Hyperloop

[magnemoe]

17 hours ago, mikegarrison said:

It makes no sense to travel at high speed along the ground in thick air, when it is much more efficient to travel at high speed through the much thinner air at high altitudes.

Power required for a ground vehicle is approximately related to the velocity^3, while power needed for an airplane is approximately related to just velocity. (This is because the faster a plane flies, the more drag it makes but also the more lift it makes, which means the power required due to drag is compensated by a reduction in power required to provide lift. That's not the case on the ground.)

At low speeds, the ground vehicles are more energy efficient, but at high speeds the airplanes flying at altitude are more energy efficient.

The vacuum-train idea (which existed long before "hyperloop") is an attempt to get that benefit of lower drag without having to accept the cost of flying to high altitude. But it has its own costs, such as the energy it takes to maintain a vacuum in a tube that is hundreds or thousands of kilometers long.

This is true, but high speed trains negate some of the drag by being long still I think they will get problems because of drag an noise above 5-600 km/h, note this is turboprop speed, if you want to go supersonic you need an vacuum train. Hyperloop is not an vacuum train it uses small pods who would limit the capacity because of safety. You also need an large transport need but fast transport can create this or why highways get clogged up after major improvements. With rail you can make the train longer. So supersonic trains would have people living in Florida and commute to New York.