"Can be" versus "Isn't".
Yes, HSR and its cousins can be run via alternative sources. But then again, for the time being they are not, and will likely not be for the foreseeable future.
Also, note that one of the most carbon efficient modes was the lowly diesel-powered bus. Even gasoline-powered personal autos were competitive. Alternate technology personal automobiles would be more efficient in comparison when they become more viable.