Diverging from the norm to deliver a diamond

Update: July 2025: Diamonds in the rough

The eight-day closure of State Route 18 July 17-25 will allow the switch to a diverging diamond at the interchange.

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By David Rasbach

Eight-day closure of SR 18 will build northern end of diverging diamond

They say diamonds are formed under pressure, and building the diverging diamond interchange at I-90 and SR 18 has been no exception. We know the closures, detours and delays have been tough. But all the time, planning and pressure has gone into shaping something that will last.

From July 17 to July 25, crews will complete the northern half of the diverging diamond interchange at I-90 and SR 18. This work requires another full closure of SR 18 in both directions at the I-90 interchange. It’s longer than the June closure because there’s more work to do, but when the road reopens on Friday morning, July 25, people will begin using the new diverging diamond configuration.

During an eight-day closure of SR 18 under the I-90 bridges, crews will build out the northern end of the new diverging diamond. When we reopen July 25, traffic will be shifted into the new configuration.   

SR 18 will be fully closed in both directions at the I-90 interchange. This closure will be in effect from 9 p.m. Thursday, July 17, through 5 a.m. Friday, July 25. No traffic will be allowed under the I-90 bridges during this time.

July 17-18 will include rolling slowdowns on I-90 and 10-minute traffic holds on SR 18 and Snoqualmie Parkway as crews stripe ramps and set the stage. As before, emergency responders will be allowed through the work zone. We’re working with freight partners to help them plan ahead and avoid using local roads as detour routes.

What’s happening during the closure?

Crews will complete a major phase of work on the northern part of the new interchange, including:

• Install drainage and electrical crossings
• Build concrete islands and curbing
• Set and program new traffic signals
• Tie in the new I-90 on-ramps
• Stripe lanes, install signs and switch to the new traffic pattern

This work compresses what would normally take months into a single week, minimizing long-term disruptions and lasting improvements to the corridor.

Detour and access information

While mainline I-90 will remain open, traffic using on- and off-ramps will be restricted:

• Eastbound I-90 off-ramp traffic can only turn right (south) onto westbound SR 18
• Westbound I-90 off-ramp traffic can only turn right (north) onto Snoqualmie Parkway
• No left turns will be allowed from either off-ramp
• Eastbound SR 18 traffic must detour via eastbound I-90 and loop around
• Southbound Snoqualmie Parkway traffic must detour via westbound I-90 and loop around

During the July 17-25 closure of SR 18, you can detour using eastbound and westbound I-90 and loop around at nearby interchanges – exit 20 (High Point Way) or exit 22 (Preston/Fall City) to the west of SR 18 or exit 27 (Southeast North Bend Way) east of SR 18 – to reach your destination.   

Maintaining access: Emergency responders will be allowed through the SR 18 work zone under the I-90 bridges during the closure.

Freight advisory: Freight haulers heading westbound on I-90 should plan ahead:

• Use Exit 22 (Preston/Fall City) to loop back to westbound SR 18
• Or continue west on I-90 to southbound I-405

Please do not use Snoqualmie or Issaquah city streets or Issaquah-Hobart Road. These streets are not suitable for semi-truck traffic.

Westbound I-90 freight traffic should either use exit 22 (Preston/Fall City) to loop back to SR 18 or continue on westbound I-90 to southbound I-405. Issaquah city streets and Issaquah-Hobart Road are not suitable for semi-trucks.   

Full detours will use:

• Exit 20 (High Point Way) or exit 22 (Preston-Fall City)
• Exit 27 (Southeast North Bend Way)

We expect delays, especially during peak travel times. Please plan ahead, leave early and consider alternate routes if possible. Real-time traffic updates are available via the WSDOT app and travel map.

People trying to reach Snoqualmie during the closure of SR 18 should use eastbound I-90, loop around to westbound I-90 at Southeast North Bend Way (exit) 27 and exit to SR 18/Snoqualmie Parkway.

During the closure of SR 18, people coming from Snoqualmie Pass will have to follow a detour to reach westbound SR 18, while people heading from eastbound SR 18 toward the pass can follow their normal route.

