The Caldecott Tunnel Fourth Bore Project marked a significant milestone Tuesday afternoon when crews tunneling from its east and west sides broke through to meet in the middle, according to project spokeswoman Ivy Morrison.
The breakthrough represents a major accomplishment in the $390.8 million project that aims to relieve congestion on state Highway 24 between Orinda and Oakland.
Project officials said Monday that crews were just a few meters shy of breaking through and that the work was dependent on ground conditions within the tunnel.
Morrison said today that the excavating machine punched through the last barrier at about 2:45 p.m. Tuesday.
Crews have been excavating the top portion -- or the topheading -- of the fourth bore, although much more work lies ahead before the project is scheduled to be completed in late 2013, Morrison said.
The project is a partnership between the Federal Highway Administration, Caltrans, the Metropolitan Transportation Commission, the Contra Costa Transportation Authority, and the Alameda County Transportation Commission.