I recently learned that Hamburg had a big tube system ("Großrohrpost"). The tube diameter was 45cm and the length of the wagons was 1,60m.
Some information in the German Wikipedia: https://de.wikipedia.org/wiki/Rohrpost_in_Hamburg#Gro%C3%9Fr...
Recent article (paywalled) on German news site: https://www.zeit.de/2023/37/grossrohrpost-hamburg-kommunikat...