Plotting (can't be all straight), air density (as mentioned by jessridel). Current high speed trains go at 180-200 mph due to sharply increased consumption abov

Plotting (can't be all straight), air density (as mentioned by jessridel). Current high speed trains go at 180-200 mph due to sharply increased consumption above those speeds, even though they could go a lot faster in current setups. In 30 years we'll probably have more efficient airplanes, and less fuel, so higher prices. Maybe it's more expensive in the short term, but it's much more sustainable to have ground-based transportation for trips under 400 or 500 miles. In Spain, we have the Madrid-Barcelona route. It's 50 minutes by plane and 2h30 by train (620 km, 385 miles). Airports are outside cities, stations are in the center of them and very well connected by road and commuter trains from everywhere. It's gone from being one of the busiest air routes to losing more than half of its traffic to high speed train. Why? Much more comfortable and, in the end, takes the same time.