Northbound Highway 101 in Petaluma gets third lane early Thursday

Early Thursday morning workers are set to complete widening the northbound side of the Washington Creek bridge between Lakeville Highway and the Lynch Creek Trail bridge, according to a Caltrans press release sent on Tuesday.

The newly widened Washington Creek bridge will be the last piece needed to complete an uninterrupted three-lane freeway going northbound between Marin County and Windsor, a 30-mile stretch.

But officials said the carpool lane will not stay in its current location once the southbound portion is widened. Caltrans plans to open the southbound carpool lane in late 2022, at which time the northbound lane will move over to its permanent location.

The Petaluma Widening Project is one of 13 projects of the larger Marin/Sonoma Narrows widening project to add a carpool lane in each direction of U.S. Highway 101 between Route 37 in Marin County and Corona Road in northern Petaluma.

The final project will begin in spring 2022, which will add carpool lanes between Novato and the Marin/Sonoma county border.

The Marin-Sonoma Narrows Project has been ongoing for 20 years and the current work is part of its final phase. The entire project is expected to cost at least $754 million, and the existing phase should wrap up by late 2022.

That widening work begins this spring and should be finished in late 2023 or early 2024.

For more information and live traffic updates, residents can go to 511.org.

Press Democrat reporter Colin Atagi contributed to this report.

Amelia Parreira is a staff writer for the Argus-Courier. She can be reached at amelia.parreira@arguscourier.com or 707-521-5208.