Construction begins on final phase of Sonoma-Marin Highway 101

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Construction has begun on the final phase of the Sonoma-Marin Highway 101, a project that has been in the works for 20 years and has cost nearly US$754 million. The narrows project was designed as a kind of angioplasty for a chronically clogged traffic artery, a 26 kilometer stretch of Highway 101, from state Route 37 in Marin County to Corona Road, just north of Petaluma Village Premium Outlets. The construction of carpool lanes through a 5.3 kilometer stretch of Petaluma, scheduled to be completed by mid-to-late 2022, is Sonoma County’s final unfinished section of the narrows project.

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Since 2001, work on the Sonoma-Marin Highway has progressed in stages as funds became available. The US$121 million price tag for this final Sonoma County stretch, adding carpool lanes in both directions between the Petaluma River and Corona Road, and replacing an elevated section of the freeway, was settled by US$85 million from a state gas tax increase, US$28 million from Sonoma County’s Measure M sales tax. For the time being, traffic on Highway 101 just north of the East Washington Avenue on-ramp has been diverted onto what was formerly the highway’s median. Once the Petaluma part is wrapped up, the last remaining incomplete part of the narrows project will be a 10 kilometer Marin County segment, from Atherton Avenue in Novato to San Antonio Road, just south of the Marin-Sonoma County line.

“It’s definitely the seventh-inning stretch,” said Suzanne Smith, executive director of Sonoma County Transportation Authority. “We’ve still got another year and a half of construction, but by the end of 2022, we should all be driving on those new lanes.” Jake Mackenzie, the former six-term Rohnert Park city councilmember and outgoing chair of the Metropolitan Transportation Commission said “it is frankly very exciting that we’ve finally gotten to this stage. We’re talking more than 20 years of political battles, enviros versus the developers, as to whether the highway should be widened or not.”