The city of San Carlos, California was caught last week trapping drivers at an intersection with a yellow time so short that it violated federal and state law. As a result, 411 tickets worth $156,591 will be refunded or canceled, and San Carlos will pay back the cost of any traffic school that a motorist may have taken to avoid license points. The problem was noticed after the city's first and only automated ticketing machine was activated at Brittan Avenue and Industrial Road on November 25. A handful of motorists began to complain to the police that the yellow signal lasted as little as 2.9 seconds, in violation of the federal three-second minimum. The department took corrective action on January 29.

"It was set incorrectly -- we were told it was set for 4.0 (seconds)," San Carlos Police Commander Rich Cinfio told TheNewspaper. "We reset the signal to 3.2."

California Department of Transportations guidelines insist that the yellow time for an intersection like Brittan and Industrial which has a posted 30 MPH speed limit must be no less than 3.2 seconds. Although the difference of less than a third of a second may appear insignificant, it can have a dramatic impact on the number of citations issued by a red light camera. This can be seen in the contract clauses that the private companies operating cameras have created to forbid cities from increasing the duration of a yellow signal ( view example from Mesa, Arizona, 100k PDF).

Going beyond the bare minimum, on the other hand, can have a decisive impact on improving safety. A Texas Transportation Institute study confirmed that when the yellow light timing was increased one second above the minimum amount recommended by the ITE formula, accidents dropped 40 percent (view study). When asked if the city would consider setting the yellow timing back to the 4.0 seconds it expected, a police spokesman sharply rejected the suggestion, even though the longer duration is not prohibited by any contract provision.

"We're comfortable with 3.2 seconds," Cinfio said.

San Carlos and the Australian vendor Redflex Traffic Systems specifically selected the intersection of Brittan and Industrial because it met the most important test.

"Staff estimates it will realize net revenue from any intersection approach wherein the camera captures an average of six violations per day," an October 22, 2007 city memo stated.

The captured violation rate, which includes photographs where the driver or license plate is unclear, far exceeded the rate of six per day. The issued citation rate of seven per day also exceeded expectations. Now the city does not want to lose goodwill over the mistake. On its own initiative, the department moved to contact those who may have paid a citation at the intersection and to clear all improper violations from the books.

"We want to make sure they're made whole," Cinfio said. "Good people do make mistakes. Honesty in government is placed at a premium in San Carlos."