A covered hopper rolls through the computer-controlled retarders at East Hump while being sorted for eastern destinations at Union Pacific’s Bailey Yard in North Platte, Nebraska, on May 3, 2011. Retarders grip a cars wheels as they rolling off the hump, slowing the car through friction using a sophisticated system that considers car weight, distance the car must travel on a designated track, wind speed and direction and even air temperature.
