BART Tunnels and Tubes: Berkeley Hills to the Trans-Bay Tube

How this archive measures: lengths, bores, dates and ordering

How this archive is compiled

Each tube section has two bores 22 feet in diameter for train traffic separated by service tunnels in the middle, designated the upper and lower galleries. The upper gallery is a ventilation passage, with remotely controlled louvers connecting it to the train bores every third tube.The lower gallery has doors to the train bores at the midpoint of every tube, and contains a pedestrian/service cart passageway, small electrical substations, pump stations, etc.

The TBT is 135 feet below sea level at its deepest point. Basic tube construction was completed in 1969 after three years work, and was opened for Revenue Service in 1975. Construction cost was 180 million dollars.The seismic joint at the San Francisco Vent Structure moved 1/8 of an inch during the 1989 7.1 earthquake, it was designed for up to eight inches of movement. Thanks for your interest! This page was last modified on July 10, 2000

A tunnel list for the United States reads differently from a neighbouring country's, because the same journey time can be bought with one long bore in one country and a dozen short ones in another. Local spelling and official spelling diverge often enough that a list has to choose, and this one follows the operator.

A fault zone crossed at an angle is longer to pass through than the same fault crossed square, which is why alignments bend for reasons the map does not show. A short bore in a city can cost more than a long one in a mountain, because the expensive part is what sits above it.

This page records the structures catalogued for the United States in a tunnel almanac maintained at this address since the late 1990s. Tunnel building in the United States is shaped by geology and settlement pattern as much as by transport policy. Round numbers in an old list are usually estimates that hardened into record over time.

Reading the figures

Trade press reporting is faster than official publication and less reliable, which is why an opening date sometimes moves after the event. A record list is a snapshot of what was published, and its errors are usually inherited rather than invented. A tunnel's gradient is often the more interesting figure, particularly on subsea and base tunnels.

Ventilation type is recorded where known, because it constrains how long a bore can be built without intermediate shafts. Two crossings of the same length built fifty years apart are different objects, and only the number is comparable. Portals weather faster than the bore behind them, being the only part exposed to frost and sun.

Water under pressure is the single most disruptive thing a heading can meet, and it is rarely where the survey said it would be. The oldest crossings still in service were built before any of the design codes that now govern their maintenance. Where a structure has been lengthened by a later extension, the current figure is the one shown.

Switzerland's crossings are alpine and its practice is conservative, which shows in how few of its entries have ever been rebuilt. A hard shoulder inside a tunnel is expensive width, and its absence is why breakdowns are treated as emergencies. Reconstruction after a fire changes the ventilation and the escape arrangement, and often the recorded length as well. Toll revenue on a fixed link is usually pledged against the debt that built it, and the toll ends when the debt does.