What has the Mukilteo Speedway so jammed up lately? Drivers have complained of much longer delays and bad congestion on this major route to I-5 in Snohomish County, but it turns out some of the bad traffic might not be there at all.

Listener Janice Moorhead asked about the Mukilteo Speedway a few months ago. She said it’s been getting bad where the stoplights were added to the highway, near the southeast corner of Paine Field.

The Mukilteo Public Works Department said the highway was designed for about 42,000 cars a day, and it has been handling well over 50,000 cars a day.

The volume increase has been caused by growth in the region and the massive growth at the nearby Boeing plant. Boeing construction contractors have even built a new temporary parking lot for workers just past Harbor Pointe Boulevard, which has added extra cars to the road. They are working on the new 777X factory.

But for months, I have been tracking a big stretch of black on the Washington State Department of Transportation map that runs northbound from Beverly to the Boeing plant. Black on the map indicates traffic is bumper to bumper.

There aren’t a lot of cameras there so I was having trouble quantifying just how bad the traffic was.

On Monday, a day when there was virtually no traffic anywhere in Puget Sound, I watched the black stretch like clockwork all morning.

I called WSDOT and asked if engineers had checked their loop detector there. I was positive it was broken or malfunctioning – and had been for months.

The state sent some engineers out to the site, and they realized it was malfunctioning. They are now working to get it it fixed.

Why didn’t the state realize it was having a problem?

WSDOT said it has thousands of these loop detectors to manage, and sometimes one slips through the cracks.