Looking at California: http://bit.ly/1eFevxA And Japan: http://bit.ly/19ZXwbJ I don't see any roads in Japan that are nearly as straight as I-5.
The places where this would make sense have destinations fairly far apart, but not too far apart, with somewhat amenable landscape between them. The Midwest would work, Australia, Russia. Probably Brazil, Argentina? Probably a bunch of connections in Africa or maybe the Mideast... but that wouldn't work for other reasons. East coast seems a bit cramped.
It is around 900km though, almost a straight line along the Hume highway and the busiest city-pair in Australia by a long way.
Sydney<->Melbourne is the third busiest air route in the world with 8 million passengers in 2012[1]. I'm sure there's more than enough "potential" passengers.
[1] http://en.wikipedia.org/wiki/World's_busiest_passenger_air_r...
Yes, 630+ km Hyperloop between Moscow and Saint-Petersburg would be a great project. Problems:
1. Winter. Would solar panels give enough energy during winter?
2. Highly-inflated cost due to corruption. I would speculate corruption is a big problem for California HSR too, given its cost.
3. "Russian Railways" company monopoly for all intercity railways in the country.