Lots of safety measures included.
It is a snowy day in Seattle this 4th of February. Snow or no snow, they opened the tunnel early this morning. See the two links below. The viaduct had the same design as the one that collapsed in San Francisco in 1989. It took the Nisqually earthquake here in the region to motivate decision-makers to replace it. Eighteen years later ...
This replaces the viaduct that will be coming down over the next six months:
This simulation of the seawall and the viaduct collapsing was used to help sell the need to spend $2B for the new tunnel.