During the closure of SR 18, people coming from Snoqualmie and heading to Maple Valley or over Snoqualmie Pass will need to use westbound I-90 and loop around at the Preston or High Point interchanges.

During the closure of SR 18, people coming from south of the I-90/SR 18 interchange who need head west on I-90 will need to use eastbound I-90 and loop around at Southeast North Bend Way.

What’s next

Opening the diverging diamond marks a major milestone in the I-90/SR 18 interchange project.

Work still remains, as we’ll need to return in the next few weeks to add a top layer of asphalt throughout the diverging diamond, including the ramps. We’ll be back a few weeks after that for final lane striping. We’ll announce the details for that work once it’s finalized.

Though the diverging diamond will be open, it will not fully function as designed to allow traffic to flow until we complete widening SR 18 to two lanes in each direction south of I-90. The project will wrap up that work later this fall, and that’s when we expect you’ll see reduced congestion at this busy interchange. That’s when this diamond in the rough will be ready to shine.

Once complete later this summer, the new I-90/SR 18 diverging diamond interchange will improve traffic flow, reduce congestion and increase safety through one of the state’s busiest interchanges.

Preserving history: Saving a piece of the historic Puyallup River Bridge as demolition gets underway

By Kris Olsen

Say goodbye but plan for a “hello there!” to the historic, 100-year-old SR 167 Puyallup River Bridge. The bridge, sometimes called the Meridian Street Bridge, is going to be demolished beginning Wednesday, July 9. Well, most of it will be demolished, but we’re saving a piece for something special.

An important link
Built in 1925, the Puyallup River Bridge quickly became a vital link across the river, connecting the growing city of Puyallup to north Puyallup, Tacoma and beyond. It played a key role in the economic development of the area. The bridge helped people and goods move through the agricultural heart of Pierce County. Its construction went hand in hand with the region’s growth spurred by more cars and trucks and the popularity of the Washington State Fair, known then as the Puyallup Fair.

The Puyallup River Bridge not long after its construction in 1925.

Innovative design
Designed by the Union Bridge Company in Seattle, the bridge featured an innovative variation. It used steel truss that allowed for a longer span without requiring heavier materials in its construction. In recognition of its unique design, the 371-foot-long bridge was added to the National Register of Historic Places in 2014.

Time takes its toll
But the bridge suffered many of the indignities of old age with failing parts. Time and weather had taken its toll on the steel, the concrete deck and the piers. It was no longer structurally sound or safe. We needed a new bridge over the river.

Two big moves
In July 2014, we reinforced the bridge and then moved it upstream by 60 feet. It continued to carry northbound traffic over the river during construction of a new bridge. When the new bridge opened in 2015, it was time for the old bridge to be removed from over the river.

Moving a 378-ton bridge is no small task. Over a weekend in August 2016, teams specializing in complex moves jacked the bridge up 21 feet. Then they carefully shifted it onto moving dollies and slowly pulled it north on SR 161 to a spot on our right of way near the SR 167 interchange.

The Puyallup River Bridge is slowly pulled up North Meridian Avenue in August 2016 to its final resting spot near SR 167

Then we offered it for sale. We also offered $1 million to anyone who met the qualifications to relocate, preserve and maintain the bridge. Still, we didn’t receive any qualified proposals.

With that, the efforts to save the bridge came to an end. Ever since, it’s been sitting in our right of way. We developed plans to one day demolish the bridge as part of our SR 167 Completion Project. That day has now arrived. To make room for the SR 167 expressway, the bridge is going to be cut apart and the steel recycled.

The Puyallup River Bridge rests in WSDOT right of way, just off North Meridian Avenue, where it will be demolished.   

Saving a piece of history

Not all of it will be destroyed though. The Puyallup City Council asked us to save and restore a small section of it. That section will be placed on the future spuyaləpabš Trail near the SR 167/North Meridian interchange as a historical heritage marker.

A portion of the historic Puyallup River Bridge will be preserved along the spuyaləpabš Trail near the SR 167/North Meridian interchange.

The bridge may be going, going, gone, but it’s never going to be forgotten.

