Traffic Q&A: Many factors play role in crosswalk durations

Staff writerMarch 3, 2014 

Question: Does the city of Tacoma have a standard for pedestrian crosswalk signals?

I’ve noticed that some signals show the solid hand at the same time the light turns yellow, while others show the solid hand several seconds before the light turns yellow. In fact, the intersection of North 26th and Proctor in my neighborhood has both, depending on which street you’re crossing. Why the difference? — Randy Steele, Tacoma

Answer: The city does indeed have standards for crosswalk signals, but they aren’t simple. Timing of the lights is based on guidelines in the Manual on Uniform Traffic Control Devices, an 861-page document published by the Federal Highway Administration.

Generally, the durations of the steady and flashing signals are based on the width of the street and the time it takes to walk across (at an average rate of 3.5 feet per second), according to Leigh Starr, principal engineer in the street operations division of Tacoma’s Public Works Department.

Intervals are set so that a pedestrian stepping off the curb when "Walk" ends (and the flashing "Don’t Walk" starts) has enough time to clear the intersection before the flashing “Don’t Walk” goes to a steady "Don’t Walk."

But the timing can be adjusted based on factors including the volume of traffic, the likelihood of conflicts with turning vehicles and the physical condition of pedestrians. Crosswalks near schools or senior centers, for example, might be adjusted for longer walk times.

"When the green is extended beyond the pedestrian clearance time, a solid 'Don’t Walk' will be displayed until the yellow interval," Starr said.

“For various reasons, one phase may get a green light for longer than the other phase of the cycle in an intersection,” he said.

Rob Carson: 253-597-8693

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