As any urban planner, lawyer, or intelligent elected official knows, public safety is a powerful argument in support of measures undertaken by any level of government. This is particularly true of local government, which in the U.S. is responsible for most law enforcement, traffic management, and response to emergencies and disasters.

The city of Chicago in recent years has wielded this argument as the primary justification for a program using red light cameras to monitor traffic at various intersections in the absence of direct management by police officers, who cannot be everywhere. The tradeoff is simple: Violators who drive through red lights or make right turns where not allowed are cited and fined, but those violations do not appear on their driving record. That can only happen if they are cited by a police officer. Violators receive the photographic evidence of their actions in the mail with a notice to pay the fine. The assumption is that the deterrent effect of having to pay the hefty fines will reduce such behavior and make the streets safer, especially in areas near school zones. Most citizens logically assume that the premise is sound, even if the possibility of being ensnared by the law in this fashion can be annoying and deflate one’s wallet.

In the bargain, the city also increases its revenue by the amount of the fines collected, minus the cost of the contract to the vendor operating the system. In a city pinched for cash, as most are, the lure of that revenue can be pretty powerful. The city of Chicago has reportedly collected more than $500 million since the program began ten years ago. It can be hard to part with that money.

All that would probably be acceptable to most people if the premise held water. But the Chicago Tribune paid for a study by the Texas A&M University Transportation Institute to examine the safety benefits of the program and found that it essentially laid a goose egg. Mind you, this program was started under Mayor Rahm Emanuel’s predecessor, Richard M. Daley, more than a decade ago. Emanuel fired the initial contractor, Redflex Traffic Systems Inc., when it became clear that the company had bribed city officials. Now it appears that federal prosecutors have a “bagman” witness who can testify that the company offered city transportation officials incentives of $1,500 per camera to install additional cameras to enlarge the program, which now includes 350 intersections. In short, a program intended to benefit public safety and generate some municipal revenue through fines became mired in corruption. Knowledgeable voters in Chicago would like to be surprised by all this, but, well, you know. We’ve seen this kind of thing before.

What Texas A&M found out undermines the rationale for the program. The city could easily afford to pay for a similar study if it had wanted an honest evaluation of the efficacy of the program, but it has not done so. Basically, in a series that began on Sunday, December 21, the Tribune revealed that the Texas A&M study determined that, while the cameras produced an overall 15 percent reduction in right-angle “T-bone” crashes due to red light violations, it had also produced a 22 percent increase in rear-end crashes. There is a reason for this, one that many drivers in Chicago have instinctively sensed even without statistical data to verify their hunches. The city is using yellow lights that change to red in three seconds, sometimes even just a fraction less. Many of us in the city have had the unnerving experience of slamming on the brakes in the face of quickly changing yellow lights, so it is not hard intuitively to understand how the rear-end crashes would result. The city claims that this complies with a formula developed by the Institute of Traffic Engineers, but the Tribune reports that other cities, like Washington, D.C., and St. Louis, use an ITE deceleration rate that results in a yellow light time of 3.2 seconds in 30-mph zones. Maryland and Michigan use 3.5 seconds, and California and Florida 3.7 seconds where there are red light cameras. Of course, there is discretionary judgment involved, but the more conservative timing is intended to reduce the likelihood of accidents. Chicago uses timing based on posted speed limits and insists that using actual driving speeds, or providing a cushion, the basis for the longer yellow lights, effectively serves to encourage speeding.

But, of course, longer yellows might also result in fewer violations, resulting in fewer fines being imposed. That said, to the extent that shorter yellow lights are inducing, rather than reducing, accidents, the city’s rationale that the program improves public safety becomes a more questionable argument. The city finds itself in the position of possibly causing accidents in order to increase revenue.

The alternative, of course, is to argue to the contrary. The Tribune notes that Chicago Department of Transportation Commissioner Rebekah Scheinfeld defended the program before the city council with a simple before-and-after comparison, showing that accidents had been reduced by 47 percent between 2005 and 2013. But there were flaws in this argument. Even those with a moderately sophisticated knowledge of statistics are aware that picking two years for such a comparison can be very simplistic and subject to manipulation by failing to control for a number of confounding variables. Among those variables, the state of Illinois, during the interim, changed its minimum damage level for required accident reports from $500 to $1,500. That single change accounts for a substantial share of the difference, but is not the only factor complicating the analysis. Nonetheless, the city continues to maintain that the program benefits public safety.

One can excuse Mayor Emanuel with regard to the initial corruption scandal that tarnished the program. That happened on Daley’s watch. But after four years in office, as Emanuel prepares to run for reelection, his support of the Chicago Department of Transportation’s public safety logic makes the program his, even with a new contractor operating it.

The decision to either abandon or fix the program–to produce logical explanations for the locations of cameras, to remedy the positioning of numerous cameras at low-traffic intersections where they may well be causing more accidents than they are preventing–can also be his. Public safety is a powerful argument for municipal traffic management until it falls apart under close examination.

Fix it or give it up, Rahm. Public safety is an awesome responsibility and ought to be taken seriously, no matter how much the city cherishes all that revenue.

Jim Schwab