Work starts on final phase of 20-year $750 million Highway 101 project in Sonoma-Marin counties

The 20-year Marin-Sonoma Narrows Project will end up costing at least $754 million when it is finished in 2022.|

Blink and you might miss the recent lane shift on northbound Highway 101, just west of the dog park at Deer Creek Village in north Petaluma.

In mid-January, Caltrans redirected northbound traffic onto a pair of lanes in the median, just as the highway begins a gentle incline and crosses over the SMART railroad tracks.

Most drivers probably don’t even notice that subtle shift, which allows workers from Ghilotti Construction in Santa Rosa to keep widening that section of freeway from two to three lanes. To those tracking the progress of the Marin-Sonoma Narrows Project, that lane shift was a very big deal. It marked the beginning of a final part of this 20-year undertaking which, at long last, is on the homestretch.

The narrows project, which will end up costing at least $754 million, was designed as a kind of angioplasty for a chronically clogged traffic artery — a 16-mile 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 3.3-mile stretch of Petaluma, scheduled to be completed by mid- to late 2022, is Sonoma County’s final unfinished section of the narrows project.

“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.”

“It’s frankly very exciting that we’ve finally gotten to this stage,” said Jake Mackenzie, the former six-term Rohnert Park city councilmember and outgoing chair of the Metropolitan Transportation Commission. “We’re talking more than 20 years of political battles, enviros versus the developers, as to whether the highway should be widened or not.”

Since 2001, work on the narrows project has proceeded in stages as money became available. The $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 defrayed by $85 million from a state gas tax increase, $28 million from Sonoma County’s Measure M sales tax.

The city of Petaluma kicked in an additional $7 million to elongate an elevated section of highway that goes over the site of the proposed Rainier crosstown connector project. Although the project is still in the design phase, the plan is to eventually extend Rainier Avenue from McDowell Boulevard west to Petaluma Boulevard North, providing Petalumans another option for getting across town.

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. On the night of Friday, Feb. 6, Caltrans will commence tearing down those vacated northbound lanes, then replace them with new ones, said Jeff Weiss, a spokesman for the agency.

That elevated section of the freeway, called the Petaluma Overhead, passes over the SMART tracks and multiuse path. Northbound work is expected to be finished by the end of 2021, with this phase of the project completed sometime in 2022.

Mackenzie, 81, recalls commuting to San Francisco in the early 1970s. Back then, he said, Highway 101 went right through downtown Novato. “There was no bypass yet,” he said.

For a half century, he marveled, between his professional and political lives, “I’ve been involved with the 101 corridor. I’m delighted we’re finally getting the Sonoma County part complete.”

Once the Petaluma part is wrapped up, the sole remaining unfinished part of the narrows project will be a 6-mile Marin County segment, from Atherton Avenue in Novato to San Antonio Road, just south of the Marin-Sonoma County line.

That widening work, to be paid for with $40 million in gas tax revenues, begins this spring and should be finished in late 2023 or early 2024 — a quarter century after a consulting team headed by urban planner Peter Calthorpe submitted its final recommendations to Marin and Sonoma County officials.

That 196-page report called for “multi-modal” transportation solutions: improvements to both the highway and arterial roads; to bus and ferry service, bicycle and pedestrian accessibility, and the construction of rail service along the Highway 101 corridor.

With SMART operating, with the freeway widened, and at least some of the promised bike lanes completed, “we’re finally realizing the vision Peter Calthorpe had in 1997,” Mackenzie said.

“We are getting there,” agreed Sonoma County Supervisor David Rabbitt, a longtime SMART director who was chosen earlier this month to lead the passenger rail line’s board. Once this final Petaluma segment of the narrows project is complete, he added, “our job in Sonoma County is going to be done.”

What’s true of all infrastructure and public works projects, Rabbitt said, is that “they usually take longer than you think, and cost more than they should.

“But these are generational investments, and pretty important things to continue. So we just have to keep slogging away,” he said.

You can reach Staff Writer Austin Murphy at 707-521-5214 or or on Twitter @ausmurph88.

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