The Secret History of the St. Louis Post Office and Its Amazing Pneumatic Tube


A tube room in the basement of a post office. It's unclear where this particular tube room was, but if it wasn't in St. Louis, the one here probably looked very similar. - IMAGE VIA
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  • A tube room in the basement of a post office. It's unclear where this particular tube room was, but if it wasn't in St. Louis, the one here probably looked very similar.

One hundred years ago, subterranean St. Louis was a fascinating place. There was, of course, the web of caves that stretched from Benton Park north to downtown and east to the Mississippi River with detours into neighborhood basements. Before the Civil War, the cave network may have been one of the the last stops on the Underground Railroad before Illinois and freedom, but by the turn of the twentieth century, it was mostly used by local breweries to store beer and was -- and remains -- a subject of fascination for urban explorers.

Less well known, maybe because it was too small for people to crawl through, was the system of pneumatic tubes that spirited mail from Union Station to the Old Post Office on Ninth Street and back again.

Pneumatic tubes have, sadly, gone out of fashion, except at drive-through banks, nuclear reactors, Denver International Airport and, allegedly, the British House of Commons, but at the end of the nineteenth century, they were considered cutting-edge technology, an easy way to move money, letters and small packages within buildings. But a few early proponents of pneumatic tubes, including Alfred Ely Beach, the editor of Scientific American in the 1860s and '70s, had much grander ambitions.

In 1867 in New York City, Beach demonstrated an underground Pneumatic Railway, large enough to hold twelve passengers at a time. In contemporary illustrations, it looked pretty steampunk-fabulous.

Sadly, the idea was expensive and never really caught on. Within twenty years, engineers had figured out a way to build trains that ran through a tube underground without producing exhaust that would suffocate the passengers: the subway!

Still, the fascination with pneumatic tubes remained.

A map of the St. Louis pneumatic tube system. - IMAGE VIA
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  • A map of the St. Louis pneumatic tube system.

(If you've ever been at the bank and watched the little capsule with your deposit slip fly upward through a tube, you'll understand.) Since 1853, a series of tubes had ferried mail and telegrams beneath London's congested streets; it was, the post and telegraph offices found, much quicker and more convenient than hauling letters around in a horse-drawn cart or relying on fleet-footed human messengers.

In 1893, the U.S. Postal Service decided that the Londoners (and, by then, Parisians and several cities' worth of Germans) were onto a good thing and decided to test half a mile of pneumatic mail tube in Philadelphia. Within five years, Boston, New York and Brooklyn all had their own pneumatic tube systems. St. Louis didn't get one until 1905, a year after Chicago. It was to be the last and the least of the U.S. systems.

St. Louis's tubes ran a little less than two miles; by contrast, New York's system, the largest in the U.S., was 27 miles, not counting the tube that ran under the East River to Brooklyn. It was also the least efficient: Most of the time, the tubes, which were open from 4 a.m. to midnight six days a week, ran at only 26 percent capacity, except between 7 and 9 a.m. when the two big mail trains arrived. Then it was overwhelmed and the mail would be delayed for as long as 20 minutes. That was about five times as long as it took normally for the capsules to whiz their way from the train station to the main post office.

The tubes themselves were eight inches in diameter. The capsules were seven inches in diameter and 22 inches long; they could each hold about 600 letters. They didn't look much different from the capsules that are still used in banks. (Why mess with good technology?) Underground, they traveled at 30 miles per hour, propelled along by a system of fans and pumps that would either blow them forward or suck them backward.

Unfortunately for the St. Louis pneumatic tube system, it debuted at almost the exact same time as the automobile. It took a few years for cars to be able to move as fast as the tubes. But in 1916 the U.S. Postal Service did a cost/benefit analysis that came down very heavily on the cost.


1. High rate of speed between stations for limited quantities of mail. 2. Freedom from surface congestion.

Limitation and disadvantages:

1. Only five pounds of mail could by carried in each container; and all classes of mail could not be carried. 2. The minimum time between dispatches is 15 seconds allowing only 20 pounds of letter mail each minute. Therefore, vehicle service would be required to carry mail during heavy volume times. 3. The inability to carry special delivery parcels due to the size of the carriers. 4. The relays at station are built in delays but they are unavoidable requiring all stations to be manned and open during operation. 5. The inability to dispatch between intermediate stations during continuous transmission between any two points. 6. Inability to dispatch to railroad companies without additional handling. 7. Complaints resulting from careless locking and accidental opening of container in transit causing damaged mail. 8. Dampness and oil damage to mail. 9. Service interruptions block an entire line. 10. Congestion from heavy mail volumes. 11. Equipment takes up rented building space. 12. Excessive costs.

An actual piece of mail that had traveled (unsuccessfully) through the St. Louis pneumatic tube system. - IMAGE VIA
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  • An actual piece of mail that had traveled (unsuccessfully) through the St. Louis pneumatic tube system.

The excessive costs -- $17,000 annually per mile of tube -- were probably the tipping point. The pneumatic tube system was doomed. Within the year, it had been phased out of four of the five U.S. cities; New Yorkers got to keep theirs until 1953 because of their trans-river traffic.

The pipes probably still exist, though these days they wouldn't be particularly useful, given that the Old Post Office is an office building and Union Station is a mall.

Still -- just imagine if the masterminds behind the pneumatic tube system, namely Charles Emory Smith, who was postmaster general at the time the tubes were installed, had gotten their way and we all got our mail by tube. Would it still be as cool? Or would we be as unimpressed as Winston Smith in the opening pages of Nineteen Eighty-Four?

h/t John Schranck