TUNNEL CONSTRUCTION: Fourth is the charm California tunnelers
break through at Caldecott bore in the hopes of banning
congestion Tunnelers in California worked carefully forward
until, on Nov. 29, 2011, the crews from Oakland on the west end
and Orinda on the east broke through to form a continuous open
passage. They had to dig carefully, because the rock of the East
Bay Hills, separating Alameda and Contra Costa counties, is
fractured and requires support. The tunnelers were familiar with
the conditions, since this tunnel is the fourth bore of the
Caldecott Tunnel through the East Bay Hills to add lanes to S.R.
24. The first two bores—one for each direction of traffic—opened
in 1937. The third opened to traffic in 1964 and made it
possible to switch the direction of traffic in the middle bore
so four lanes were always available for the heavier traffic flow
and two lanes served the lighter flow. The fourth bore project
is a partnership between the Federal Highway Administration, the
California Department of T