Federal regulators said Friday that railroads need to re-examine how they assemble their trains after a string of derailments in recent years that were at least partly caused by the way empty and loaded cars were mixed together with locomotives.
Heavy cars at the back of a train can push and pull against empty cars in the middle of a train as it goes over hills and around corners. Those forces have become more of a problem as the industry increasingly relies on longer trains with a wide variety of freight aboard.
