A concept
subway system in which a
cylindrical train car is propelled through a tunnel by air pressure. The
idea was
pioneered in 1870 by
Alfred Ely Beach, then editor of
Scientific American, who
financed the construction of an
experimental
pneumatic train subway that was about a
city block long and incorporated a huge
fan to generate air pressure. However, the
municipal authorities declined this system in favor of
elevated trains.
The idea was revived in the mid-19
60's by
Lockheed and
MIT in conjunction with the U.S.
Department of Commerce. The feasibility of such a system to connect cities was contemplated, particularly the
Boston-to-
Washington corridor. A few
enhancements to the original idea were conceptualized: Opening and closing
valves would allow
ambient air pressure to push the
cars and the tunnels would slope downward out of each
station to assist in the acceleration. It was calculated that on a run between
Philadelphia and
New York, the average speed might be as high as
390 miles per hour; about half of the
speed of sound.
The idea was largely scrapped due to the massive cost in boring the tunnels and removing the air within them. Furthermore, if there was a small
breach at any point in the tunnel that compromised the
vacuum, the entire tunnel would have to be shut down.