Why is the 164th Street SW overpass a jam? It’s the flow on the corridor and on the freeway ramps.

We’ve all been there, crawling slowly along approaching a freeway entrance or exit. Vehicles exiting the highway competing for space with the traffic on the surface streets — only a handful of cars making it through intersections each light cycle. This is often expected during peak times, but Janet Moberly, of Mill Creek, was driving through bottlenecks along 164th Street SW near I-5 after rush hour had ended.

Moberly asked; “I am curious why, when headed either direction (on 164th Street SW) at non-rush hour times it takes 10 minutes to get across the freeway. I usually find the problem heading east. Just before Ash Way it slows to a creep and doesn’t clear up until after Meadow Road.”

She’s noticed that sometimes she hits congestion going west, too, through that stretch.

Moberly travels 164th often as she comes and goes from her house nearby. The interchange is the first exit north of where I-5 and I-405 cross.

I-5 is under state Department of Transportation jurisdiction while 164th, at that location, is Snohomish County’s responsibility, so I posed the question to both.

“Traffic control devices on freeway entrances and exits are controlled by WSDOT, while the surrounding areas are controlled by a separate jurisdiction, such as a county or city,” said Dale Valliant, a traffic operations supervisor for the county. “The area where 164th Street SW crosses over I-5 is no different and has a high volume of vehicles.”

“It is a constant dance between flow on the corridor and on the freeway ramps. During non-rush hour times, traffic control experts still have to balance the capacity on 164th, the flow of traffic on the freeway and that of vehicles from other streets that feed into 164th,” he said.

Joseph Calabro, a spokesman for WSDOT, echoed Valliant.

“People traveling eastbound and westbound on 164th Street SW compete with those coming from and heading to the side streets. There is only so much a green light can do to mitigate overall congestion in the area. At this location, in particular, the combination of the Ash Way Park and Ride, multi-unit housing and nearby businesses contribute to the number of vehicles using the intersection,” he said.

Calabro also previewed an upcoming project for that location, the installation of an adaptive traffic signal, which could potentially ease congestion.

“The new signal, scheduled for construction in 2021, would prioritize directions of travel most in need of a green light in real time. It does so by analyzing traffic volumes approaching the light from each direction. This makes it especially productive during those off-peak hours when volumes are low.”

Sounds like Moberly isn’t the only one inching over the freeway on 164th.

Lizz Giordano: 425-374-4165; egiordano@heraldnet.com; Twitter: @lizzgior.

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