Saddle Up: “Wild West Weekend” rides into Puget Sound with THREE big closures

July 10, 2025 - UPDATE: The work on southbound SR 167 in Kent has been postponed to a later date, and all references to that work have been removed from the blog. The other projects mentioned in this blog are still happening as originally scheduled.

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Saddle up, Puget Sound – there's a highway showdown brewin' on all fronts. Dust is flyin', detours are comin' and a few of our rowdiest roads are fixin' to be wrangled.

This ain't your average construction weekend. It's a Wild (Pacific North)West showdown, and the only thing missin' is a tumbleweed.

Across Washington, we've got 117 projects under construction this season. But from July 11-14, all eyes are on a cluster of troublemakers right here in the central Sound: full closures on southbound I-405 in Kirkland, northbound I-405 in Renton, and southbound I-5 at the Convention Center in Seattle.

And just one week later, the most infamous outlaw of 'em all – Revive I-5 – rides into Seattle, shuttin' down northbound I-5 at the Ship Canal Bridge for the weekend of July 18-21 and kickin' off four weeks of lane reductions.

So, grab your map, chart an alternative course or saddle up a new horse (like KC Metro or Sound Transit) and keep an eye out, because the road crews are takin' the reins this weekend.

It’s a Wild West Weekend in central Puget Sound with three major closures wanted for disrupting travel.

Wild West Weekend's Most Wanted

WANTED: Southbound I-405 in Kirkland

ALIAS:  Buffalo BRT

Wanted for:  Occupying space meant for a transit-first interchange rebuild

What's goin' down:  As part of the NE 85th Street Interchange and inline BRT Station Project, crews will pave southbound I-405 as part of overall work to transform to better connected transit.

Closure details:  Southbound I-405 in Kirkland will be closed from Northeast 124th Street to Northeast 70th Place from 11 p.m. Friday, July 11 to 4 a.m. Monday, July 14

Ramp closures include:

• Northeast 116th Street on-ramp to southbound I-405
• Northeast 85th Street on-ramp to southbound I-405
• Southbound I-405 off-ramp to Northeast 85th Street

View detour map

Project information:  I-405/Northeast 85th Street Interchange and Inline BRT Station Project | WSDOT

WANTED: Northbound I-405 in Renton

ALIAS:  The Express Toll Lane Bandit

Wanted for:  Occupying space needed for future express toll lanes

What's goin' down:  As part of the I-405 Renton to Bellevue Widening and Express Toll Lanes project, crews are shifting lanes and rebuilding the roadway to prepare for a future with more capacity, better access and new toll lane connections. During this closure, crews are installing upgraded drainage systems, replacing overhead sign structures and swapping out pavement panels.

Closure details:  Northbound I-405 in Renton will be closed between SR 169 (exit 4) and Sunset Boulevard NE (exit 5) from 11:59 p.m. Friday, July 11 to 4 a.m. Monday, July 14

Ramp closures include:

• SR 169 on-ramp to northbound I-405
• Northbound I-405 off-ramp to Sunset Boulevard Northeast (Exit 5)
• The northbound SR 167 direct connector ramp to northbound I-405

View detour map

Project information:  I-405/Renton to Bellevue Widening and Express Toll Lanes Project

WANTED: Southbound I-5 at the Convention Center

ALIAS:  The High Pressure Kid

Wanted for:  Givin' fire systems under the Convention Center a midnight wakeup call

What's goin' down:  WSDOT maintenance crews are ridin' in overnight to test the fire suppression system beneath Seattle's Convention Center. It's a quick mission to keep our tunnel infrastructure safe and ready.

Closure details:  Southbound I-5 in Seattle will be closed from the Stewart Street off-ramp to the Spring Street on-ramp from 11 p.m. Friday, July 11, to 6 a.m. Saturday, July 12.

Ramp closures include: 

• Eastbound Mercer Street on-ramp
• Yale Avenue/Howell Street on-ramp
• Union Street off-ramp
• James Street off-ramp

Detour:  The Express Lanes will run southbound during this closure.

