> the three dimensional world of aircraft. No, that's not how it works. En route airways are 3d, but approaches are 2d and landings are 1d. Large US airports

> the three dimensional world of aircraft. No, that's not how it works. En route airways are 3d, but approaches are 2d and landings are 1d. Large US airports are already at capacity, and above capacity in poor visibility conditions (like fog at SFO.) Also, trains can just add more engines and cars.