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SR 99 tunnel’s north portal taking shape near the Space Needle

A few blocks northeast of the Space Needle, crews are building the north portal of the SR 99 tunnel. It’s a huge piece of the overall tunnel project, but it’s largely invisible to the thousands of people that pass by it every day.

About the only place you can see the north portal taking shape is from the viewing deck of the Space Needle because most of the construction is underground, inside a pit that’s every bit as impressive as the launch pit where Bertha, the SR 99 tunneling machine, started her journey under Downtown Seattle.

The receiving pit is where Bertha will break through at the end of her tunneling trek – it’s at the south end of the north portal site. But as you can see from this photo, there’s a lot more going on. The north end of the pit is where drivers will enter and leave the tunnel. From there it’s another 500 feet to the wall that Bertha will break through.

In that 500-foot-long stretch, crews are building another tunnel. It’s called a cut-and-cover tunnel because it’s basically a big trench with a lid on top (the Battery Street Tunnel and the I-5 tunnel under the Convention Center and Freeway Park are also cut-and-cover tunnels). On the SR 99 Tunnel Project, cut-and-cover tunnels at the north and south portals will serve as connectors linking the bored tunnel to the surface.

As you may have noticed, there’s no lid yet, but everything you see will eventually be covered. It may be hard to imagine, but this visualization should help you look into the future.

Ongoing north portal updates are available here, and don't forget you can watch north portal construction progress on our construction cameras.