ACCOMPLISES:

• Westbound I-90 off-ramp to SB Rainier Ave S: Closed 9 a.m. Friday, July 11, to 5 a.m. Monday, July 14, for SDOT pedestrian safety upgrades.
•  For more information www.seattle.gov
• Northbound I-5 off-ramp to NE 130th St: Closed starting 10 p.m. Friday, July 11, until late July for Sound Transit Lynnwood Link construction
• Eastbound NE 130th Street over I-5: Closed until Aug. 25
• For more information www.soundtransit.org

Highway Showdown Survival Guide

Even if it isn't your first rodeo, plan ahead for a full-scale, multi-corridor roundup across the region with closures and detours. Whether you're ridin' solo or hauling a whole wagon train, you'll want to be ready before you head out. Here's how to stay one step ahead:

• Scout the terrain: Check WSDOT's real-time traffic map, mobile app, or social media before you ride out. A smart traveler knows what's ahead.
• Pick your moment: Avoid the rush. Leave early, return late, and give yourself time for the long way 'round.
• Know your back-up route: Review signed detours and alternate trails before you saddle up.
• Follow the front line: Flaggers, signage, and law enforcement are out there helping keep order and guiding the herd. Tip your hat and follow their lead.
• Switch saddles if needed: Transit, carpools, and HOV lanes might be the quicker horse for this ride.

Til We Ride Again, Pardner

Closures come and go, but the job's bigger than one weekend. Next week, we ride again. Northbound I-5 at the Ship Canal Bridge will fully close from July 18-21 and then reopen with four weeks of lane reductions while we work to preserve this valuable corridor. We're laying the groundwork for stronger roads and smoother rides downline.

Out here on the asphalt frontier, it's not the fastest rider who gets through, it's the one who knows the trail, reads the signs and plans their route.

Turn and face the change: Big changes coming to the South 188th Street/SR 509 interchange in south King County

We may have rounded the corner to summer and can finally (hopefully?) put away our raincoats and puffy jackets until fall. But there are bigger changes than the seasons coming to the South 188th Street/State Route 509 interchange as part of the SR 509 Completion Project in south King County.

Upcoming changes to SR 509 Interchange

Scheduled to begin Monday, July 7, crews will change the SR 509 ramps to and from eastbound South 188th Street/Des Moines Memorial Drive South and install a new traffic signal. Drivers will use the new traffic signal to:

• Enter northbound SR 509 from both directions of South 188th Street/Des Moines Memorial Drive South.
• Exit southbound SR 509 to eastbound South 188th Street/Des Moines Memorial Drive South.

People driving from southbound SR 509 to westbound South 188th Street/Des Moines Memorial Drive South will continue to use the existing off-ramp. This change will be in place for the next two years.

Starting July 7, crews will change the SR 509 ramps to and from eastbound South 188th Street/Des Moines Memorial Drive South. 

Changes necessary for safety and efficiency

These changes to the SR 509 and South 188th Street/Des Moines Memorial Drive interchange are a key step toward building the new SR 509 Expressway between South 188th Street and 24th Avenue South. This work is important to make the construction area safer and more efficient for our crews. Once this section of the expressway is complete, we’ll begin major upgrades to the interchange, including new roundabouts and a multi-use path that will link directly to King County’s Lake to Sound Trail.

If you live near, work near, or travel through this area, expect noise and dust typically associated with road construction. Trying to reach local businesses? Don’t worry, we’ll make sure you can still get there.

Short-term inconvenience for long-term benefits

We know traffic changes are a hassle, but we promise the short-term inconvenience will pay off in big ways down the road (pun intended). Once complete, the improvements to the South 188th Street interchange and the new SR 509 Expressway will reduce congestion, streamline traffic flow, and boost safety in the area, making it easier for everyone to get around.

This is all part of the larger SR 509 Completion Project, which:

• builds a new four-lane expressway between Interstate 5 and SR 509's current end near Sea-Tac Airport
• builds new I-5 ramps
• improves I-5 interchanges in south King County
• constructs new bridges

When the entire SR 509 Completion Project is done, it will create an important north-south alternative to the congested I-5 corridor between Seattle and south King County. The future is bright!

New interchange improves access

When all is said and done, the new SR 509/South 188th Street interchange will let people travel in all directions, improving access for everyone—whether you’re heading north, south, east or west. The design will include roundabouts, which are safer and more efficient than traditional intersections. Plus, for those heading south on SR 509, the South 188th Street interchange will be the last exit before the expressway’s tolled section.

