[elif]

As for direct GHG emissions, the most efficient mode of travel depends on many factors involving the models, occupancy, and route, but generally speaking, planes can become more efficient than trains for distances >= 700 miles.

[Transfinity]

Source: https://www.ucsusa.org/clean-vehicles/getting-there-greener

Turns out motor coaches (e.g. Greyhound busses) are the most efficient at pretty much any distance.

[morsch]

Their number for travel by rail: 0.37 - 0.43 pound of CO2 emissions per passenger-mile.

Germany's department of environment number for travel by rail: 38 gram/kilometer = 0.13 pound per passenger mile.

(Source (German): https://www.vcd.org/fileadmin/_processed_/8/9/csm_Emissionen...)

[lutorm]

Yeah, electrified rail is by far the most energy-efficient way of transportation. How that translates to CO2 emission of course depends on how the electricity is made.