Voltage/Current

[Aristotle]

I have a question about electrical systems. I'm in Japan at the moment and have been taking a lot of trains, both high-speed and "local" (which is what non-high-speed trains are often called here, whether inter- or intra- city), and I notice that while the Shinkansen high-speed runs at 25kv AC, almost all locals run at 600-1500 v DC, and some of these locals are hitting around 80 mph. Both are mostly overhead catenary, including subway trains. I know that AC is more efficient for long-distance use, but given the difference in voltages, is it the case that motive power is mostly determined by current rather than voltage ?