Another Reminder of the Futility of Carpool Lanes

Contributor's note: This is an update to the October 24, 2025, blog post, "When Carpool Lanes Cause Mayhem."

Rachel Swan, the San Francisco Chronicle's transportation reporter, framed the change in carpool hours on Highway 101 in Marin and Sonoma counties in the San Francisco Bay Area as a win for solo drivers.  

Following a torrent of complaints, Caltrans has reduced the hours for a 52-mile carpool lane on Highway 101 through Marin and Sonoma counties. As of Monday [March 2], new signs along the freeway show the lane will be reserved for high-occupancy vehicles heading south between 6 and 9 a.m., and for those heading north from 3 to 6:30 p.m. 

That’s a two-hour reduction for the morning rush hour, given that Caltrans had set the carpool period from 5 to 10 a.m. when officials opened the lanes in October. During the evenings, agency staff shrank the carpool schedule by half an hour. It had previously ended at 7 p.m.

The 16-mile stretch of new carpool, aka high occupancy vehicle or HOV lanes, known as the Marin-Sonoma Narrows Project, opened on Sept. 29, 2025 "after nearly 30 years of work," according to the 4-page Caltrans 'Marin-Sonoma US 101 Corridor Briefer' [pdf] on the project.

[In his piece in The Press Democrat published on opening day, Austin Murphy describes the time-frame differently based on segments of the corridor. His reporting was the basis for the aforementioned blog post].

The opening of those lanes, and closing of those chokepoints, marks the completion of the Marin-Sonoma Narrows project, which focused on a 16-mile stretch of the highway between Novato [Marin Co.] and Petaluma [Sonoma Co.]. Work on that project began in 2011 and has cost an estimated $762 million.

That undertaking was part of an even larger, roughly $1.5 billion public works project designed to create a continuous carpool lane from Sausalito to Windsor – a vision which, as of Monday, has now been realized.

The 52-miles of continuous carpool lanes is the second longest in the Golden State after the 70-mile northbound HOV lane on Interstate 405 in Los Angeles, "the longest in the nation," as of May 23, 2014.

Swan attributes the change of carpool hours to angry motorists airing their frustration with the Bay Area's regional transportation planning agency.

Scores of people called or emailed the Metropolitan Transportation Commission throughout the fall to express their misgivings about the new carpool lane hours, according to commission spokesperson John Goodwin. The criticism tapered off after Caltrans reneged, and now that the new signs are up, North Bay residents seem mollified.