Changing the look of I-5 in downtown Seattle

Tony Black

Over a 48-hour period, the look of Interstate5 in downtown Seattle changed for the first time in almost 50 years.

A new flyover ramp, connecting State Route 520 directly to the I-5 express lanes, is taking shape. Crews set the foundation for that ramp – steel girders – over the May 19-21 weekend.

A before-and-after look at the steel girders placed over northbound I-5
and the express lanes in Seattle

The process itself is far from simple, and normally could take at least two full weekend closures of northbound I-5 to do. But with a busy construction season ahead, we wanted to minimize the disruption the best we could.

Together – the work and messaging – was a great example of teamwork between the public, our contractor Walsh and us. For that we thank you.

This wasn’t a “traditional” weekend closure as we worked with our contractor to stagger the closure times, leading to lots of questions. A Twitter thread
helped answer those questions.

What happened

Over the May 19-21 weekend, our contractor set and assembled 15 very large steel girders. The girders are 75-100 feet long, 5-feet-5 inches tall and weigh about 36,000 pounds.

They used two cranes to lift them and set them on the concrete piers and crossbeams you’ve seen sitting between northbound I-5 and the express lanes for a few months now.

The steel girders arrived by truckload in the days leading up to and during the closure.

This was no easy task, and at one point a lightning storm stopped all work. Crews needed to not only set the girders but bolt them down so we could safely reopen the lanes below for traffic.

In all, it involved two crews of 25 construction workers from Walsh, working alongside our inspectors and traffic operations over four shifts to pull this off. The result was a new bridge in one weekend, and northbound I-5 was closed for only 15 hours late Friday night into Saturday afternoon.

As the cranes position the girders, crews prepared to tighten them into the concrete piers.

Why steel?

We used steel girders because it would enhance the support of the type of traffic that will use this ramp, primarily transit and HOV carpools. The combination of curve of the road and length of the spans also made using steel the best option.

Two cranes lifted the pre-assembled steel girders into position.

What’s next?

Setting the girders is a significant milestone for our project and we are now entering what I call the “sweet spot” of this project.

In addition to building the new flyover ramp this year:

The westbound SR 520 off-ramp to East Roanoke Street is fully closed until 9 p.m. on June 17. This is so we can finish building a new retaining wall and then ultimately shift the Roanoke and northbound I-5 ramps to the north.

We have some more work to do on Mercer Street too and you can expect some lane and possible weekend closures there as well.

This project is still on track for a spring 2024 completion.

The final girders were set late Sunday night as crews finished the work in just 48 hours.

A final thank you

Just once more I want to thank everyone – you, the public, our contractor Walsh, and their partners for making this happen.

Spring/summer is always a busy time of year for construction, and we really need everyone’s help to keep things smooth and moving.