Caltrans is planning to close all lanes of Highway 101 at Old Redwood Highway in Petaluma Saturday night.

The highway will be closed from 11 p.m. until 7 a.m. Sunday. The closure is needed to demolish the old overpass bridge. The $41 million Caltrans project to replace the Old Redwood Highway overpass and improve the interchange is scheduled for completion next year.

During the closure, northbound traffic will detour by exiting at Old Redwood Highway and turning right, continuing to Highway 116 in Cotati and returning to northbound Highway 101.

The southbound detour will involve exiting at Petaluma Boulevard North, turning right and continuing to East Washington Street and turning left and continuing to southbound Highway 101.

Prior to the full closure hours, there will be one-lane freeway closures in the northbound and southbound directions from 8 p.m. to 11 p.m. Saturday night.

After the full closure hours, there will be one-lane freeway closures in the northbound and southbound directions from 7 a.m. to 9 a.m. Sunday morning.

If this work is delayed due to weather conditions, it will be rescheduled for a later time, Caltrans said.