East Blithedale's traffic problem is bigger than its signals

On Tuesday, December 9, traffic engineers took four drives along East Blithedale Avenue heading toward Highway 101 during the afternoon commute. They had activated Mill Valley's new adaptive signal system the month before and wanted to see if it had made a difference. Their average speed on those four drives? 5.9 miles per hour, according to the evaluation.

A person walks at around 3 mph. A cyclist moves twice as fast as those cars that day. But the afternoon backup on Blithedale was never a problem that smarter signals were going to fix.

What's working: The city activated the system last November on East Blithedale from Camino Alto to Lomita Drive, and on Camino Alto from Miller Avenue to Sycamore Avenue, according to a February 2026 evaluation by Kimley-Horn, the engineering firm the city retained to deploy and assess it. The software adjusts signal timing in real time based on actual traffic demand. The City Council received the first performance evaluation Monday night.

The evaluation compared crowd-sourced travel time data averaged across many weeks before and after activation. Midday travel times dropped 13.6 percent eastbound and 11.6 percent westbound. Weekend times fell roughly 8 percent in both directions. The system is doing what it was built to do for drivers on Blithedale between 11am and 3pm, or on a Saturday.

What isn't working: Afternoon peak times heading east, the drive toward Highway 101 between 3 and 6pm, rose 4.3 percent over the same comparison period. The broader travel time data is consistent with afternoon eastbound being the worst period on the corridor, and the adaptive system did not change that. The reasons why go beyond signal timing.

The context: According to the signal timing review presented Monday, the two signals closest to the Highway 101 interchange off-ramps, are controlled by Caltrans, not the city. According to a Transportation Authority of Marin (TAM) interchange study, the area around those signals experiences congestion during morning, after-school, and evening peak periods, with eastbound backups extending into Mill Valley.

Last June, Caltrans also activated ramp metering on the northbound 101 on-ramp at Tiburon Boulevard as part of a broader initiative in Marin County. Caltrans told the Briefing its own monitoring data shows the metering improved freeway travel times and that video observation showed no noticeable spillback onto local streets.

No independent assessment of the metering's impact on local streets has been published. Caltrans acknowledged that during heavy congestion, spillback "may not be avoidable, with or without ramp metering operations.” Council members called on staff to keep pushing Caltrans on signal coordination at the interchange.

What the data says: The city's Traffic Report Card measures travel times on a 1.5-mile stretch of E Blithedale from Millwood Street to Highway 101. Those times have ranged from an average of 9 minutes in 12/13 to over 14 mins in 15/16 to 10:20 mins in 23/24.

Councilmember Urban Carmel told the Briefing: "There is no clear trend in travel times. 2015/16 was the worst year for traffic and 2023/24 was one of the best. Years in between have varied from high to low." A Briefing review of the full dataset found no clear direction. This year, at around 11:20 mins, was close to the thirteen-year median.

What's next: The longer-term relief, if it comes, will require changing the highway itself. TAM has identified the East Blithedale and Tiburon Boulevard interchange bridge as a priority for redesign and potential widening. According to TAM's published project schedule, design of a preferred alternative begins around 2029/30. Councilmember Carmel, the city's TAM liaison, said he believes construction could begin within five years if all goes well. Planning is funded through Measure AA, the half-cent Marin transportation sales tax approved by voters in 2018. Construction funding has not been secured, according to TAM's project documentation.

A separate project, documented on TAM's project pages, would add a direct connector between northbound 101 and eastbound 580, reducing regional through-traffic on the stretch of highway that runs past Mill Valley. That project is in earlier planning stages.

The bigger picture: Both projects are years away. And even if they succeed, adding capacity tends to attract more drivers until congestion returns to its previous level, a principle traffic engineers call induced demand. Councilmember Stephen Burke made that point at Monday's meeting. "We are the problem," Burke said. "Our behavior is the problem.”

But Burke also called for more engagement and invited the city's staff to present to the Transportation Commission, known as TMAC, for what he described as a deeper dive with residents and professionals in the transportation field. "I think we could really learn a lot," Burke said, "and then be able to educate our residents better as to what we're trying to do, where our failure points are, where opportunities are."

In the near future: Caltrans is already moving on one piece of that. The agency confirmed to the Briefing that the creation of bike lanes across the Highway 101 overpass, connecting Mill Valley and Strawberry, begins in late summer of this year.

