I-90 Trail
Construction on the I-90 Trail is underway. The trail will be closed in segments. Sign up for updates to learn more.
This StoryMap focuses on the I-90 Trail. To learn more about the Mercer Enatai Sewer Upgrade project as a whole, visit the project website.
The blue line on the map shows the new sewer pipeline. King County is also upgrading the North Mercer Pump Station and the City of Mercer Island's Lift Station 11.
What are we building?
King County is installing approximately four miles of new sewer pipe across north Mercer Island and Southwest Bellevue. Some of the new pipe will be installed underneath the I-90 Trail on Mercer Island. Work will have an impact on everyone who lives near or travels on the trail.
This image shows the new pipeline in light green where it will be installed under the I-90 Trail.
What to expect
Construction is disruptive.
Everyone who lives near or travels on the I-90 trail across Mercer Island will be impacted by the work.
We will send out alerts so you can plan ahead if you live near the active work area.
Open cut trenching
Crews will use a construction technique called “open-cut” trenching to bury the pipe where it needs to go. During open-cut construction, crews dig from the surface to the pipe depth. Then they lay the pipe, cover it and restore the surface.
Open cut construction video shows you what to expect
This image shows a trench box holding back soil so workers can install pipes. On the I-90 trail, the trench width will vary between 8 and 30 feet wide.
Construction inconveniences
Like any construction project, there will be noise, dust, traffic impacts and other inconveniences.
- Permitted weekday work hours are 7 a.m. to 7 p.m. We will provide advance notification of any weekend or after hours work.
- Bicycle and pedestrian traffic will be detoured off the I-90 trail.
- The detour routes merge bicycles and cars along North Mercer Way.
- Pedestrians will be on a separated path.
Detour routes will have sharrows, which are painted marks on the road that remind drivers to look out for bicycles.
Work done in sections
We expect work on Mercer Island to take place in sections up to 1,000 feet long.
Sections where construction is underway will be closed for approximately six months at a time.
Trenches will be covered with steel plates at the end of the work day but public safety requires that each in-progress section remain closed to public access around the clock. We will not be able to open a work section until new pavement has been laid on top of the refilled trenches.
We are only permitted to close one section at a time.
--> Construction schedules often change. Please sign up for our email list for this section of the project to stay up to date on timing and duration of the work.
Landscaping
Vegetation, including trees, bushes, and shrubs will be removed inside the work area.
Learn about restoration in the "When we're done section"
Schedule and duration
Construction on the overall sewer upgrade is underway and will last into 2025.
The I-90 trail will be closed in sections. We will post detours where trails are closed.
We will provide a more detailed schedule, including construction sections and schedules, on our website and through our email list once it is available.
Construction schedules often change. Please sign up for the email list about this section of the project to receive the most up to date information as it becomes available.
Detour routes
The I-90 trail will be closed while construction is underway.
What to expect:
- The primary detour route for pedestrians will be a separated 5 foot wide path on the north side of North Mercer Way.
- Bicycles will have two choices: dismount and walk the pedestrian path or merge with vehicles on the detour routes.
- Speed limits will be reduced to 20 MPH in the construction area.
- Sharrow markings will be added to the pavement. A sharrow is a marking on a road that reminds motorists that bikers are often present on the road.
The image shows the detour route during construction on the I-90 trail between Island Crest Way and Shorewood Drive.
I-90 Trail closures may shift slightly depending on where crews are working along that section.
Watch for detour route signage.
This image shows the detour route during construction on the I-90 trail between Shorewood Drive and SE 35th St.
Follow the blue route if you are biking or walking from Shorewood Drive to reach the eastbound I-90 Trail.
This image shows the detour route during construction on the I-90 Trail between SE 35th Street and SE 35th Place.
The detour route for bicycles merges bicycles with vehicles.
The pedestrian detour follows sidewalks and crosswalks along North Mercer Way, SE 36th Street, and East Mercer Way.
What you'll see when the work is done
King County will repave and widen the I-90 Trail.
When construction is complete, we will restore disturbed areas according to permit conditions agreed upon with the City of Mercer Island and Washington State Department of Transportation.
The I-90 Trail will be widened to meet multi-use trail standards. Where possible, the trail will be 12 feet wide with 2 feet of gravel on either side.
This conceptual image shows what the I-90 trail may look like after three years of plant and tree growth.
During work, crews will remove trees within the work zones. We will plant new trees at the end of the project. Many of the new trees will be planted in areas where trees are removed, but this is not always possible due to the widening of the I-90 trail. We will plant additional trees in areas near the project that currently lack tree canopy so that we leave behind more trees than we removed.
How to reach us
We are committed to working with you during construction.
Here is what you can expect:
- Flyer boxes along the trail with construction updates.
- Regular web updates.
- Email announcements. Sign up for the I-90 Trail list on our website .
- Quick resolution of problems and concerns.
- Call or email us . We will get back to you within one business if it is not an emergency. If it is a project-related emergency, we will get back to you right away.
Talk to us!
For more information or to schedule a virtual meeting, contact the Community Relations Team:
- 425-305-3578
- NMEsewer@kingcounty.gov
Learn more
Visit the project webpage to learn more and sign up for email and/or text alerts: www.kingcounty.gov/MercerEnataiSewer
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