That would replace one runway, but it still doesn&#x27;t compare to the number of planes that the sky can handle. Sky which is cheap&#x2F;free in comparison to building rails. There is definitely a point where trains are more efficient, particularly between a small number of large cities, but moving a large proportion of US air traffic onto trains, imho, is a different problem given the number of routes (1000s) and airports (100s).<p>I&#x27;d have to see the math, but there is also a question as to carbon emissions per-passenger&#x2F;distance.  I believe that on long flights (more time at high altitude) widebody aircraft might be more fuel efficient than high-speed trains stuck on tracks.