Here’s an early warning: Caltrans plans to close Commerce Boulevard under Highway 101 in Rohnert Park for 12 days starting about Aug. 1.

Caltrans spokesman Robert Haus said that during the closure construction crews will tear down 101’s current north and southbound overpass in order to begin building a new southbound overpass.

Northbound 101 traffic is due to be switched over to the new Wilfred Avenue/Commerce overpass on July 22 with southbound traffic being shifted over July 29. Around the 29th, Haus said, the Santa Rosa Avenue onramp is to be opened for southbound traffic along with the new southbound Wilfred Avenue offramp.

Further south, Haus said, work is starting on widening 101 in Novato, from Highway 37 to about Atherton Avenue, with a groundbreaking ceremony set for Thursday.