This temporary closure is all about monitoring the viaduct and giving the public time to plan ahead. Closing the viaduct will give crews better access to the structure for monitoring while Bertha tunnels beneath it.
We have ways to monitor ground movement on surface streets without closing them, but the best way to keep a close eye on the viaduct is to remove traffic.
It’s safe for drivers and pedestrians to be under and near the viaduct during tunneling. If it weren’t safe, we would restrict access.
STP’s structural engineers don’t expect the tunneling operation to significantly affect the viaduct or the ground beneath it.
That being said, we will be monitoring conditions around the clock and have planned for many contingencies – WSDOT, SDOT and Washington State Ferries have plans in place if we need to close a portion of the surface street.