Video: I-90/SR 18 improvement project update, Diverging Diamond Interchange savings helps widen SR 18

On Friday, May 19, 2017, the City of Snoqualmie released a YouTube video detailing improvement plans for the congested and dangerous I-90/SR 18 interchange. The design and planning stage of the improvement project should begin in July 2017.

The $150 million state transportation project originally wasn’t slated to be funded until 2023, but 5th District representatives were able to push the project up during the 2017 legislative session.

Snoqualmie Mayor Matt Larson explains the history of the 90/18 interchange improvement project, along with construction timeline in the recently released video.

WSDOT plans to use an uncommon traffic solution at the busy interchange called a Diverging Diamond Interchange (DDI), instead of an expensive flyover ramp. The realized savings will then be used to widen the SR 18 corridor between I-90 and Tiger Mountain in order to keep traffic from backing up on I-90, which currently occurs during peak commute hours.

You can find out more about what’s in store for the 90/18 interchange, including how DDI’s work, below: 

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  • Oh no, not this again. Here is a link to what this is since the article didn’t have it.
    What this does is transfer traffic from the right side of the road to the *left* side of the road through the interchange area, and then back again afterwards. I can’t imagine of how much this is going to cause problems in our area – where literally no one has even seen one of these, let alone has driven on one. And then the tourists. And heavy rain/poor visibility conditions. And snow. The number of head on collisions that could happen frequently is mind boggling.
    We can do much better than this. Don’t put the fastest/cheapest thing in place – especially if that thing is incredibly stupid. Let’s actually build a solution that makes sense and will handle the traffic loads expected through at least 2030.
    I’m not surprised Mayor Larson is supporting this. I’ll vote for anyone else to get different leadership in charge of Snoqualmie.

    1. It’s really not complicated at all Not sure it will have much of an impact since the majority of traffic is all caused by the bottlenecks in 18. But surprise! By choosing this lane restriping to better facilitate traffic flow the state now has the money to make 18 4-lanes and eliminate the bottle neck. Though the road has curves so slow traffic will probably always be a problem.

  • Totally agree, just look at the basic traffic circle. People are confused sometimes. They will not figure out a diverging diamond…. no way. There will be cars stopped at the interchange trying to figure it out.

  • The video lists many locations where this has been done for years, apparently without much problem. We currently have accidents and incredible delays, lets support a fix now instead of something that won’t happen for a decade or more and even then doesn’t solve Snoqualmie’s access problems.

  • We relocated to Colorado from Snoqualmie 7 years ago, and one of these was put in nearby. People freaked out about it before it was completed. It did seem confusing when I looked at images, and heard a horror story from a friend at that off ramp from her brother who lives near one in Utah.. Once completed, I hardly hear a complaint. My brother was visiting from Iowa a few weeks ago and had to use his to drop off our son, and he said it wasn’t a big deal at all. I dreaded that interchange before (mostly because I was stuck at lights forever), and I really don’t anymore. That said, its used at and off/on ramps between two towns (Superior/Louisville) that are both fairly busy with large businesses (Costco, Target, Lowe’s, etc.) on the sides of the freeway, as well as lots of residences nearby. The implementation at I-90/Hwy 18 is different, but it seems to me it could be a really helpful solution. I moved into Snoqualmie in 2000, and over the years before the light was put in, became terrified of some of those turns, racing to beat the trucks, or waiting forever to make the turn. It really should help that!

  • If drivers have issues figuring out concepts like diverging diamonds and traffic circles, a much better solution than avoiding these concepts is to revoke their licenses as they are not skilled enough drivers to be on the road to begin with.

  • Living Snoqualmie