Beneath the streets of downtown St. Louis lie fragments of a once cutting-edge, now outdated mail system: the pneumatic mail system.
Though it had a short operational run, this technology was revolutionary in its day.
Origins of the Pneumatic Mail System
The idea began in Europe.
As early as 1853, the London Stock Exchange used a pneumatic mail system to quickly transmit stock prices and sales information to investors via telegraph offices.
By 1866, London was using a similar system to deliver mail.
Other European countries—including France, Italy, Germany, Ireland, and Austria—also adopted pneumatic mail.
Inspired by this, U.S. Postmaster General John Wanamaker initiated the first American pneumatic mail system.
Since the Post Office lacked experience with this technology, a private company was tasked to build and install the tubing system and power stations at no cost to the government.
The company would then lease the system to the U.S. Post Office and charge for its use.
The First Pneumatic Mail Systems in America
The Pneumatic Transit Company of New Jersey won the first bid.
In 1893, the first American pneumatic mail system was installed in Philadelphia, running from the General Post Office to the Eastchester Post Office.
Philadelphia expanded lines connecting railway stations to post offices.
Soon after, Boston, New York, and Chicago followed with their own systems.
What is a Pneumatic Mail System?
A pneumatic mail system is an underground network of vacuum-sealed tubes connecting sending and receiving stations.
Tubes were made of cast iron, about 8 inches in diameter, buried 4 to 8 feet underground depending on the city’s terrain.
Joints were leaded for airtight seals; when closed, tubes were secured with bolted flanges.
Mail traveled inside canisters:
About 7 inches in diameter and 22 inches long.
Weighed roughly 20 pounds empty.
Had lockable doors on each end and four wheels for smooth travel.
Could hold around 500 letters or postcards.
Fans and pumps propelled canisters through tubes using air pressure between 3 to 8 psi, reaching speeds up to 30 mph.
At full capacity, the system could transport 200,000 letters per hour.
Operation and Maintenance
Post office employees called rocketeers operated the systems.
Power stations featured rotary blowers and air compressors powered by electric fans.
Telephone lines connected offices for communication.
Maintenance included periodically sending an oil-filled canister through the tubes to keep them lubricated—something that sounds like a recipe for disaster but worked nonetheless.
If you want a mental image, think of the pneumatic tube systems banks use to send cash and documents.
In fact, it reminded me of the Paddington movies, where miles of pneumatic tubes send information requests inside the Geographer’s Guild building. (If you haven’t seen them, you really should!)
Pneumatic Mail in St. Louis
St. Louis was the last—and fifth—U.S. city to install a pneumatic mail system.
In 1900, the St. Louis Manufacturers Association formed a committee to push for the system, aiming to have it operational by the 1904 World’s Fair.
Congress approved funding on April 21, 1902, for 3.16 miles of double tubing in downtown St. Louis.
The St. Louis System
Two main lines were installed:
From the Post Office Annex at 18th and Clark (behind Union Station) to the General Post Office at 9th and Olive. This line carried mail arriving by train for processing.
From the General Post Office to a relay depot near the west end of the Eads Bridge on the Missouri side. The original plan to extend to East St. Louis depended on Eads Bridge repairs, which became unnecessary after railroad rerouting.
Operation Schedules
The main line operated seven days a week:
Monday-Saturday, 4 AM to midnight.
Sunday, 7 AM–11 AM and 4:30 PM–8:30 PM.
The bridge line ran seven days:
Monday-Saturday, 6 AM to 7 PM.
Sunday, 7 AM to 11 AM only.
Challenges and Decline
The system worked fairly well except during peak hours (7–9 AM), when mail volume overwhelmed it—causing delays up to two or three hours.
A 1916 Congressional report recommended not renewing pneumatic mail contracts except for Boston and New York.
Despite efforts by St. Louis business leaders to save their system, it closed permanently in 1917.
By then, trucks and vans were far more efficient for mail delivery.
Why Did the System Fail?
Congress cut federal funding in 1917, viewing the system as an “exorbitant, unjustified, and extravagant waste of public funds.”
Operation costs ran about $17,000 per mile annually (approximately $390,000 per mile today).
With New York alone having 27 miles of tubes, costs ballooned.
The system only handled postcards and letters—packages still required traditional delivery.
It was prone to mail loss and damage, and a single tube problem could shut down entire lines.
Legacy of the Pneumatic Mail System
Despite its flaws, some cities privately funded pneumatic mail systems well into the 1950s.
For St. Louis, the system was never ideal:
The main line ran at about 26% capacity.
The bridge line operated at about 4% capacity.
St. Louis was the smallest and least congested city to install pneumatic mail tubes.
Though brilliant for its time, rapid mail volume growth and the rise of the automobile made the pneumatic system obsolete.
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Until next time, I’ll see you in the Lou.