Trains traditionally use Direct Current (DC) primarily because DC motors offer superior starting torque and precise speed control, which are essential for moving heavy loads from a standstill. When a train starts, it needs a massive amount of power to overcome inertia, and DC motors handle this transition more smoothly than traditional AC motors. Historically, DC electrification (usually 600V to 3000V) was easier to implement for urban subway and tram systems because the infrastructure required less space and the motors were simpler to build. However, in 2026, while many older metro systems (like the NYC Subway or London Underground) still use DC "third rail" systems, long-distance high-speed rail has shifted toward AC (Alternating Current) because it can be transmitted over much longer distances with less energy loss. Even on these AC lines, modern trains often use "rectifiers" to convert the AC power back into DC for the traction motors, combining the efficient transmission of AC with the high-performance torque characteristics of DC.