The Caldecott Fourth Bore Project is a partnership between the California Department of Transportation (Caltrans), the Contra Costa Transportation Authority (CCTA) and the Alameda County Congestion Management Agency (ACCMA) to build a two-lane fourth tunnel bore north of the existing three Caldecott tunnels. The project is located on busy State Route 24 between Oakland and Orinda. The $420 million project will take approximately four years to build and also includes two smaller projects that will enhance traffic flow in the vicinity of the tunnels, as well as a future project to landscape the area once the tunnel project is completed.

With State Route 24 carrying about 160,000 vehicles per day traveling through the three tunnels, the new fourth bore will relieve congestion in the off-peak direction (eastbound in the morning and westbound in the afternoon), and eliminate the need to switch the direction of traffic flow in the middle bore to accommodate shifting traffic demands. When the Fourth Bore Project is completed, two bores will be permanently dedicated to westbound traffic and two bores to eastbound traffic.

The project is funded with federal, state and local funds (See Funding).

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Caldecott Fourth Bore Project on White House Blog