"The Intertubes" by paulgrahamraven

This too is an interesting idea. I have seen air-powered transport tubes at the local wholesale store - a Costco - which uses small, less-than-6-inch diameter pipes to transport certain small items. It would be wonderful to extend such a system to the local, metropolitan level. After all, mail only weighs a fraction of the vehicle carrier's weight, even when the mail truck is full. What sort of size range would this system be expected to encompass? Would each city have its own gauge or internal diameter specification for pipe?