Why Locomotives Can Pull So Much Weight

A single diesel-electric locomotive can pull 15,000 tons of freight across a continent — a feat that seems physically implausible until the engineering behind it is understood. Steel wheels on steel rails produce rolling resistance so low that the force required to keep a freight car moving on level track is a tiny fraction of its weight. The traction motors mounted on each locomotive axle convert electrical power from the diesel generator into rotational force applied directly to the rail, allowing a 400,000-pound locomotive to multiply its weight into tractive effort that no rubber-tired vehicle could approach. The locomotive doesn't fight the physics of moving heavy loads. It exploits them — and the efficiency margin it operates within is what makes the entire freight railroad system economically viable.