Traffic Q&A: In which we explore yellow lights and ‘for sale’ signs

Q: How long should a traffic signal light be yellow? I have never seen that information listed anywhere, but the yellow lights seem to vary in length at various locations.

I think the yellow lights should last at least three seconds to allow a vehicle that is too near the intersection to stop in time to proceed through an intersection without being cited for running a red light. – David L., Tacoma

A: We here at Traffic Q&A headquarters think they should always be yellow long enough for us to get through the intersection, but we suspect David wants a more objective answer.

So we put his question to Josh Diekmann, Tacoma’s traffic engineer.

Said Diekmann:

“The reader is correct — the length of time the signal is yellow varies from location to location.

“The City of Tacoma follows national guidelines for setting the yellow time, known as the yellow-change interval. These national guidelines specify a minimum yellow-change interval of three seconds and a maximum of six seconds, with the higher values being used in locations with higher speeds.”

The yellow lights at most intersections in T-town are set to 3.5 seconds, Diekmann said. The city also has added an “all-red clearance interval,” which means the signals are red in all directions, of 1.5 seconds at most intersections.

“These yellow and all-red times are designed to allow enough time for drivers to navigate the intersection safely,” he said.

Diekmann added that a yellow light should not be interpreted as a signal to hurry up.

“When the yellow light turns on, a driver must stop if it is safe to do so,” he said. “If the driver already is in the intersection when the light changes, they should continue through the intersection.”

Choose your course wisely, my friends, or you might be seeing lights of a different sort: blue and flashing.

From the “I’ll be darned” file: While researching an earlier column about eating and driving in Tacoma, we stumbled across another Tacoma traffic code that made us do a double take.

It is 11.05.564, titled “Parking with ‘for sale’ sign.”

To wit:

“It is unlawful for any person, firm, association, co-partnership or corporation, being the owner, or acting as agent for the owner of, or having charge or control of, any motor vehicle, to stand or park the same upon any of the streets, avenues, alleys, or other public places in the City of Tacoma, with a ‘for sale’ sign thereon, for the purpose of offering or exposing the same for sale, barter or exchange.”

There’s more: “Every person who violates any of the provisions of this section shall, upon conviction thereof, be fined in any sum not exceeding $100.”

A mean judge also would require violators to draw a sentence diagram of the section. Dude, that’s a lot of commas.

This story was originally published March 20, 2016 at 6:00 AM with the headline "Traffic Q&A: In which we explore yellow lights and ‘for sale’ signs."