I-90 - SR 18 Interchange Improvements

Beginning in 2022, a new diverging diamond interchange will start taking shape at the existing I-90/SR 18 interchange near Snoqualmie, WA. This video explains why the new interchange is needed, how it will improve mobility and safety, and how to navigate it. The I-90/SR 18 diverging diamond interchange will be the second one built in the state. The project will also widen SR 18 to Deep Creek. The interchange and widening is scheduled for completion in 2025. You can read more about these improvements on the I-90/SR 18 interchange improvements project website: wsdot.wa.gov/Projects/I90/SR1...

[@NorthWoodsVideo]

I know this interchange well on trips to Spokane and North Idaho. Richard Gillette, you did an outstanding job creating this video for WSDOT!

[@kiwimumeeeeeeee]

Very excited to see this happen! I drive it twice a day.

[@derekpine5686]

As long as it doesn't take an hour to get through that interchange, I'll be happy.

[@seabeejb]

I've been a fan of diverging diamonds since the one in Springfield Missouri showed up. I'm glad to see they are making they're way here. Now if only we can elevate pedestrian traffic and keep them away from vehicular traffic. Both in diverging diamonds and large roundabouts.

[@allenslucher8555]

GREAT news!! :)

[@markbrinton6815]

I used the one at Marvin rd... It was really great. Flows really well.

[@jefffinkbonner9551]

Definitely vital to improve this corridor. It's the main truck route over the pass to the Port of Tacoma. Will this make SR 18 2 lanes in each direction all the way to Covington, or will there still be 1-lane sections south of Tiger Mountain??

[@winfredseymour4614]

This should be a vast improvement in safely navigating the interchange. It would be great if WSDOT could figure out a way to keep the high overhead lights working throughout the interchange. There are probably 12 to 15 high light poles in the interchange and they are most often dark. That is a big safety issue as well, particularly if drivers are not familiar with the area.

[@FlyingTigress]

Just so that you know, there's one here in Alaska. Muldoon Road at Glenn Highway

[@Vancovermycity]

Love this project approved and being started as well as your great content. Please also start paving i5 Seattle to Marysville as i5 has gotten to many pot holes 🕳

[@wsdot]

Paving I-5 through Seattle is part of the Revive I-5 project. Paving north will also be happening in stages: wsdot.wa.gov/projects/i5/revive/home

[@Themrine2013]

What about paving south? Going from Seattle to fife is a nightmare since most of that hasn't been repaved in decades.

[@jam2365]

​@Themrine2013 even going north. When you can see the rebar in some sections, it's time for some repair.

[@scarpia519]

Impressive, the gov actually spending money wisely to help the public. SR-18 is stop and go these days in that section.

[@deathhawk81]

WSDOT must have been playing some City Skylines and listening to Biffa :D

[@gavy7746]

Great that is being "improved", but improvement is always subjective. Call it what it is, a capacity increase, or lane additions.

[@ddog454]

Wa drivers can’t keep right unless passing, can’t comprehend a roundabout, good luck trying to get people to wrap their heads around this.

[@ikurasake]

Can we get a good amount of large-form native trees in the barrier areas and surroundings? Would support climate goals, mitigate environmental impacts of the freeway and make for efficient use of space. Not to mention it'd be more beautiful

[@chevelleguns92]

The entire area is literally cut through mountains 🤦‍♂️ literally all you see both sides is trees

[@ikurasake]

@@chevelleguns92 you'll be glad in 20 years if large trees are planted for this project, given the rate of canopy loss now

[@chevelleguns92]

You have to remove trees to widen this area🤦‍♂️ the roads now are so close to the forest there is barely room to pull off the side

[@miles5600]

And will you maintain its quality? Like actually filling up pot holes and repaving if needed?

[@Daren_PNW]

Thanks for the updates - what's up with the super bumpy and loud expansion joints on I-5 SB in Seattle SoDo?

[@wsdot]

It's part of the Revive I-5 project going on. We've worked a couple of weekends so far and will be back out the weekend of Sept. 11 to do more expansion joint work, which should help smooth out those areas.

