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Construction began this week on 120th Street extension in Kirkland
The average wait for a car stopped at the intersection of Northeast 116th Street and 124th Avenue Northeast lasts a minute and 23 seconds. That, according to the city of Kirkland’s transportation policies, is nearing failure.
But it could get worse. To understand how much worse, transportation engineers from the city of Kirkland created a model more than a decade ago to calculate what the wait time would be at the same intersection in the year 2022. The average wait time, the engineers discovered, would quadruple—to more than four minutes.
“That’s total failure,” said Thang Nguyen, the Kirkland transportation engineer responsible for measuring the traffic impacts of development.
The solution is to build a new road extension that will connect Northeast 120th Street to 124th Avenue Northeast. Construction on that road began Feb. 24 and will be finished by the end of this year.
Aside from providing a more direct option for drivers heading to the freeway from 132nd Avenue Northeast, as well as drivers heading east to the Lake Washington Institute of Technology, the new road extension will ease pressure primarily at four nearby intersections and cut their average wait times in half, from a combined nine and a half minutes to a combined four and a half minutes.
And it’ll do it by reducing the number of ‘competing movements’ commuters face at the four intersections.
“‘Competing movements’ are movements that are competing for green time at the intersection,” said Nguyen. “Let’s take a left turn and through-movement. They are competing movements. Those are movements that cannot run at the same time. One has to wait for the other through signal phasing in order to get through the intersection. This road will reduce those competing movements at each intersection.”
The result for drivers is less time in traffic.
At the intersection of 124th Avenue Northeast and Northeast 124th Street, for example, the road extension will cut 50 seconds from the 140-second wait traffic engineers expect by the year 2022. The biggest beneficiary is the intersection of 116th Street and 124th Avenue, where traffic would be waiting for more than four minutes on average—if not for the road extension. That’s three times longer than the current wait.
The Northeast 120th Street road extension cuts more than three minutes from that, however. That means traffic will sit at that intersection for 17 seconds less in 2022 after the new road exists than it does now in 2014 before the road exists.
Through annexation, Kirkland has added more than 200 lane-miles to its street network. But this will be the first new road the city of Kirkland has added through road construction since 1993, when the city built the missing piece of North Rose Hill’s 100th Street, which provided a continuous link from 124th Avenue to 132nd Avenue.
Constructing the Northeast 120th Street extension will require seven-and-a-half months, starting late this winter. But the city of Kirkland has been planning for these 880 feet of additional roadway since 1997. It’s been working on the design and property acquisitions since 2007.
“It involved reaching out to the property owners to purchase right of way,” said Rod Steitzer, the supervisor of Kirkland’s Capital Improvement Program. “There are four parcels on this roadway. Three to the north. One to the south.
And on that right of way, city engineers have already solved several engineering challenges. One challenge was how to build a road that gradually descends from its intersection with Slater Avenue without consuming portions of the Frontier property to the north and the Infiniti of Kirkland dealership property to the south.
The answer: 15-foot retaining walls.
“It’ll look like modular block style wall,” Steitzer says. “It’ll change the elevation, the grade so the slope is more gentle.”
Another riddle is what to do with all the stormwater. Without mitigation, the new street would shed nearly 900,000 gallons of storm water in an average year of Kirkland precipitation. That’s enough to fill Peter Kirk Pool four and a half times. Most of that water would almost certainly drain toward the area’s lowest point, Totem Lake, which is already vulnerable to flooding.
The answer: “We’re using a vault, which takes water from the roadway and any water coming into the adjacent roadway,” Steitzer said. “The vault collects that water and releases it at a slower rate so we don’t have flooding in Totem Lake.”
That vault can hold 270,000 gallons of stormwater, or 50,000 more gallons than Peter Kirk Pool.