It sounds like something out of Jules Verne or The Jetsons, but in 1870 a "pneumatic subway" ran under Broadway in Manhattan. Built in secret so as to not to arouse the ire of Tammany Hall, only a block-long segment between Warren and Murray Streets was completed before an enterprising reporter for the New York Tribune exposed its existence.
"Let the reader imagine a cylindrical tube eight feet in the clear, bricked up and whitewashed, neat, clean, dry, and quiet," explained Scientific American in early 1870. The car itself fit snugly within the tube (there was an inch and a half clearance) and carried eighteen passengers at a cost of 25 cents each. "The weirdest thing about the subway project . . .," opined the New York Times in 1911, "is that the car was to be blown to and fro . . . by means of a big blowing machine." (In 1911, you could write things like that with a straight face.) The vacuum created when the air current was reversed pulled the car back in the opposite direction.
Over 400,000 New Yorkers took a joy ride underground during the three years the pneumatic subway was open for demonstration. But public enthusiasm couldn't protect inventor Alfred Beach and his Beach Pneumatic Railway from the wrath of Tammany Hall. Even though a bill proposing extension of the subway for the entire length of Broadway as originally planned was supported by state lawmakers, Governor Hoffman caved in to Tammany interests and vetoed the project. (In his exhaustive and fascinating history of the Beach Pneumatic Railway, Joseph Brennan suggests that Beach himself may have started the now-accepted-as-true story that Tammany Hall forced the closure of his railway.) When Beach finally gained approval in 1873 (after Tammany Boss Tweed's death and a new governor's inauguration), a stock market crashed killed financial support and thus the pneumatic subway.
In 1912, workers on the new BMT subway line reached Broadway and Warren Street, where they found the pneumatic railway tube, intact and well preserved. According to NYCSubway.org, the tunnel was almost certainly destroyed to make way for progress.