[@Daren_PNW]

@@wsdot Ok, thank you. So we'll have to put up with loud bumpy joints all over that area for 3 more weeks?

[@compdude100]

@@wsdot Glad to hear that. Those expansion joints are really bumpy now!

[@jeremiahcromie9599]

While it will help. Should have added a 3rd lane going SB.

[@drewconway7135]

2:26 That’s a front-end collision right there. 😬

[@joshldyer]

with the drone? pretty sure you thought the camera moving around was a car lol

[@brettalan11]

The camera view is not simulating a vehicle. It's just showing how the traffic flows. You would have a red light in that spot where they're are crossing through.

[@nguyenchester]

Although this is good for interchange flow, how will this solve the backups on SR18? Getting onto I-90 EB is a nightmare because it’s only one lane.

[@Themrine2013]

It says in the video 18 is getting turned into a 4 lane road

[@rcassassin8592]

This is the exact concern I have as well. The i90 to sr18 traffic will block that intersection for those heading southbound on the parkway tryign to get to EB i90. Today we are lucky to get 3 cars through the intersection on a green light because of the traffic signal timings and volume of i90 offramp traffic. Looking at the new layout it doesn't address this problem and potentially makes it worse given the short distance between the two merge points. I'm still utterly baffled at why I90 to sr18 doesn't have a direct overpass to bypass that intersection alltogether given the massive volumes that occur in truck and vehicle traffic.

[@anniecruz186]

I have a concern that the westbound trucks entering the DDI to head west on highway 18 will tip over onto the traffic going the other way. What will keep them from going too fast to make that left turn? Now, when they go too fast to make the left turn onto highway 18 westbound, they land on the side of the road and the only risk is to the driver and their cargo (notwithstanding the traffic backup).

[@anniecruz186]

@wsdot I think that left turn is still too sharp. Can a bigger barrier be added to protect the cars going the other way?

[@wsdot]

The DDI ramps are designed with a wider turning radius, so it should allow for freight to transition more smoothly, reducing the likelihood of tipping. The transition will give vehicles more time to slow down before approaching the intersection and the additional WB SR 18 ramp with separate EB ramp will help traffic flow more smoothly.

[@EmeraldCityGuy]

I have become so sensitive to government entities touting statistics and percentages. If there are only 100 of these interchange designs in the USA, how can anyone know the long term affects like 50% reduction in accidents and the severity of them? Can you advise the cost differential of a design that utilized the fly-over merge versus this design? That type of merging would have eliminated areas of conflict except at the merge point.

[@wsdot]

The flyover design took up a much larger footprint which infringed on wildlife habitat and wetlands. It was also at least twice as expensive as the DDI design and didn’t offer significant enough improvements over the DDI that warranted the much higher price tag. Several stakeholder groups and community leaders were involved in selecting the DDI as the best choice for the location. The 50% reduction in collisions is mainly due to the removal of left-hand turn signals. This removes the possibility of being rear-ended or hit by oncoming traffic while making the left-hand turn. The DDI design keeps traffic flowing which will also improves safety during peak travel times.

[@connertheemmakaoricadencea1365]

Add a single point urben interchange

[@jefffinkbonner9551]

They take up too much room. The I-90 over passes would need to be rebuilt much longer--too expensive. Single point urban interchanges (SPUIs) would work well here traffic flow-wise, but the diverging diamond interchange (DDI) can fit under I-90 in the existing footprint.

[@craigwesson7913]

This solution will do nothing to reduce the backup that west bound 90 suffers at the interchange with the lights still at the exit ramp the semi's and cars will still back up especially when slow starting semi's get the green light the time it takes a semi to start moving through the intersection to the next light will in fact add to it and a lot more cars are going to run the yellow and red lights because the lights will be longer than they are now. What you need is an interchange like the one at the south end of 18 at interstate 5 and like I405 and 167. That way the heavier traffic coming from Snoqualmie will still get the free right to go to west I90 and the traffic from east I90 will get better flow. So yes the diverging diamond is good but using a overpass on to 18 from i90 is better

