Some traffic signals for left-turn lanes getting a yellow makeover

For drivers, green usually means go and yellow means yield.

But the federal government thought circular green lights in left-turn lanes were sending mixed signals because those drivers must yield to oncoming traffic.

“Your mind is kind of programmed to think green equals go,” said Scott Larson, Coralville's assistant city engineer.

New standards from the Federal Highway Administration will result in flashing yellow arrows replacing the circular green lights at many new left-turn-only lanes.

A few of these new signals have gone up recently in the Iowa City and Cedar Rapids areas.

One is at the reconstructed intersection of First Avenue and Fifth Street in Coralville. The left-turn signals flash yellow, letting drivers know they must yield to oncoming traffic. There also is a sign next to the signal telling them that.

A green arrow still gives drivers a protected left turn before the light turns yellow.

Becky Love, owner of Advanced Billiards on the corner of the intersection, has been impressed, saying drivers seem to understand what to do and traffic has run smoothly.

“I think it's safe,” she said. “People do yield.”

Safety is the goal, transportation officials said.

Federal Highway Administration research found fewer drivers made mistakes when they had a flashing yellow arrow rather than a circular green light. Drivers who made mistakes with a yellow arrow often still waited for oncoming traffic, said Leslie Hart, associate traffic engineer for the city of Cedar Rapids.

“When they misinterpret it, they're more likely to do it in a safer fashion,” she said.

Cedar Rapids this month added a flashing-yellow-arrow signal to the left-turn lane at the intersection of Third Avenue and Eighth Street Southeast. Hart said drivers are responding well to the change.

Cedar Rapids doesn't have plans to swap out a bunch of existing lights. The new signals are recommended for left-turn lanes in which the signal is directly over the lane. Cedar Rapids is unusual in that many of its signals are over the lane line between the through lane and the left-turn lane, and the “green ball” type of display is still the recommended alternative there, Hart said.

Iowa City and Coralville also don't have set plans for switching to the new lights, although Iowa City will add them when new signals are installed or existing signalized intersections are reconstructed.

Existing intersections are grandfathered in, said Darian Nagle-Gamm, traffic engineering planner with Iowa City.

Also, they're not necessary at busy intersections where left turns are not allowed when oncoming traffic has a green light.

Iowa City this month added a flashing yellow arrow at an intersection on North Dodge Street by Interstate 80. As in Coralville and Cedar Rapids, it's been so far, so good.

“It seems like it's been pretty intuitive to everyone,” Nagle-Gamm said.

A typical five-section signal head costs $800 to $900, Hart said. The ones with flashing yellow arrows are smaller and cost slightly less, she said.

Nagle-Gamm said Iowa City can rewire its signals and add one section for the yellow arrow for about $100.