U.S. intermodal traffic climbed 6% for the week ended Saturday from a year ago, the Association of American Railroads said.

Trailer traffic fell 9.3% to 29,782 units, but containers rose 8.7% to 209,494 units, the rail trade group said in its weekly report.

Railroad carloads excluding intermodal declined 3.6% to 282,262 units, the group 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.