Southbound Highway 101 to close overnight Saturday in Marin County for reroute of gas line around mudslide

State transportation authorities announced Saturday a plan to close all lanes of southbound Highway 101 in Marin County overnight Saturday into Sunday morning to reroute a gas line affected by a slide that has buckled a stretch of frontage road north of Novato.

Traffic Advisory for full closure of US-101 southbound in Marin County 3-25-2023.pdf

The slide, unleashed in Tuesday’s heavy rains, has impacted a 100-foot segment of Redwood Boulevard that runs between Olompali State Historic Park and Highway 101.

The hillside has encroached onto the road’s west side, lifting and buckling large pieces of the asphalt surface.

The closure is set to extend from 9 p.m. Saturday to 9 a.m. Sunday.

The recommended detour for southbound drivers makes use of Highway 116 to Lakeville Highway and westbound Highway 37, which connects to Highway 101 south of the closure.

“Luckily this is not during a workweek, and it is at night so the traffic impact won’t be as big,” said Caltrans spokesperson Matt O’Donnell.

Still, in situations like these, “we ask people to slow down,” O’Donnell said, given that traffic is likely to be higher than usual on Highway 116 and Highway 37, a busy state route.

Caltrans is assisting Marin County and PG&E with the road closure. The agency had been monitoring all week and got word Friday the freeway would need to close temporarily.

PG&E has two underground gas transmission lines in the area. One was exposed at the top of the mudslide and the second was buried beneath the slide.

PG&E earlier this week had reduced operating pressure on that buried line.

Ahead of another expected storm this coming week, PG&E plans to build a temporary pipeline bypass that avoids the affected slope.

“Service to PG&E gas customers will not be impacted during the construction of the bypass or when it is in service,” PG&E spokesperson Karly Hernandez said in a statement Saturday. “At this time, we have identified no risk to the public and do not anticipate a disruption to gas service for customers served by these.”

The slide was also reported to be affecting a water aqueduct that carries supplies from Sonoma to Marin County for the North Marin Water District.

Redwood Boulevard is the only access road into Olompali State Historic Park and it is closed indefinitely to vehicles and cyclists, all but shuttering the park.

For traffic updates, follow @511SFBay. For live traffic conditions, go to quickmap.dot.ca.gov.

Staff Writer Marisa Endicott contributed to this story.