- an electric motor is dead simple and much cheaper than the mechanical complexity of an ICE (it's just a glorified spool of wire, attached to a fixed ratio gear. That's why Tesla can afford to slap a 2nd one on their 4-wheel drive vehicle (the xx"D" series), and that's why most european high speed train can afford electric motors on each of their wagon.)
Interestingly, not on TGVs which are among the most common high speed trains in Europe (470 trains). These trains have power cars at both ends.
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