U.S. intermodal shipments by rail grew 6.4% in the week ended Dec. 21 compared with the same week last year, the Association of American Railroads reported.

Traffic grew to 255,456 units, AAR said in its weekly report issued Dec. 26.

Rail carload traffic, which excludes intermodal, dropped 0.3% to 289,528 carloads, according to AAR. Half of the 10 commodity groups AAR tracks increased in volume.

So far this year, U.S. railroads have moved 12,659,296 intermodal units, a 4.5% increase over 2012. Last week’s AAR report showed that intermodal volume had already set a record for the year with two weeks remaining.