US is far from finishing deveping, fortunately or unfortunately. Take trains, for example, area where US is far behind China, Japan, or European countries, despite the size of its territory. I'm sure there are other examples.
The problem with infrastructure spending isn't that it doesn't potentially have a good ROI, it is that the process channels the money to wasteful projects that don't have a good ROI.
This is what happens in every ecosystem as the available energy sources become fully exploited. Featherbedding and cronyism are the parasitic vines which strangle enough trees so that when the next lightning strike comes the conflagration is inevitable. They cannot exist without the forest. When the forest grows to maturity they become inevitable.
So are Japan's. The idea isn't to get a profit off of tickets vs operating costs. The idea is to improve the efficiency of the country and economy. It's an investment.
If the US had a similar political climate the east coast would already have high speed rail from New York to Miami.
But they don't need to be, really, when they can just put it on a boat for the whole journey, or most of the journey and then just truck it a few hours inland.
