Even the us high speed rail Association claims efficiency only up to ~1000 mile trips, and this is their own best case marketing claims. And they're fighting for the sub 125mph version using existing ROW.

http://www.ushsr.com/hsr/completesystem.html

This paper shows only about a 3% to 20% improvement in co2 per passenger mile by shifting air traffic to already existing hsr in Europe (200-800km trips, taking into account embedded energy, and assuming %50 will be recyclable, which I think is quite optimistic)

https://doi.org/10.1155/2018/6205714