Total intermodal volume rose to 192,354 units, from 191,410 last year, AAR said in its weekly report.
Containers rose 3.2% to 162,729 units, while trailers fell 12% to 29,625 units.
Freight rail traffic, which excludes intermodal traffic, dropped 8.1% to 257,823 carloads, AAR said.
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.