What do most trains run on? Aren't diesel electric trains very efficient?
I think all high-speed rail runs off of overhead electric catenaries. Amtrak's Acela Express does as well.
Shinkansen, TGV, ICE (Germany), CRH (China), KTX (Korea using TGV tech), Spain, THSR (Taiwan using Shinkansen tech), and Turkish (using CRH tech) high speed rail are all electric.
The UK's higher speed HST is diesel-electric, though HS1 and the upcoming HS2 are electric.
Maglev, of course, is all-electric, with the track providing levitation, propulsion, and onboard power via induction.
Diesel electric trains are very efficient, transferring between 30-35% of the energy of combustion to the wheels, but electric trains can be even more "efficient" in the sense that the electricity for their traction motors can be provided directly through the overhead catenary, so:
1. You can generate that electricity more efficiently in a large power plant, though you will have transmission losses. Combined cycle gas can run at 62% efficiency for base loads, plus you're running off of cheap natural gas. It's not worth getting into the operational efficiency of other power generation sources, but they could arguably have even lower operational/fuel cost.
2. The transmission from the catenary and through the transformers runs at 95% efficiency.
3. You don't have to haul around the diesel engine, electric generator, or the diesel fuel.
These efficiencies add up to a lot for high speed rail, where weight matters. I think the weight is less of a factor for freight trains pulling heavy loads, so we'll likely not see significant conversion of freight trains to electric for a long time.