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For one construction project, the proverbial light doesn't come at the end of the tunnel, but rather at its middle.
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 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.