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 about 22 feet (6.7 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.