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-1960'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.