The International Information Center for Structural Engineers

It was April 4, 2017, when the work of tunneling machine Bertha was complete, breaking through into her disassembly pit and marking the end of the 1.75-mile long State Route 99 (SR 99) tunnel beneath Seattle. Now, the Washington State Department of Transportation released a drone video that shows the ongoing construction work from end-to-end inside the tunnel.

The tunnel will become a double-decker highway, scheduled to open in 2019