Transcript for What Chicago Did With Red Light Cameras That Raked in Money
Next tonight, one American city under fire for a small change, so small, it's almost undetectible under drivers caught wind of it. The timing of the yellow lights had been changed. Here's David Kerley. Reporter: The flash. A red light camera caught you. And in Chicago, thousands were caught and fined when the city, without making it public, started ticketing on a shorter yellow light. Here's what they did in Chicago. The national requirement is that the yellow light be no shorter than three seconds. But Chicago decided to go 2.9 seconds. It says, within the margin of error. A tenth of a second. That really makes a difference? Oh, yeah. Just since spring, another 77,000 tickets, and nearly $8 million in fines. A national motorist group called Chicago's ticketing nothing more than a cash grab. We are relying on governments to be fair and transparent and to help improve safety. Rather than using speed cameras as just another way to raise money. Reporter: Not only are cities criticized for using red light cameras for making money, studies show shortening yellow lights can lead to more accidents and deaths. A federal study says increasing yellow light time by one second cut severe red light crashes by 40%. In Chicago, they've stopped ticketing at 2.9 seconds. But it looks like the tickets will stand. And a mystery.
This transcript has been automatically generated and may not be 100% accurate.