When the SR 509/South 188th interchange work is completed, people will be able to travel in all directions with improved access whether you drive, walk, ride or roll through the area.

Why roundabouts?

Because they work—and they work well. Our interchanges are designed to be safer for all road users, including drivers, pedestrians, and cyclists. Roundabouts help slow down traffic, provide safer crosswalks, and reduce the chances of dangerous collisions. They also keep traffic moving smoothly and efficiently, even as volumes increase.

For this project, we ran traffic studies and simulations to determine the safest and most effective design. The roundabouts came out on top, outshining other options, especially when we factored in large vehicles like trucks and buses, as well as non-motorized users.

Roundabouts are already working wonders at over 100 locations across Washington State. We’ll continue share information roundabout safety, so everyone feels confident navigating them once construction is complete.

Have questions or want more information?

We know that change brings questions, and we’re here for them! Send us an email at sr509construction@wsdot.wa.gov or give our 24/7 construction hotline a call at 206-225-0674.

Want to stay updated? Sign up for our project listserv to get the latest news and updates straight to your inbox.

Thanks for your patience as we work to make this important project a reality. We’re excited for the positive changes that lie ahead!

Streaming soon under US 101: Season 3 of major fish passage construction on the Olympic Peninsula

By Angela Cochran

It may not be the show you’ve been waiting for the past several years (looking at you, Stranger Things!), but it’s sure to be the talk of the town for summer travelers on the Olympic Peninsula.

With eight new episodes – uh, we mean work zones – it’s lights, camera, action – ok, well it’s just lights. Red, yellow and green ones. Traffic lights, to be specific. But don’t worry! They are all temporary.

You’ll see a lot of these guys if you’re traveling US 101 along the coast this summer.

If your summer plans include taking the “loop” (US 101 on the Olympic Peninsula), you’ll want to include some extra travel time. But we’ll keep you moving through the work zones.

This is the third season of our “Coastal 29” project. The work removes barriers to fish at 29 locations under US 101 and State Route 109.

All of the fish passage locations that are part of the Coastal 29 project.

We reached the halfway point for the project last fall after completing work at five locations under SR 109 near Ocean Shores and four locations under US 101 south of Forks. This summer, we’re getting US 101 ready for its closeup.

Bonus episode

In addition to the fish passage sites, we have a ninth location where US 101 is reduced to one lane of alternating traffic. This is due to erosion along the highway near Kalaloch. In the next several weeks, our contractor will work to repair the hillside and reopen both lanes.

Plot summary

The temporary changes will remain in place at the eight fish passage work zones through the end of the year. The changes include a temporary bypass road. Most of the locations already have traffic on bypass roads. These locations all have one-way alternating traffic around the clock. The bypass roads will open at the remaining locations within the next couple of weeks.

Aerial image of a bypass road with a temporary bridge. 

Once traffic is shifted onto the bypass road at each location, crews will start digging up the highway and relocating aquatic life in the stream. Before stream work begins, we temporarily divert the stream. This happens during a time when fish are less active in the stream. We call this the “fish window”. This window varies by location. For these streams, it starts in July.

Up next

After the Independence Day holiday, we will block off the project area with fencing and move fish and other species up or down stream of the project. We also document the number and types of species found in the stream during this time. A pipe is then used to divert the stream around the project area, which gives crews the room they need to rebuild the stream bed. Once that work is complete, tree trunks and native plants are added for shelter and nutrients. In addition to the stream work, we build the new structure.

Fish passage work includes relocating aquatic life before working in the stream.

Main character arc

One of the projects just hit a big milestone. We placed girders, or large support beams, on the new bridge over May Creek. This project is located at the Jefferson/Clallam county line south of Forks. Girders act as the backbone of a bridge. They are placed on top of the piers and support the driving surface. The new May Creek bridge has five girders that are each 175 feet long – the size of the Seattle Ferris Wheel!

