The project is a partnership between Caltrans, the Contra Costa Transportation Authority and the Alameda County Congestion Management Agency. Funded with $197.5 million in federal Recovery Act dollars, $11 million in Proposition 1B monies, as well as other federal, state, regional and local funds, this project will reduce congestion on State Route 24 by building a fourth tunnel bore as part of the Caldecott Tunnel, linking Orinda to Oakland. Upon completion, the new northern bore and the existing northern bore will carry westbound traffic, while the two southern bores will carry eastbound traffic.

The new tunnel will be located to the north of the existing tunnels and have two 12-ft lanes, a 10-ft north shoulder, a 2-ft south shoulder, a 2-ft north emergency walkway and a 3-ft south emergency walkway. The new tunnel will be approximately 41 ft wide and 3,389 ft in length. Other elements of the project include seven emergency cross passages, a new two-story operations and maintenance building, construction of retaining walls and a noise barrier, pavement overlay at the State Route 24/Caldecott Lane interchange, improvements to eastbound State Route 24, realignment of the westbound Fish Ranch Road on-ramp, and improvements to the eastbound Fish Ranch Road on-ramp.