SR 18 Tiger Mountain closure on July 23 allows WSDOT teams to combine efforts

Maintenance and engineering work for future widening and interchange projects will occur simultaneously

SNOQUALMIE – Drilling, measuring, surveying, inspecting, paving and mowing are just some of the many tasks on the to-do list during a full closure of State Route 18 on Saturday, July 23. Both directions of the highway between Interstate 90 and Issaquah-Hobart Road are scheduled to be closed from 6 a.m. to 8 p.m.

During the closure, WSDOT maintenance crews and engineering teams from the SR 18 Issaquah-Hobart Road to Deep Creek widening and the I-90/SR 18 interchange improvement projects will work in multiple areas. Coordinating schedules and advance planning allows all three groups to accomplish tasks in a single daylong closure, reducing the cost of traffic control and inconvenience to highway users.

Closure information

  • 6 a.m. to 8 p.m. Saturday, July 23.
  • Westbound SR 18 closed at the I-90 interchange in Snoqualmie. Local access only is allowed for residents to reach Southeast 104th Street. 
  • Eastbound SR 18 closed at Issaquah-Hobart Road.
  • The ramp from Issaquah-Hobart Road to eastbound SR 18 will be closed.

Know before you go

Highway users should plan to allow extra time and use alternate routes to reach their destinations.

SR 18 maintenance work

Paving crews will repair failing pavement and fill potholes, primarily in the eastbound lanes. They also plan to work on highway drainage, guardrail repairs, and cut back brush and tall grass to improve highway sight lines in both directions of the highway.

SR 18 widening design work

The engineering project team is taking advantage of the closure to gather information and data for the planned widening of the highway. One team will drill through asphalt to gather samples while others will take highway measurements, perform survey work and collect information needed for the state and federal permits required before the highway is widened.

The $665.9 million widening project received $639.9 million in the 2022 Move Ahead Washington transportation program to complete design and construction. A widened SR 18 will feature:

  • Two lanes in each direction between Issaquah-Hobart Road and Deep Creek.
  • Right-in, right-out access at the Tiger Mountain summit.
  • Roundabouts at the Issaquah-Hobart Road interchange.
  • A median barrier the length of the corridor.
  • Seventeen new bridges and more than 60 retaining walls.
  • Eleven fish passage improvements and multiple wildlife crossings.

The construction schedule has not been determined, but the earliest construction work could begin is 2025 with completion in 2029.

I-90/SR 18 interchange improvement work

Contractor crews for the interchange improvement project will also be on site performing pavement inspections, reviewing conditions of existing bridges and survey work.

In January, WSDOT selected Aecon Pacific Northwest, Inc. as the general contractor to build a new diverging diamond interchange. Crews will also widen SR 18 to two lanes in each direction between the interchange and Deep Creek. These improvements will help improve traffic flow at one of the busiest interchanges in the state.

The $190 million project is scheduled for completion in 2025.

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Improved access to 98.2 miles of upstream fish habitat

through 15 fish passage projects in 2021.

28% increase in the value of exports and imports 

from $90.2 billion in 2020 to $115.5 billion in 2021.