This week Governor Pat Quinn of Illinois signed legislation that will allow the City of Chicago to put speed cameras in the one-eighth mile buffer zones around schools and parks. As the Chicago Tribune has reported, the City has more than 600 public schools and only slightly fewer parks, so this legislation gives Chicago the authority to cover roughly half of its territory with speed cameras. The City says it will concentrate on the approximately 80 areas where the need for speed enforcement is particularly acute.
Although Quinn signed the legislation, the cameras are the handiwork of Mayor Rahm Emanuel. The Mayor says he developed the plan after school officials and the police expressed concerns about public safety. Emanuel’s critics—and he has a lot of them—paint the legislation as being more about revenue generation than public safety. Drivers who go more than 5 miles over the speed limit will be fined $50 and drivers who go more than 11 miles over the limit will be fined $100. The Mayor has said repeatedly that he doesn’t care if the cameras generate any revenue; the legislation is all about keeping kids safe.
Let’s take the Mayor at his word and assume that his only goal is to make Chicago safer. What would traffic engineers and behavioral economists advise? They would tell him to install dynamic speed displays, which announce the posted speed limit and display in large digital numbers the speed of each driver going past. One of the first experiments with these displays took place in school zones in suburban Los Angeles in 2003. Drivers slowed down by an average of 14 percent and in some zones the average speed dropped below the limit. The use of dynamic speed displays has since become commonplace and research has consistently shown that they cause drivers to slow down by about 10 percent for several miles.
These displays upend the usual approach to traffic enforcement because there is no penalty for displaying a speed that is higher than the posted limit. Instead, the display works by creating a feedback loop: (1) sensors instantly capture and relay information about the driver’s speed; (2) the large public display of numbers carries real punch because few people want to be perceived as reckless or careless; and (3) the driver has immediate opportunity to slow down by simply easing up on the gas. This feedback loop is so effective that traffic safety experts have concluded it does a better job of changing driving habits than techniques that depend on police issuing tickets. (You can read about dynamic speed displays and feedback loops more generally here.)
Chicago’s speed cameras will be accompanied by highly visible signage, so time will tell whether the combination of signage and speed cameras make drivers slow down in the short term and change their driving habits in the long term. If I were advising a mayor whose priority was public safety, however, I’d recommend the use of dynamic speed displays that provide effective feedback to drivers in the moments before they enter a school zone, and not cameras whose feedback comes in the mail several days after the driver already has sped by a school.