The Caldecott Tunnel is getting a $267 million overhaul, its biggest in more than a decade. Construction starts in November and will last three years, reshaping the daily commute for Walnut Creek residents who use State Route 24.

The project will upgrade ventilation systems in three of the tunnel's four bores, replace structural pavement, overhaul drainage systems and install LED lighting, Gov. Gavin Newsom's office announced on Aug. 28. The Caldecott carries more than 160,000 commuters daily along SR-24 through the Oakland and Berkeley hills, connecting Contra Costa and Alameda counties.

The renovation is part of a $2.7 billion package the California Transportation Commission (CTC) approved for more than 150 projects statewide. Nearly $1.6 billion of that total comes from the federal Infrastructure Investment and Jobs Act of 2021. Another $542 million comes from California's Senate Bill 1, the Road Repair and Accountability Act of 2017.

Caltrans plans to replace fans in the three oldest bores with jet fans better equipped to manage smoke in case of a fire, the East Bay Times reported. The new fans will also improve everyday airflow.

To limit disruptions, at least two bores will remain open at all times during construction, one in each direction, the East Bay Times reported, citing the project's environmental document. Some work will take place during evenings and weekends. Specific lane-closure schedules and detour routes have not been released.

"The Caldecott Tunnel has always been a very critical, vital transportation link between Contra Costa County and the rest of the Bay Area," said Amy Worth, former Orinda mayor and former Metropolitan Transportation Commission chair. "I am really grateful for Caltrans … it is joyous news that this is in the budget and will be moving forward."

The tunnel first opened in 1937 with two bores. A third bore opened in the 1960s. Before the fourth bore opened in November 2013, traffic in the center tunnel switched directions during peak hours to ease congestion. That fourth bore cost $417 million, according to former Congressman Mark DeSaulnier.

Metropolitan Transportation Commission spokesperson John Goodwin called the renovation a smart investment to keep the tunnel connecting the East Bay for decades.

Caltrans has said it will share traffic mitigation details as the project moves forward.