Highway 101 will be closed in Petaluma at times this week for the installation of "falsework," a temporary structure to support the components of a bridge during construction.

All northbound lanes at the Petaluma Boulevard South interchange will be closed tonight and Thursday nights, beginning at midnight and ending at 6 a.m.

One southbound lane will also be closed during the work.

Construction signs will direct motorists to a detour.

During the closure, Caltrans will temporarily reopen the former Petaluma Boulevard South off-ramp. Motorists will exit at Petaluma Boulevard South, continue to the northbound Petaluma Boulevard South on-ramp and return to the freeway.

The Southbound Petaluma Boulevard South on-ramp and off-ramp will remain open during the northbound closure.

On Friday, southbound 101 will be closed from 11 p.m. to 6 a.m.

The detour will route drivers to exit at Highway 116 to Lakeville Highway, on to Highway 37, then back to 101.

The on- and off-ramps for southbound 101 at Petaluma Boulevard South will be closed. The northbound on-ramp and off-ramps will remain open.