Construction on Highway 101 will cause road and ramp closures in Petaluma starting this week, Caltrans said.

Lakeville Highway will be closed under Highway 101 at night from 10 p.m. to 5 a.m., tonight through Thursday. A detour is available on Caulfield Lane.

Petaluma Boulevard South under Highway 101 will be closed for 20 hours on Feb. 8 as crews demolish the old Petaluma River Bridge. The road and the northbound Highway 101 offramp at that spot will be closed from 4 a.m. to midnight. Detours will be posted in various locations. The work has been rescheduled from Feb. 1.

Caltrans also said that a new northbound onramp at Petaluma Boulevard South would open in three to four weeks, but the agency did not give an exact date. The onramp has been closed since last fall, when highway traffic was shifted onto a raised median south of Petaluma.

The closures depend on weather conditions and will be rescheduled if necessary, Caltrans said.