From 1897 to 1953, New York City operated a pneumatic tube mail transport system. It consisted of 27 miles of tubing connecting 23 post offices and carried 95,000 letters per day, amounting to 30% of the city's mail volume. The canisters were two feet long and eight inches in diameter and could carry 600 letters.[1]
Jams were a bear. Crews would travel the route of the tube and check air pressure at test points every two blocks where the tube surfaced. When they found a drop in pressure at a test point, they would try to free the stuck canister by injecting extra pressure. If that failed, they would have to dig up the street.[2]
In the early 2000s, parts of the network were repurposed to run fiber optic cable.
Jams were a bear. Crews would travel the route of the tube and check air pressure at test points every two blocks where the tube surfaced. When they found a drop in pressure at a test point, they would try to free the stuck canister by injecting extra pressure. If that failed, they would have to dig up the street.[2]
In the early 2000s, parts of the network were repurposed to run fiber optic cable.
[1]https://en.wikipedia.org/wiki/Pneumatic_tube_mail_in_New_Yor... [2]https://hal.archives-ouvertes.fr/hal-01870447/document