[@brettalan11]

I'm all for DDI in the places that it needs it, but to implement this design at 18/90 is truly asinine. Even if we have 2 lanes on both sides, you're going to STILL be forcing us to sit at traffic lights before we can enter 90. This passage is notorious for truckers, and their slow speeds already slow the rest of us down. Then to add insult to injury, ramp meters to go westbound on 90? There are going to be vehicles backed up at the ramps and then you got green lights for more vehicles to come in, and at some point we're all just going to get stuck. 18 to WB90 should be a continuous flow with no stops. When this thing gets built, I'll give it a solid year before we're all griping about how terrible this interchange is. I'd love to be optimistic about this project, but I am not convinced. The interchange in Lacey does not have the same volume of traffic as this intersection yet people keep comparing that interchange to this one and it is nowhere near the same. Make it make sense!

[@EVAUnit4A]

2:24 _"The carefully-designed approach angle of the intersections, along with clearly laid-out striping, arrows and signage will safely guide motorists through the new interchange."_ 2:24 The carefully-choreographed computer driver (POV) completely disregards a solid white line while approaching the controlled intersection and changes lanes less-than 100ft before the light, then ignores a non-powered signal light and continues without slowing or checking into the intersection, causing a _minimum_ three-vehicle collision. The POV driver- now a hit-and-run suspect, who appears to be driving an absolute *TANK* because the collision didn't even slow them down- continues on, and seconds later changes lanes with no turn signal or checking their blind spot. 2:42 _"Dashed lane lines guide you through the intersection. It's just that easy!"_ 2:42 The *TANK* changes lanes again without signaling or checking their blind spot. Second later, the POV Driver- for the second time in less-than fifteen seconds- crosses into an active intersection without stopping due to an un-powered signal light, resulting in _another_ hit-and-run with the opposing traffic. Confident in their superior understanding of the rules of the road in Washington State, the POV proceedes to cross lanes mid-intersection, and then finally climb up onto the hard raised left shoulder. *YES, THIS IS TRUE HAPPINESS.*

[@jefffinkbonner9551]

LOLOL GTA VII: Diverging Diamond

[@EVAUnit4A]

@@jefffinkbonner9551 _Exactly._

[@chevelleguns92]

Finally.... now lets hope people can figure out how to use it without playing bumper cars and cutting off semis we all know they cant merge on a single lane getting onto i5 or i90🤣

[@sharonholten5007]

Looks confusing

[@deadstick8624]

SO?! You still need to stop just as many times as right now. How does that improve flow? You're just making it look different. If anything, it looks more complicated than a lot of drivers can handle, especially ones who have a problem with navigating highways now. If you could design it to have less stops that would improve flow.That criss-cross pattern is the same as a four-way stop, it's just at a different angle.

[@marthaquigg7917]

The criss cross pattern is more like a 2 way stop because there are only 2 sides with cars approaching. It could be fun to give the one in Lacey a try, I like it!

[@deadstick8624]

@@marthaquigg7917 Hi Martha. How are you doing after the UW? Tony and his brother moved to Philadelphia. Tony is now a Professional Civil Engineer. He had been an engineer in training for four years, here, but is now in Philly as a Pro. By the way, I was the one who made the STEEL BRIDGE Logo several years ago. Thanks for commenting, and I may go and try the one in Lacey. I'm glad that YOU, a Civil Engineer that I know, made that comment so I could trust your thoughts on it and understand the NEW road pattern better. The video confuses me a bit because there doesn't seem to be a way to access I-5 south bound, coming the opposite way that the video is going (I believe the video is going West). I have one or two other questions, but that doesn't matter. The main one is what I mentioned in my first comment. But I trust you when you say that you like it, so it must be good.

[@reynochavier6297]

If you need practice driving through this type of intersection, try the one in Lacey. It's identical in its format.

[@brettalan11]

@@marthaquigg7917 People need to stop comparing this DDI to Lacey, because the road in Lacey is NOT a state highway. We're dealing with a different can of worms with this one, and this design is not the right solution for this interchange.