Crash history limits left turns at Mill Creek traffic signal

Drivers winding their way along 35th Avenue SE to Seattle Hill Road come to an intersection managed by traffic signals.

At the intersection, each side of 35th has the same approach: a bike lane, a vehicle lane to go straight, and turns lane left and right.

But left turns are treated differently by the signal depending on if you’re heading east or west to Seattle Hill Road.

Travelers going south on 35th and turning left to eastbound Seattle Hill Road get a solid green arrow that phases to a flashing yellow arrow before turning solid red. But anyone heading north on 35th hoping to turn left onto westbound Seattle Hill Road only gets a solid green arrow then solid red.

It has perplexed nearby Bothell resident Corey Smith.

“I regularly sit at the light while those across from me are able to turn,” Smith told The Daily Herald. “There doesn’t seem to be any line-of-sight issues (and I) would like to know the logic there.”

The intersection straddles the border of Mill Creek city limits and unincorporated Snohomish County. Seattle Hill Road east of 35th is the county’s jurisdiction, and west is the city’s.

Both agencies share the traffic signals’ operations, Mill Creek spokesperson Scott Harder said.

But the county led the signal phasing change that stalls Smith at the intersection.

Snohomish County Public Works adjusted the signal in 2019 because of an increase in crashes involving drivers going north on 35th and turning left onto Seattle Hill Road, county traffic engineer Mohammad Uddin wrote in an email.

There were several crashes at and near the intersection between 2015 and 2018, according to data from the Washington State Department of Transportation.

Before the change, the signal had a green arrow that phased to a flashing yellow arrow from northbound 35th to westbound Seattle Hill Road.

“We identified a sight distance/visibility issue for this movement,” Uddin wrote. “To address this issue, the signal phasing was changed to only allow protected left turns for that movement. Southbound traffic on 35th Avenue SE turning east onto Seattle Hill Road does not have a visibility/sight distance issue.”

The geometry of the intersection contributes to the visibility problem, Uddin said. The north-south road of 35th meets the intersection at a skewed angle, which can confuse drivers.

That pushed the county to scrap the flashing yellow arrow at northbound 35th. But it “adequately” adjusted timing at the signal, Uddin said.

The county isn’t likely to allow for those permitted left turns — as opposed to turns protected by a solid green arrow — at different times of day with lower traffic volumes, either.

“During peak hours due to traffic congestion, vehicles travel at lower speed but during the off-peak hours speed is higher resulting in a higher risk for severity of collision,” Uddin wrote. “During off-peak hours, northbound left turns have adequate green time to clear all vehicles that would wait to make left turns.”

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