Yellow arrows get the green light
Published: December 16, 2009
Tags: Federal Highway Administration, John Kugel, Noyce, signals, standards, Traffic & Parking Control Co., traffic control, Wisconsin Department of Transportation, yellow arrow
Traffic engineers still have not perfected the best use of red and green lights to tell drivers what to do.
The Federal Highway Administration sets the standards that dictate the shapes and sizes of signs and the types of street signals, but the rules constantly are changing.
On Wednesday, the administration published its first overhaul of the standards since 2003. When the rules take effect in January, municipalities and state transportation departments must follow the new standards when rebuilding street intersections and placing new signs.
The biggest shift will be an end to green traffic lights that indicate to drivers they can turn left when oncoming traffic clears, said David Noyce, director of the University of Wisconsin-Madison’s Traffic Operations and Safety Laboratory. The lights have caused problems because some motorists think the green light means they can turn without yielding to oncoming traffic, said Noyce, who studied the problem for the Federal Highway Administration.
“It was brought up in the early 1990s,” he said. “So I’ve been working on this thing for a long time, and the reason it was brought up is because there was a safety problem.”
The new rules require governments replace the green lights with flashing yellow arrows when reconstructing intersections or replacing signals. In most cases, local engineers can switch from a green circle to a yellow arrow by reprogramming the software that runs the signals, said John Kugel, president of Traffic & Parking Control Co., a Brown Deer company that sells traffic-control equipment.
Other changes in the administration’s standards, such as traffic signals at pedestrian crossings or timers that count down when it is safe for pedestrians to cross, require more infrastructure work, he said.
The Wisconsin Department of Transportation creates its own traffic-control standards using the federal rules as a base line, Kugel said, so it is impossible to say how the new federal rules will affect Wisconsin.
“I’ll have to wait and see how the state is going to adopt it,” he said.
The Federal Highway Administration standards are intended to prevent the use of different signs and signals, which was a part of the problem with unprotected left turns, Noyce said. Some municipalities and states in the 1990s experimented with signals to replace the usual green light for left turns, Noyce said. Seattle tried flashing yellow signals, Michigan tried flashing red lights, and Cupertino, Calif., tried flashing red arrows, he said.
Noyce studied all of the different signals to see how drivers react. He tested responses with a simulator using a real car with video images projected on a screen wrapping around the vehicle.
Drivers confused by the meaning of a green light while turning left were likely to drive into oncoming traffic instead of taking the cautious approach, he said. The flashing red lights — the street signal equivalent of a stop sign — didn’t work because it impeded traffic, Noyce said.
“From an efficiency standpoint,” he said, “you don’t want to have every car that is able to turn, stop and then wait to proceed.”
The flashing yellow arrow emerged as the best option, Noyce said. Confused drivers usually slowed down or stopped before trying to make a left turn, he said.
“What was significantly different,” Noyce said, “was what drivers did in situations where they didn’t know what to do.”