About one in five Americans lives in one of the roughly 700 counties or cities that have signed contracts with private firms to install street cameras to record drivers who speed or run a red light. In theory, those systems sound like a good idea. Knowing they can be filmed, drivers might behave better. The vendors say that their cameras are one reason why traffic deaths have been falling.
On the other hand, drivers also sometimes overcompensate by accelerating when the light turns yellow, or slamming on the brakes so that the car behind goes into them. Critics therefore say that the evidence is mixed, and that traffic deaths have fallen for other reasons, such as safer cars and fewer miles driven.
But aside from that debate, many drivers object to getting a big fine for that most American of peccadillos, the so-called "rolling stop" (not actually a stop at all) when turning right on a red light. A nationwide backlash is occurring, as residents vote the cameras out in referendums and cities try to cancel their contracts with vendors.
Phineas Baxandall at the US Public Interest Research Group, a non-partisan advocacy, says the trend toward privatising the enforcement of traffic laws poses inherent conflicts of interest. Municipalities typically sign up because they are strapped for cash. When the contract involves revenue-sharing between the vendor and the municipality, there is an incentive to issue more tickets than necessary. But even flat-fee contracts can cause problems, if the system is implicitly tuned to recoup that fee by, in effect, setting a quota of tickets to be issued.
Karen Finley, the boss of Redflex Traffic Systems, one of the three largest vendors, denies any such conflict of interest. "We provide just one more tool for law enforcement," she says. "We don't even decide who gets a ticket; that is all done by a police officer." The problem, counters Mr Baxandall, is that this police officer works for a city or county and has a boss and a budget.
As cities from Houston, Texas, to San Bernardino, California, have discovered, getting rid of the systems is usually not a cheap option either, because contractual obligations lead to fines or litigation. Cities that have not yet signed up, says Mr Baxandall, may do better to build a roundabout at an intersection instead, or put flashing lights at crossings.