On Friday night, Caltrans plans to switch northbound traffic to the Highway 101 median lanes being constructed south of the Petaluma River Bridge.

The northbound on-ramp from Petaluma Boulevard South will be closed while construction workers raise the old northbound lanes and construct an on-ramp to match the height of the new roadway. The ramp closure is expected to last at least eight weeks and possibly longer, depending on weather conditions during construction.

During the traffic shift on Friday night, the northbound off-ramp to Petaluma Boulevard South will be closed from 9 p.m. Friday night until 5 a.m. Saturday morning.

For a detour during the long-term northbound ramp closure, take Petaluma Boulevard South, turn right on D Street, then turn right on Lakeville Street and continue to northbound Highway 101.