It's well-established that speed cameras can get drivers to slow down, but do the effects hold up over time? IIHS researchers recently returned to the site of an earlier study to find out.
The results, presented in September at the annual meeting of the Governors Highway Safety Association, were impressive. More than seven years after it began, the speed camera program in Montgomery County, Md., a large community near Washington, D.C., has led to long-term changes in driver behavior and substantial reductions in deaths and injuries.
Automated enforcement can be controversial. Some programs have been rolled back because of a political backlash, and some states have outlawed their use. The new study has helped put the spotlight on cameras' lifesaving potential. "Automated speed cameras enforce the law, cost taxpayers nothing and make streets safer for everyone," The Washington Post said in an editorial citing the Institute's research. The newspaper expressed hope that the study would encourage more communities to use cameras.
As of August, only 138 jurisdictions were operating speed cameras. If all U.S. communities had programs like the one IIHS studied in Maryland's Montgomery County, more than 21,000 fatal or incapacitating injuries would have been prevented during 2013.
Speed cameras were introduced in Montgomery County in 2007. As of 2014, the county had 56 fixed cameras, 30 portable cameras and six mobile speed vans. The cameras are used on residential streets with speed limits of 35 mph or less and in school zones.
IIHS originally looked at the Montgomery County program during its first year. Six months into the program, the proportion of drivers traveling at least 10 miles over the speed limit had fallen on streets with cameras (see Status Report special issue: speed, Jan. 31, 2008).
The new study found that cameras have reduced by 59 percent the likelihood of a driver exceeding the speed limit by more than 10 mph, compared with similar roads in two nearby Virginia counties that don't have speed cameras.
The researchers also looked at crashes on camera-eligible roads in Montgomery County, relative to comparison roads in Virginia. They found that the cameras resulted in a 19 percent reduction in the likelihood that a crash would involve a fatality or an incapacitating injury, as reported by a police officer on the scene.
"Speed cameras get drivers to ease off the accelerator, and crashes are less likely to be deadly at lower speeds," IIHS President Adrian Lund says. "This study connects the dots to show that speed cameras save lives."
Although cameras alone are effective, Montgomery County recently found a way to deploy them so that they have a bigger impact.
In 2012, the county introduced speed-camera corridors. With corridors, enforcement is focused on long segments of roads instead of specific locations. The cameras are regularly moved to different locations on those roads so drivers don't become familiar with their exact locations.
The corridor approach led to further safety gains, reducing the likelihood of a crash involving a fatal or incapacitating injury an additional 30 percent beyond the use of cameras alone, the researchers found.
"Speed-camera corridors force drivers to watch their speed for the length of the road, instead of slamming on the brakes at a specific location and then speeding up again," says Anne McCartt, the Institute's senior vice president for research and a co-author of the study.
Overall, the county's camera program in its current form — including the use of corridors and a minor enforcement change that took effect in 2009 — reduces the likelihood of fatal or incapacitating injuries by 39 percent on residential roads with speed limits of 25-35 mph. The estimate of 21,000 fatal or incapacitating injuries that cameras could prevent nationwide is based on that reduction.
The total benefit would likely be even greater because that number doesn't include any spillover effect. Drivers in Montgomery County seem to have slowed down even on roads that aren't eligible for automated enforcement. The researchers found that the likelihood of injuries fell 27 percent on 40 mph roads as a result of the camera program on roads with limits of 35 mph or less.
"The IIHS evaluation of our Safe Speed program validates the fact that a well-managed program that properly deploys its speed cameras can effectively change behavior and reduce the likelihood of collisions," says Capt. Tom Didone, director of the Montgomery County Police Department's traffic division. "Law enforcement programs across the nation will greatly benefit from this report."
Effect of speed cameras in Montgomery County, Md.
Percent change in the likelihood of a crash on a camera-eligible road involving an incapacitating or fatal injury
Public awareness of cameras
Cameras succeed in changing behavior only if drivers know about them. In Montgomery County, 95 percent of drivers surveyed were aware of them. More than three-quarters said they had reduced their speed because of the program, and 59 percent had received a speed-camera ticket personally.
Sixty-two percent of drivers surveyed in Montgomery County said they favored speed cameras on residential streets. That means there are supporters even among those who have been ticketed.