I-90/SR 18 interchange project costs increase, state changes weigh station site, SR 18 lane expansion to trim budget

There are some potential changes to the I-90/SR Interchange Improvement Project – mostly driven by budget constraints.

Let’s start with some good news, though. Some city officials had feared the passage of Tim Eyman’s I-976 last November could delay the interchange project, but according to Snoqualmie Mayor Larson, it hasn’t.

The project was allotted a $150 million budget from the 2015 Connecting Washington transportation program, but most recent cost estimates pushed the project to approximately $196 million, according to 5th District Senator Mark Mullet.

Mullet said the majority of the increase stems from [fish] culvert requirements in the environmentally sensitive area surrounding the interchange and SR 18 area.

To reduce the budget, Mullet said the state trimmed costs related to the relocation of the former interchange weigh station by opting to site a smaller truck inspection station on eastbound I-90 near exit 42 and adding a small chain up enforcement area near exit 45. The state had been exploring placing the new weigh station near milepost 80 in the Cle Elum area.

Senator Mullet said there are also plans to add a small Washington State Patrol Commercial Enforcement outpost near North Bend, exit 34, to help with the new enforcement areas.

The second cost savings came from reducing the SR 18 lane expansion to the Raging River, instead of Deep Creek. WSDOT’s 90/18 interchange improvement project page currently says the project would also “widen nearly 1.5 miles of SR 18 to four lanes from the interchange to Deep Creek.” With this proposed change, SR 18 between Raging River and Deep Creek (approximately .75 miles) would reduce from 4 lanes to two. Just after Deep Creek, westbound SR 18 transitions back to two lanes over the Tiger Mountain summit.

Full SR 18 lane expansion still state transportation priority

Local residents and SR 18 commuters have been asking the state for years to widen SR 18 from I-90 to Tiger Mountain as this stretch of roadway – some of it just two lanes with no cement barriers and some covering steep, winding terrain – is very dangerous and known for head-on collisions.

Mullet explained the full SR 18 lane expansion – all the way to Tiger Mountain – is still a top, ongoing state transportation effort, but the first portion of the project – interchange re-design and first section of SR 18 lane expansion – is what is currently funded and is the budget they are working with.

He said the 2021 Washington State Legislative Session is when they are hoping to fully fund the entire $300 million project that, when completed, would improve the interchange and expand SR 18 to four lanes over Tiger Mountain. A new two-year transportation budget will be hammered out during that 2021 legislative session.

The 2019 two-year state transportation budget included $27 million for the engineering/planning to widen SR 18 from the Deep Creek area to Tiger Mountain.  That funding was allocated over four years, with the goal to make the full SR 18 widening project ‘shovel ready.’ 

Last May Senator Mullet said that the state would not be spending millions on engineering work for the SR 18 widening project unless it was considered a top transportation priority and planned to complete it. 

That engineering work is expected to be done by 2023 – right as the 90/18 interchange work is projected to finish, meaning the full widening phase could seamlessly begin.

According to WSDOT, 90/18 interchange construction is tentatively scheduled to begin in 2021 and the new diverging diamond interchange should open in 2023. The SR 18 lane expansion part of the project begins once the interchange work is finished.

Two-lane Raging River Bridge area of SR 18 near Snoqualmie. PC: WSDOT

Comments are closed.


    1. It is about .75 miles west of Deep Creek. SR 18 is a two-lane bridge over Raging River and Deep Creek I believe.

    2. If you are westbound on 18 (SW, really) heading up Tiger Mtn, Deep Creek is just a little further after the Raging River. You can see it on Google Maps.

      1. ah, i see it now. i don’t think it shows on bing maps which i was looking at.
        unfortunate that the 4 lanes will stop at the bridge–although getting the extra lanes to that point will help.

  • Just the widening of hwy 18 to the bridge would give the traffic at the I90 interchange somewhere to go. It’s WDOT stupid to do the interchange 1st, with the widening done it would ease congestion during construction of the interchange……30yrs in road construction, I know WDOT stupid when I see it.

  • IT’s laughable to say this is a “priority” for the state. If it was a priority it would have been done already. To add to the insult, a diverging diamond at the I-90/SR18 interchange is a terrible way to deal with the traffic issues at that point. First off, who in their right mind thinks that crossing traffic into oncoming lanes, then back again will make this a safer solution? Secondly, this model will only work if everyone strictly obeys the traffic laws and no one blocks the crossover sections. Do you really believe that will happen? It’s been proven for more than a decade that SR18 in this area is a death trap. It has a reputation for “taking your life in your hands” for travelers that use it on a daily basis and yet the state continued to do nothing. For more than two years there have been sections of the road surface at the bottom of Tiger Mt heading west that are in extreme disrepair and the best the state was able to do it put up a sign stating “Rough Road”. That tells you the “priority” that this road has with DOT. If it doesn’t directly impact Seattle, it is not a priority… no matter what a politician tries to sell you.

    1. Charles. It’s obviously a priority otherwise the funds wouldn’t have been earmarked for this, probably four years ago like most capital projects. WSDOT just spent $31M in Lacey as part of a greater $250M+ project to expand JBLM. I’ve traveled SR18 frequently for work and I am happy to see some improvement. Now I commute I5 to and from JBLM to Olympia everyday. I’m happy to see the investment here as well. You should just be happy your lawmakers are using the taxes to invest in capital versus blowing it like most states do. Stop complaining.

  • Living Snoqualmie