The problem is adhesion (lack of). Modern traction control systems (anti-slip) help quite a bit, but eventually you'll exceed what the steel-on-steel mating sur

The problem is adhesion (lack of). Modern traction control systems (anti-slip) help quite a bit, but eventually you'll exceed what the steel-on-steel mating surface can provide in terms of grip. Traditionally, you overcome this by using a heavier locomotive - which is one reason why the Union Pacific Big Boy was 1.2 million pounds (544,000 kg). It sounds like they're addressing this by making pretty much every car it's own locomotive. https://www.youtube.com/watch?v=0cd5Vcbi1gg https://www.youtube.com/watch?v=0cd5Vcbi1gg