior.” The researchers found that on streets with both cameras and warning signs, there was a 70 percent reduction in speeding 10 mph over the speed limit. Streets with only warning signs, but no cameras, saw a 39 percent decrease in speeding, and there was even a slight reduction (16 percent) in speeding on streets with no cameras or warning signs. This phenomenon has come to be known as the “distance-halo effect.”

To measure the effectiveness of the distance halo, researchers analyzed the change in the number of injuries as a result of motor vehicle crashes in areas around 49 speed camera sites in Cambridgeshire, England between 1990 and 2002. The researchers found that within 250 meters (.15 miles, or three north-south Manhattan blocks) of speed camera installations, injuries resulting from crashes fell by an average of 46 percent. Within 500 meters (.3 miles/six blocks), injuries dropped 41 percent; 32 percent at 1000 meters (.6 miles/blocks); and 21 percent at 2000 meters (1.2 miles, or 24 blocks).

If speed cameras have the same impact in New York as they’ve had in Cambridgeshire, a speed camera installed near PS 270 in Clinton Hill, Brooklyn (where 87 percent of drivers exceed the speed limit) could positively impact driver behavior 1.2 miles away near Atlantic Terminal.

Twenty “distance halos” stretching over a mile in each direction around each camera could help keep speeds down on a great deal of New York City’s streets. But what if drivers don’t know where the cameras are? In New York, the City is not announcing where cameras will be mounted, nor will there be signs posted to warn drivers when they’re in speed camera zones.

The city plans to rotate the cameras to keep drivers guessing in hopes they’ll slow down whenever they’re on the road. “Any school where there’s excessive speeding will be fair game,” said Transportation Commissioner Janette Sadik-Khan. “One of the deterrents is that people don’t necessarily know where they are.”

While the law says the City “may install signs giving notice that a photo speed violation monitoring system is in use,” they are not required to use such signs. By not highlighting the areas that are under camera surveillance, the program could be even more effective. As Transportation Alternatives’ Juan Martinez puts it, when drivers know they’re in a speed enforcement zone,  “that tells drivers it’s ‘okay’ to speed a block later.”