IIHS Study: Effects of automated speed enforcement
Objectives: In May 2007, Montgomery County, Maryland, implemented the state’s first automated speed enforcement program, with camera use limited to residential streets with speed limits of 35 mph or less and school zones. Changes were made to the program over time. In 2009, a state speed camera law increased the enforcement threshold and restricted school zone enforcement hours. In 2012, the county began using a corridor approach, in which cameras were periodically moved along the length of a roadway segment. The current study evaluated the long-term effects of the speed camera program on travel speeds, public attitudes, and crashes.
Methods: Changes in measured travel speeds at camera sites from 6 months before the speed camera program began (fall 2006) to 7½ years after (fall 2014) were compared with changes in speeds at control sites in the nearby Virginia counties of Fairfax and Arlington. A telephone survey of Montgomery County drivers was conducted in fall 2014 to examine attitudes and experiences related to automated speed enforcement. Using data on crashes during the years 2004-2013, logistic regression was conducted to examine the effects of the program on the likelihood that a crash involved an incapacitating or fatal injury and on the likelihood that a crash was speeding-related on camera-eligible roads and on potential spillover roads in Montgomery County, using crashes in Fairfax County as controls.
Results: About 7½ years after the program began, speed cameras were associated with a 10 percent reduction in mean speeds and a 59 percent reduction in the likelihood that a vehicle was traveling more than 10 mph above the speed limit at camera sites. When interviewed in fall 2014, 95 percent of drivers were aware of the camera program, 62 percent favored it, and most drivers had received a camera ticket or knew someone else who had. The overall effect of the camera program in its modified form, including both the law change and the corridors, was a 39 percent reduction in the likelihood that a crash resulted in an incapacitating or fatal injury. Speed cameras alone were associated with a 19 percent reduction in the likelihood that a crash resulted in an incapacitating or fatal injury, the law change was associated with a non-significant 8 percent increase, and the corridor approach provided an additional 30 percent reduction over and above the cameras.
Conclusions: This study adds to the evidence that speed cameras can reduce speeding, speeding-related crashes, and crashes involving serious injuries or fatalities.