sentences:  Most British freight trains are one-man- or driver-only-operated, but certain freight trains do have guards on board for operational or safety reasons (such as DRS nuclear trains).According to the Federal Railroad Administration, one-man operated freight trains are "very rare" in the United States because it is hard to comply with federal safety regulations with only one person on the train.In the wake of the Lac-Mégantic derailment in July 2013, Federal Railroad Administrator Joseph C. Szabo demanded that Montreal, Maine and Atlantic Railway start using two-person train crews in the US.