Berkeley Hills Tunnel

The Berkeley Hills Tunnel is a tunnel which carries Bay Area Rapid Transit's Pittsburg/Bay Point–SFO/Millbrae line through the Berkeley Hills between the Rockridge and Orinda stations. While the tracks run in the median of California State Route 24 on both sides of the tunnel, the Berkeley Hills Tunnel allows the tracks to take a straighter alignment offset to the north of the Caldecott Tunnel.

It bores through the Berkeley Hills east of Berkeley and Oakland a distance of 3.2 miles (5.1 km) through a variety of rock strata, most of which are soft and porous. The earthquake-active Hayward Fault bisects the tunnel about 1,000 feet (300 m) inside the west portal (Oakland side). There are 2 bores, each 17.5 feet (5.3 m) in diameter, spaced 50 feet (15 m) apart. Pedestrian cross-tunnels are spaced every 1,000 feet (300 m) for emergency evacuation in case of fire, etc. There is a ventilation structure at the east portal with roll-down doors that can close off the tunnel end to allow air to be sucked out or blown in. Boring was completed in February 1967 after 465 work days. The tunnel was opened for revenue service in 1973.

Material removed in the construction of the tunnel was used as fill for a concurrent expansion of the Port of Oakland.

On December 4, 2013, a BART train suffered mechanical braking problems and made an emergency stop in the Berkeley Hills Tunnel near Rockridge station. Eleven people were treated for smoke inhalation.