From SDOT:

Tomorrow, Friday, December 4, from 10 a.m. to 2 p.m. Seattle Department of Transportation crews will close the left lane of Alaskan Way Viaduct northbound at Massachusetts Street. During the closure, the crew will install a temporary railing until a permanent repair can be made. The guard rail was damaged by a recent one-car accident. Motorists should expect slowing and use caution through the work zone.