Why are portions of I-90 near Snoqualmie Pass so ‘groovy’?

Oct 7, 2021, 5:12 AM | Updated: 9:44 am
I-90, grooves...
What's with these grooves? (Chris Sullivan/KIRO Radio)
(Chris Sullivan/KIRO Radio)

I’m back with another question from all my recent driving: What’s with all the random sets of parallel grooves on portions of I-90, east of Snoqualmie Pass?

Chokepoint Challenge: Stay in the right lane to get through traffic faster

I had noticed these grooves before, but I never really thought about them. But when I started seeing them in Idaho and Montana, I figured there had to be a good reason that state transportation departments had created them or installed them.

If you’ve driven to Ellensburg, you’ve probably seen these. There are six parallel grooves, going in the direction of the concrete, about every 20 feet. You’re on them for a while. Then they disappear, only to show back up on another part of the freeway.

I figured they might be for drainage or something like that. A good guess, says Meagan Lott with the Washington State Department of Transportation.

“We get a lot of crazy questions about it,” Lott said. “Some range from do they create more traction in the snow and ice, or are those heating elements that you have installed to keep the snow and ice from building up?”

They are actually for strengthening the concrete panels.

Now, why would you cut grooves in the concrete to make it stronger?

Those grooves are left over from construction where metal rods are inserted in the concrete between two panels to keep them from rocking back and forth.

“It’s part of a maintenance and preservation technique that we use to preserve, maintain, and extend the life of the pavement,” Lott said.

The other question I had is why these grooves are only in the right lane. It’s the same in Idaho and Montana.

That was the simplest part of the equation. The right lane usually takes the heaviest load, with all the truck traffic, so that part of the concrete usually fails first.

Lott said this rod repair is cheaper than a full repaving or concrete panel replacement, and it gives the road a longer life. When putting in new concrete, the contractors install the rods during construction to add the extra strength from the beginning.

Check out more of Chris’ Chokepoints.


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Why are portions of I-90 near Snoqualmie Pass so ‘groovy’?