traffic Q&A Question: Reader Pam Paul of Tacoma wrote in with this “what’s up with that?” question:

“I commute from west Tacoma to Seattle and back each work day. On my return trip, I exit I-5 to westbound SR16. On the westbound lanes of the exit from I-5 to Highway 16, right before the viaduct, there are two rumble strips. I’m curious what their purpose is?”

Answer: Washington Department of Transportation spokesperson Jamie Swift came up with this detailed explanation:

“Rumble strips are grooves or rows of raised pavement markers placed perpendicular to the direction of travel to alert inattentive drivers. As a vehicle passes over the rumble strips, noise and vibration are produced, alerting the driver they are approaching a hazard.

“Roadway rumble strips are placed across the roadway to alert drivers approaching a change of roadway condition or a hazard that requires substantial speed reduction or other maneuvering.”

Rumble strips are also used on shoulders and centerlines to alert drivers when they are drifting off the road or into the wrong lane.

P.S.: Paul added this bit of praise for the DOT folks, who don’t always feel loved: “I must say that despite the construction work to replace the Nalley Valley viaduct, the WSDOT should be commended at how little impact that project has had on traffic. It slows down a bit across the viaduct, but it could be a lot worse. Thanks.”

Got a question about traffic congestion, construction, spending or other transportation issues? Send it to traffic@thenewstribune.com. Include your name, hometown and daytime telephone number. We’ll answer as many as we can. Find an archive of previous answers at www.thenewstribune.com/news/traffic/qa.