Interpolis is the worst place to start with your transportation networks.
1. We don't really have an interpolis transportation problem in most of the US. You jump on the interstate everything is fine. We've got freight rail, barges, and air freight. You only run into congestion when your poleis have grown together like between Boston and DC or around the Bay Area.
2. Your interpolis transportation networks are useless without first having an intrapolis transportation network. If your system just dumps people or packages at a depot in each city, they won't bother using it in the first place.
3. You trade the political challenges of building in the cities for the engineering challenges of building thing hundreds of miles long and the political challenges of building things that go through dozens of municipalities without benefiting any of them.
All good points. But intrapolis also reduces the value quite a lot in a way. There's a lot less stuff I'd buy from my city or even wide local area. And local stuff can be brought by foot or bike (depending on weight and size of course). Still it could be pretty cool to be able to pack a thing and push it down a tube like cashiers uploading money in the 70s.
