The Caldecott Tunnel's three oldest bores will get a $267 million renovation tentatively starting in November. It is the biggest upgrade to the Lamorinda commuter route since the fourth bore opened in 2013.

The project will replace aging ventilation fans with jet fans for smoke control in a fire and repair cracked and water-damaged walls and ceilings. Crews will also install a sprinkler system in all three bores, upgrade drainage and add LED lighting, according to the California Department of Transportation's project page. Construction is tentatively set to wrap up in fall 2029.

More than 160,000 drivers pass through the tunnel on State Route 24 each day, according to the Contra Costa Transportation Authority. During the three-year construction window, at least two bores will stay open at all times, one in each direction, the East Bay Times reported. Some work will take place on evenings and weekends.

An independent consultant, WSP, found that Bores 1, 2 and 3 rank among the top risk priorities in California for ventilation upgrades, according to Caltrans.

"The Caldecott Tunnel has always been a very critical, vital transportation link between Contra Costa County and the rest of the Bay Area," former Orinda Mayor Amy Worth said. Worth, who chaired the Metropolitan Transportation Commission (MTC) and helped push the fourth bore to completion, called it "joyous news that this is in the budget and will be moving forward."

Worth said tunnel renovations require broad buy-in from all levels of government, cannot be phased like typical highway projects and must contend with a wide range of environmental factors.

MTC spokesperson John Goodwin said the project is "a smart investment to make sure the tunnel can keep connecting the East Bay for many more decades to come."

The tunnel first opened in 1937 with two bores. A third bore was added in the 1960s. Before the fourth bore opened in 2013, the center tunnel switched directions during peak hours to ease congestion.

Federal and state dollars are funding the project, drawn from the Infrastructure Investment and Jobs Act (IIJA), the federal infrastructure law Congress approved in 2021, and State Senate Bill 1, the Road Repair and Accountability Act of 2017. The Caldecott project is one of more than 150 California transportation projects sharing $2.7 billion in combined funding — $1.6 billion of it from IIJA and $542 million from SB1 — according to the East Bay Times.

The California Transportation Commission had tentatively scheduled a funding allocation for Aug. 21, and Caltrans listed a construction contract award for September. Caltrans said details on future closures, detours and traffic mitigation plans will be shared as the project advances. Residents seeking updates can contact Caltrans District 4 public information officer Hector Chinchilla at [email protected].

Caltrans has not announced a next public meeting date for the project.