U.S. intermodal traffic slipped 0.4% for the week ended Saturday from a year ago, the Association of American Railroads reported.
Container traffic rose 2% to 197,495 units, but trailer traffic plunged 13.7% to 29,712 units.
Railroad carloads excluding intermodal rose 1.7% to 279,501 units, the rail trade group said in its weekly report.
Railroad volume is considered an important economic indicator. Intermodal traffic, which tends to be higher-valued merchandise than bulk commodities, uses trains for the long haul and trucks for the shorter distance at either end of the trip.