One hundred years ago this Friday, the students of Old Mill School marked Mother's Day with a formal assembly that filled the stage with greens and white flowers.

The school had only been open five years. It opened November 19, 1921, at a total construction cost of $85,000.

Mrs. R. E. Ewing sat in a place of honor as the program's special guest, representing what the school called "the mother idea." Students led the flag salute, recited the American's Creed, and delivered speeches on the value of mothers. Four boys, George Neale, Joseph Costa, Irvin Grossman and James Chesnut, sang "Mother Machree." At the close, a boy and a girl each presented Mrs. Ewing with a bouquet. There was a large attendance of mothers.

Mother's Day had only been a national observance since 1914 and Mill Valley's kids were early enthusiasts.

Old Mill School is still there on Throckmorton Avenue, 100 years later.

Source: Mill Valley Record, May 8, 1926.

🚶 Federal money is coming to fix six pedestrian crossings in Mill Valley. We reported on which intersections made the list, why, and what it will actually cost the city after Washington picks up its share.

🏗️ Mill Valley permitted $14.3 million in construction work in April, the highest single month of the year. We pulled the numbers, put them in context against neighboring cities, and tracked down the downtown housing project that finally cleared after two years in approvals.

🛣️ The city adopted a five-year paving plan. We built a searchable tool so you can type in your street and see when work is coming and what kind. We also reported on the ballot measure that has to pass in November for years three through five to hold.

🚌 Two separate reports landed the same week: one from Marin Transit on the Muir Woods Shuttle, one from the city on Shoreline Highway traffic. We read both and reported on what they looked like next to each other.

📵 The Tam Union board voted 3-2 to spend $113,000 on phone pouches for every student. We covered the vote, the dissent, and what a student speaker told the board before the decision that didn't change the outcome.

Mon, May 11 – Window on the Work: Pictures from Home, Mill Valley Library Creekside Room, 6:30pm to 8pm. An in-depth discussion on Sharr White’s play, exploring the design and rehearsal process behind the production. Registration required.

Tue, May 12 – Tam High Rock Bands, Sweetwater, 7pm. Shred the night away with the hardest rockers in the 94941 as local students take the legendary stage. Doors open at 6:00pm.

Tue, May 12 – Tuesday Night Comedy, Throckmorton Theatre, 8pm to 10pm. The long-running weekly stand-up showcase featuring a rotating lineup of veteran and rising comics.

Wed, May 13 – Author Talk: Portia Elan with Michael David Lukas, Mill Valley Library Creekside Room, 6:30pm. An evening discussion featuring the local author in conversation with the National Book Award finalist.

Wed, May 13 – Caroline de Lone, Joe Endoso & Friends, Sweetwater, 8pm. A live performance featuring local talent at the historic 19 Corte Madera Ave venue. All ages; doors open at 7:00pm.

Thu, May 14 – Bread & Roses Spring Benefit Concert, Sweetwater Music Hall, 7pm. Featuring performances by Ron Artis II and Rainbow Girls to support the nonprofit's mission of bringing live music to institutionalized audiences.

Fri, May 15 – Outdoor Movie Night: Zootopia 2, Strawberry Majors Baseball Field, 5:30pm to 10pm. A free community event in Strawberry Point featuring jump houses, food vendors and a sunset screening. Bring blankets and chairs; movie starts around 8:00pm. No dogs allowed; pre-registration required.

Fri, May 15 – Musical: Into the Woods, Throckmorton Theatre, 7pm to 9:30pm (Sat, 12; Sun, 2). Opening night for this spellbinding Stephen Sondheim musical journey where fairy tale wishes come true - at a price.

Fri, May 15 – Sabbath Lives – A Tribute to Ozzy Osbourne & Black Sabbath, Sweetwater Music Hall, 8pm. A high-energy tribute performance covering the catalog of the heavy metal legends. All ages; doors open at 7:00pm.

Sat, May 16 – The Great Train Heist, Mill Valley Library Creekside Room, 1pm. A community discussion exploring the history and impact of the Sonoma-Marin Area Rail Transit (SMART).

Sun, May 17 – School of Rock, Sweetwater Music Hall, 10:30am. A morning showcase featuring talented student musicians performing rock classics. All ages; doors open at 10:00am.

Sun, May 17 – Josh Zee and Friends Sunday Residency, Sweetwater Music Hall, 6pm. A free weekly residency performance at the venue. No tickets required; all ages welcome; doors open at 5:00pm.

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