How long is a yellow light? The answer is: A minimum of three seconds, according to federal safety regulations. What happens when a mere tenth of second is shaved off that time and a yellow light lasts 2.9 seconds? If you thought, not much, you’d be wrong.

The city of Chicago and its mayor, Rahm Emanuel, are taking heat—thanks to a Chicago Tribune investigation—for allowing tickets to be given in that extra tenth of a second. The length of yellow lights can actually vary slightly due to fluctuations in electrical power, but before this February the city’s traffic-camera system didn’t issue tickets in any instance when a yellow lasted less than three seconds. When the city changed that lower limit to 2.9 seconds, the impact was substantial: 77,000 additional red light camera tickets were issued, at $100 a pop, which added up to nearly $8 million forked over by unsuspecting drivers.

Here’s more from the Tribune:

The Emanuel administration quietly issued a new, shorter yellow light standard when the city began the transition from red light camera vendor Redflex Traffic Systems to Xerox State & Local Solutions in February. Confronted by complaints from hearing officers and questions from the Tribune about the tickets issued at shorter yellow lights, the administration reversed course in September and told Xerox to re-establish the three-second standard.

Last week, Inspector General Joseph Ferguson issued a review that found that when the city was handing over the contract to Xerox, the administration directed the company to accept red light camera violations for incidents with yellow light times above 2.9 seconds, one-tenth of a second less than the minimum under Redflex. The city previously had told Redflex not to submit tickets with yellows of less than three seconds.

On Wednesday, Emanuel told the Tribune the city went back to the three-second yellow light standard “because trust is the most important” thing. The Mayor is still mulling refunding the ticketed drivers.

Correction, October 20, 2014: This post originally misstated that Chicago’s government had reduced the duration of the city’s yellow lights. The timing of the lights has remained consistent overall but can vary in individual instances due to electrical fluctuations. In February the city changed its policy to begin giving tickets in some cases when, due to fluctuation, the yellow signal lasted less than three seconds.

