A closer look
Sorting an avalanche of moving steel requires utilizing gravity as a weapon. Bailey Yard doesn't use individual locomotives to sort every single boxcar. Instead, a train is slowly pushed up a massive artificial mound called a 'hump'. As individual cars are uncoupled, gravity pulls them down through a complex web of branching tracks. Because a fully loaded coal car rolls much faster than an empty boxcar, computer-controlled pneumatic retarders built directly into the rails clamp violently onto the passing wheel flanges, precisely bleeding off kinetic energy so the cars gently bump together rather than exploding on impact.