Now that the girders are in place, we are working on the bridge deck. The contractor expects to finish most of the bridge work and open it by the end of this year. If this happens, they will pause work for winter and perform stream work when the fish window opens in summer 2026. We expect to complete the whole project in fall 2026.

Next season on Coastal 29

All bingeworthy series come to an end. By the end of this year, we will have removed barriers to fish at 22 locations under US 101 and SR 109. It’s been blockbuster work since 2023.

That means our construction series finale will be a little shorter. We’ll only have seven culverts left to replace along the coast in 2026 and 2027. Crews will finish work at the two sites under US 101 near Forks next summer. We will also replace culverts under SR 109 at five locations to complete this massive endeavor.

As always, you can tune in for live traffic information on our app and statewide travel map.

It’s rewarding work removing barriers to fish. You could call it a rerun (but, you know, with fish).

Two local roads in SeaTac close to make way for the new SR 509 Expressway

South 194th Street connection to Des Moines Memorial Drive South will close permanently on July 7. South 192nd Street is scheduled to close for nine months also on July 7

The long-awaited State Route 509 Expressway in south King County is taking shape. Before travelers can move without stopping between South 188th Street and I-5, our construction crews have a lot of work ahead of them at South 192nd and South 194th streets near Des Moines Memorial Drive in SeaTac.

South 194th Street is closing for good

First up: On July 7 crews will permanently close the South 194th Street connection to Des Moines Memorial Drive South. This is because the new expressway is going to be built right where the current intersection is located.

Building the new South 192nd Street bridge

Shortly after South 194th Street is closed, crews will shut down a portion of South 192nd Street for nine months while they build one of five new bridges for the expressway. It’ll be closed just west of Des Moines Memorial Drive.

Right now, South 192nd Street is just a road, but it will become a bridge. The new SR 509 Expressway will go under South 192nd Street. To build the expressway, crews need to dig out the road and transform it into a bridge. South 192nd Street, between Des Moines Memorial Drive South and Eighth Avenue South, will be closed for about nine months starting July 7.

The new South 192nd Street bridge will better serve the needs of the community with wide, ADA-accessible sidewalks.

The new South 192nd Street bridge will better serve the needs of the community with wide, ADA-accessible sidewalks.

Originally, crews planned to build the new bridge before permanently closing the South 194th Street connection to Des Moines Memorial Drive. But closing both at the same time results in:

• Safer detour routes with fewer tricky left turns.
• Keeping Des Moines Memorial Drive South open more often.
• Less dust and dirt from construction vehicles.
• Trucks having the ability to travel during the day instead of at night.

Getting around during construction

While South 192nd Street is closed:

• Cars will be detoured to South 188th Street or South 200th Street using Eighth Avenue South and Des Moines Memorial Drive South.
• Large trucks should use First Avenue South to avoid tight turns at Eighth Avenue South.

If you live or work nearby:

• Driveway access on South 192nd Street will be maintained.
• Expect noise, dust, and vibration during regular work hours (weekdays, 7 a.m. to 5 p.m.)
• Some night work may be necessary (weekdays, 8 p.m. to 6 a.m.).

If you commute through the area:

• Use extra caution through the work area and detour route and expect delays.

If you use the Lake to Sound Trail:

• Expect closures and detours during bridge. construction. Visit our project webpage for updates.

The new South 192nd Street bridge over the future SR 509 Expressway is scheduled to open in early 2026.

Project background

The SR 509 Completion Project in King County is part of the Puget Sound Gateway Program, which also includes the SR 167 Completion Project in Pierce County. Together, these projects complete two of the Puget Sound region’s most critical freight corridors and improve access to I-5, the ports of Tacoma and Seattle, and Seattle-Tacoma International Airport. The SR 509 Completion Project builds a new four-lane expressway between I-5 and SR 509's current end near Sea-Tac Airport, builds new I-5 ramps, improves I-5 interchanges in south King County, and constructs new bridges. When complete, the project will create an important north-south alternative to the congested I-5 corridor between Seattle and south King County.

Keep in touch

The best way to stay up to date on the SR 509 completion project is to sign up for our listserv. Questions? Send us an email at sr509construction@wsdot.wa.gov or give our 24/7 construction hotline a call at 206-225-0674.