Caldecott Tunnel Fourth Bore

Congestion is recurrent on Route 24 for traffic traveling between Alameda and Contra Costa counties. The existing tunnel consists of two bores constructed in 1937 and a third bore, north of the original two, built in 1964. Each of the three bores has two mixed-flow lanes, reducing the freeway capacity at the tunnels from eight to six lanes. The primary objective of the Caldecott Tunnel fourth bore is to alleviate congestion in the off-peak direction where two tunnels will be permanently dedicated to each direction.

The Caldecott Tunnel fourth bore improves mobility for motorists and emergency crews along State Route 24 via the Caldecott tunnels; reduces delays and improves travel times; eliminates the need for daily tunnel reversals and lane merges; and enhances safety of the traveling public and Caltrans maintenance workers.

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