Day in and day out for at least 30 years (and perhaps for almost a century), over 3,000 stoplights all across Chicago have whirred through tens of millions of cycles the exact same way: green, then yellow for three seconds, then red. Yet today, this three second cycle was suddenly declared a public safety emergency, with the Tribune’s front page fomenting panic about the crisis posed by “risky” and “too short” yellow phases.
The Tribune, of course, has long pursued a vendetta against the automated enforcement of red lights in Chicago, consistently whining about a program that penalizes criminals who blow through stoplights with deadly consequences. In its newest episode, the newspaper assembled a cadre of experts to inveigh against the long-established three second yellow phase, and arguing for a few tenths of a second more leeway. (This isn’t the first time the Tribune has zeroed in on fractions of seconds in arguing against enforcement.) Drivers, it seems, feel as if they’ve been “ambushed” by yellow lights that work exactly the same way they’ve worked for decades.
One example the Tribune cites approvingly is Maryland, where a 2004 law lengthened the minimum yellow signal phase to 3.5 seconds. Yet the story there was all about political perception, rather than engineering standards. Frank Murphy from Baltimore’s transportation department told the Tribune, “The reason the law was passed was because it was represented that there was an ambush situation, when yellow lights were set so low – even though they had always been set at three seconds previously.”
True, some recent engineering guidance recommends that cities assume that drivers are usually speeding when approaching traffic signals, and such formulas find Chicago’s yellow signals to be on the short side. For example, Institute of Transportation Engineers’ formula recommends that for situations like a citywide standard (where actual travel speeds can’t be observed), adding 7 mph to the speed limit across the board — thus assuming that drivers citywide are traveling at 37 mph.
Moving forward with that assumption would endorse and enable speeding, which is a far cry from the Chicago Department of Transportation’s recent push to eliminate all fatalities from our streets. David Zavattero is head of traffic safety programs at CDOT, and oversees the red light camera program. He said that Chicago uses a three second yellow light because “we don’t believe it is a safe environment to be [in], basing your signal timing on a 40 mph vehicle traveling through the intersection.” Plus, Chicago’s citywide three second phase has a long history: The federal government’s Manual on Uniform Traffic Control Devices first recommended a three second minimum back in 1935, and continues to do so today.