When a stoplight turns yellow on an approaching driver, that person makes a quick decision about whether to keep going or to put on the brakes.
In between lies an area of indecision that transportation experts call the “dilemma zone,” when drivers must make a quick judgment call. Stop too sharply and risk being rear-ended, or keep going and risk a ticket or even an accident.
City Council Member Charlie Gerdes wants to make it easier for motorists by programming stoplights to stay yellow longer at the 10 intersections where red-light cameras operate. The City Council is due to discuss the proposal Thursday.
Studies show that doing would reduce accidents, Gerdes said.
“It indisputably has measureable safety improvements,” he said. “This is an improvement we could make, and it doesn’t have any revenue attached to it.”
Some studies do point to reduced red-light running with longer yellow intervals or from longer clearance intervals — the half-second when all the lights at an intersection are red.
But there is not universal agreement those measures work.
The change may work in the short-term, but drivers eventually adjust to the new timings, said David Hurwitz, an assistant professor of civil engineering at Oregon State University.
“People are smart consumers of transportation,” said Hurwitz. “When the lights were longer on all red, it increased rates of disobedience.”
Yellow light times in St. Petersburg vary from four to five seconds. City traffic engineers follow minimums established by the Institute of Traffic Engineers that include factors such as the speed limit, the width of an intersection, visibility and the grade of approach roads.
“You use the formula unless you have a good engineering reason to modify or lengthen the yellow time,” said Joe Kubicki, the city’s director of transportation. “It’s not seen in the traffic engineering field as way to reduce accidents.”
Florida Department of Transportation officials will not recognize increased safety as a reason to lengthen yellow times on state roads they administer, Kubicki said.
About 26 percent of all crashes in St. Petersburg in 2010 happened at intersections with traffic signals, according to a city report. The statistic was one that city officials cited to support the city’s 2011 decision to install red-light cameras.
Studies that say longer yellow-light intervals reduce crashes include a 2004 study by the Texas Transportation Institute, which reported a decrease in accidents of as much as 40 percent when the yellow-light duration was increased by one second.
City officials only need look at their own red-light camera data for proof that longer yellow lights reduce red-light running, said Matt Florell, owner or a local software company who runs a website advocating against red-light cameras.
One city intersection with a 4.3-second yellow interval caught almost three times as many red-light runners as a nearby intersection, where the light remains on yellow for five seconds, according to city data.
“The data in our city points to the fact that longer yellow lights would significantly reduce red-light running,” Florell said.
Gerdes, who recently voted in favor of continuing the city’s red-light camera program, said his proposal is focused merely on safety. If it is successful, he would like to extend it citywide.
“If your trip is few seconds longer but no one is getting hurt, that’s an acceptable trade-off to me,” Gerdes said.