How One Locomotive Engine Moves Millions of Pounds Across America Daily

A modern freight locomotive weighs around 200 tons and produces roughly 4,400 horsepower. A loaded semi-truck weighs 40 tons and runs on about 600 horsepower. The locomotive has seven times the engine output. Yet it routinely pulls 18,000 tons behind it. A truck pulls maybe 40. Why does seven times the power translate into 450 times the load? Why does adding more horsepower to a truck not get you anywhere close to that number? Something else is happening here. Something that has nothing to do with the engine.