Tiburon bike lanes pushed to 2029 as Caltrans proceeds along rest of corridor

A phased map provided by Caltrans shows the intended rollout of bike lines along Highway 131, also known as East Blithedale Drive and Tiburon Boulevard. Phase 1 next summer would include new lanes east of Tiburon town limits to Mill Valley, while Phase 2 would include new lanes within Tiburon town limits. (via Caltrans)

Caltrans has confirmed it will pursue Tiburon Boulevard bike lanes within town limits in a second phase of improvements — with funding to be secured next year and construction targeted for early 2029 — as the final design is now complete for its 4.6-mile Mill Valley-to-Tiburon pavement project set to start next summer.

The Phase 1 start date hinges on Tiburon first completing a separate project to install underground conduit for fiber-optic cables along the boulevard, agency spokesperson Matt O’Donnell said. The town took on the work after Caltrans considered adding it to the maintenance project but ultimately deferred.

The Caltrans improvements along state-owned Highway 131, which doubles as East Blithedale Avenue in Mill Valley and as Tiburon Boulevard east of the southbound Highway 101 on-ramp, are expected to take a year, wrapping in summer 2027. They include repaving, drainage upgrades, guardrails, curb ramps, signs, traffic signals, lighting, crosswalks and intersection improvements. The California Transportation Commission in October allocated $18.57 million toward the work, though Matt O’Donnell said construction costs would be closer to $15.2 million.

Phase 2 would include a stakeholder task force “to provide inclusive community input and develop an endorsed scope and configuration for bikeway and transit improvements,” O’Donnell said.

Caltrans, the county and Southern Marin Supervisor Stephanie Moulton-Peters are coordinating to select a task-force facilitator, O’Donnell said, as the agency looks to “finalize task-force membership and convene the group in early 2026.”

New lanes coming to Mill Valley, unincorporated areas

Caltrans will, however, proceed with creating new Class 2 bike lanes on both sides of the road in Mill Valley, Strawberry and unincorporated Tiburon, starting from Mill Valley’s Tower Road-East Blithedale intersection. The lanes will run along the Highway 101 overpass, becoming Class 4 protected bikeways on Tiburon Boulevard at South Knoll Road and North Knoll Road before ending at Blackfield Drive.

On the south side, a temporary Class 1 multiuse path — with a permanent path to follow in Phase 2 — will be created between Strawberry and Blackfield drives. That path leads to the existing Class 3 bike route along Greenwood Cove Drive and Greenwood Beach Road, where residents have long complained about bike traffic and have sought to redirect faster cyclists out to Tiburon Boulevard.

Within town limits, however, Caltrans reversed course on including bike lanes between Blackfield Drive and Trestle Glen Boulevard after the Tiburon Peninsula Traffic Alliance, the Reed Union School District and the city of Belvedere raised concerns that the lanes would disrupt school-bus service.

Town conduit project must come first

Tiburon Public Works engineering manager David Eshoo said the town is targeting the broadband conduit installation for spring and summer 2026, with a goal of finishing by July, which is when Eshoo said Caltrans looked to start its project. The two-to-three-month project would require Town Council approval before getting underway.

Design and environmental review are 95% complete, Eshoo said, and the town expects an encroachment permit from Caltrans within weeks. Construction costs were estimated at $2 million when the town completed its strategic plan.

The fiber-optic conduit could eventually connect traffic signals along Tiburon Boulevard to networks that determine optimal signal timing, including through artificial intelligence, Eshoo confirmed.

San Anselmo in August installed AI-powered traffic signals at the Hub, widely considered Marin’s most congested intersection, at Sir Francis Drake Boulevard and Red Hill Avenue. Local interest in AI signals for Tiburon Boulevard has grown after an initial analysis found wait times dropped more than 30% at peak hours at the Hub, and San Anselmo is now expanding the technology to all 12 of its traffic lights with help from a $250,000 Transportation Authority of Marin grant.

School-bus concerns prompted reversal

Caltrans officials as early as July indicated the agency would defer the Tiburon Boulevard bike lanes between Blackfield Drive and Trestle Glen Boulevard after the Traffic Alliance, which operates the local school-bus program, asserted bus provider First Student would not serve four stops if the lanes were installed: outbound at Jefferson Drive and inbound at the 76 gas station, Cecilia Way and Blackie’s Pasture.

However, investigations have cast doubt on three of those four claimed impacts.

Bike-advocacy group WTB-TAM in September noted the bus stop at Blackie’s Pasture is located past where the inbound bike lanes would end, at the entrance to the parking lot — meaning that stop would not be affected.

The group also said it observed no students getting picked up at the inbound Cecilia Way stop on Aug. 29 and Sept. 5, as the bus skipped the stop both times. The Ark observed the same route skip the stop Sept. 12.

WTB-TAM representatives further noted the street width at the bus stop near the 76 gas station measures 22 feet between the curb and the vehicle lane, giving “more than ample space” for buses to enter, pick up students and exit without blocking traffic. A standard school bus is 8½ feet wide.

That left Jefferson Drive as the sole stop with a documented conflict. Bike advocates requested a compromise to delay implementation of only the northern bike lanes until design improvements could be made for Phase 2, but Caltrans instead deferred the entire segment.

The Traffic Alliance publicly made other false and misleading assertions during its campaign against the lanes. It claimed they were not part of Caltrans’ original proposal and were added only under pressure from bicycle advocates, though the lanes were included in the agency’s plans from inception. It also misinterpreted state vehicle codes to suggest buses cannot legally block a bike lane at a designated stop statewide, wrongly claimed public transit has priority over pedestrians and cyclists under Caltrans’ Complete Streets directive and incorrectly asserted Caltrans violated its own speed-limit-based guidelines in proposing Class 2 lanes on the boulevard.

The Traffic Alliance has also attributed safety and policy positions to bus provider First Student that the company has repeatedly declined to independently confirm. First Student’s practices in other jurisdictions do not align with the positions the Traffic Alliance has attributed to it.

Traffic Alliance Chair Bob McCaskill, a Belvedere resident and one of the leading voices against the bike lanes, did not respond to requests for comment.

In the meantime, WTB-TAM Planning Director Matthew Hartzell said his group looked forward to Phase 2, as it “will hopefully complete the protected bike lanes all the way to Trestle Glen Boulevard.”

He said the group also looked forward to addressing community concerns about bicycle-bus interactions at stops, along with left turns onto Tiburon Boulevard from Cecilia Way.

“Our focus remains on the accurate presentation of facts, and we look forward to clarifying several misunderstandings that have been introduced into the public discussion,” Hartzell said.

Tiburon Mayor Holli Thier, who had supported the bike lanes’ inclusion and pushed for Caltrans to incorporate fiber-optic conduit in its plan, said she was “pleased to see Caltrans has incorporated our community’s and stakeholders’ concerns.”

“We must now prioritize Phase 2, funding and working closely with Caltrans to ensure bike lanes, bus stops and other elements of the plan are done safely with community input,” she said.

However, she initially declined to comment on the town’s broadband plans. When The Ark told her that both O’Donnell of Caltrans and Eshoo of the town of Tiburon have said the town would take the lead on the project, she said she was “waiting to hear back from a few folks.”

“I am hopeful that Caltrans will work with Tiburon to find a way to do this project jointly so as to save money for the taxpayers in Tiburon and in the state of California,” she said. “I understand that part of Caltrans’ goals are to save the state money, and not working together will increase the cost for all.”

Reach Francisco Martinez at 415-944-4634.

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