CHICAGO—A substantial city revenue source is under fire as Mayor Rahm Emanuel announced 9,000 drivers would be allowed to contest tickets they received from red-light cameras.

Since 2007, the city of Chicago has issued more than 4 million tickets via red-light cameras, bringing in more than $400 million, according to the Chicago Tribune.

Questions over the validity of many of the tickets, as well as skepticism surrounding the safety benefits of red-light ticket cameras has put the mayor’s office back on its heels.

Emanuel announced the review policy just days after the Tribune published a 10-month investigation that reported “thousands” of the tickets issued via red-light cameras came during short periods of specific times, while there were major lulls in ticket over other, extended periods of time. This suggested that perhaps the city was purposefully manipulating the system to assign more tickets at certain intersections or during certain times.

“The analysis of more than 4 million tickets issued since 2007 found cases where intersections that had issued just a few tickets a day temporarily began spewing them at rates of up to 56 per day,” reported the Tribune. “A phenomenon that traffic engineers shown the research say is likely the result of faulty equipment, human tinkering or both. City transportation officials have acknowledged that faulty equipment is a likely culprit in some of the ticket surges.”

For its part, the city said the numbers in question are nothing more than random variations.

“There are always spikes in any automated enforcement program due to fluctuations in traffic volume and driver behavior,” Transportation Commissioner Rebekah Scheinfeld told aldermen at a recent City Council committee hearing. “When traffic is impacted by normal construction, special events, or even weather, we cannot always predict where traffic will be pushed, but it is normal for drivers to find their own alternative routes that could include red light cameras.”

Emanuel said the public trust has been breached and the city must work to gain it back.

“If any of the 9,000 are wrong, they’re going to get a refund because they deserve it,” the mayor said in a statement. “There should be no inequity in the system. There should be no aberration. Even though it’s a small percentage—less than 1 percent—it has to be 100 percent right for there to be trust.”

2007 comparative study conducted by the Virginia Transportation Research Council found that red light cameras had “no demonstrated value” for increasing safety in the tested areas.

The VTRC analysis suggested, “red-light running crashes decreased but that rear-end crashes (where a following vehicle strikes the rear of a leading vehicle) increased after the cameras were installed,” and therefore no net increase of safety could be proclaimed. In fact, accidents increased by 27 percent in the tested areas, according to the VTRC.

Similarly, a study from the Insurance Institute for Highway Safety found that “cities using red-light cameras had an estimated higher rate of red light-running fatalities, specifically 25 percent, than cities that did not use red light cameras.”

The IIHS research suggested that while fewer drivers were speeding up to try and beat red lights because of the cameras, many more were slamming on their breaks and causing rear-end accidents.

“Studies have shown that these cameras have mixed results,” said Abolfazl Mohammadian, a professor of civil and materials engineering at the University of Illinois-Chicago. “They have been successful in some locations, but the main reason for the places they fail is commuters get comfortable on their normal routes, but when they’re forced to change routes [because of construction or other reasons] they don’t allow enough time or are unfamiliar with the streets. They speed up and try to make up for the time they’re losing.”

Mohammadian said the main problem caused by red-light cameras are rear-end accidents caused by careful drivers trying to make sure they don’t enter the intersection too late and get cited for a ticket.

Read more at Watchdog.org.