Pacheco Pass Tunnel

The Pacheco Pass Tunnel is a planned tunnel to carry California High-Speed Rail across the Diablo Range in the vicinity of Pacheco Pass east of Gilroy, California. The tunnel will be the first mountain crossing constructed as part of California High-Speed Rail, connecting the San Francisco Bay Area and Central Valley portions of the system.

The tunnel is planned to consist of a pair of 28-foot (8.5 m) diameter tunnels. At 13 miles (21 km) long they are expected to become North America’s longest rail tunnels, surpassing the Mount Macdonald Tunnel in British Columbia. An additional 1.5-mile (2.4 km) rail tunnel is planned to be constructed to the west. The tunnels are expected to cost around $5 billion. The tunnel path runs parallel to the existing Pacheco Tunnel and Santa Clara Tunnel, two contiguous water tunnels connecting the San Luis Reservoir into Santa Clara County.

In 2004, two options were in consideration for the Diablo Range crossing: the Pacheco Pass option and a "direct" 31-mile (50 km) tunnel between San Jose and Merced significantly north of the Pacheco Pass. A route through the Altamont Pass even further north was also considered. In July 2008 the Pacheco Pass option was selected. The reasons were that the Altamont alignment would require the track to split west of the pass to serve different parts of the Bay Area, would require a new crossing of the San Francisco Bay using the Dumbarton Rail Bridge or a new bridge or tunnel nearby, and would require more homes to be seized by eminent domain. The Pacheco alignment however would require longer travel times to San Francisco, and being in a rural area leads to concerns of greater environmental harm.

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