WASHINGTON (AP) â¿¿ Traffic on freight railroads rose 7.5 percent in March, the first rise since July 2008, an industry trade group reported Wednesday. The Association of American Railroads said shipments compared with March 2009 rose for 16 out of 19 commodities it tracks. That included increases of 66.1 percent for primary metal products, 20.4 percent for grain and 15.5 percent for chemicals. The group noted that volume was still down 11.5 percent from March 2008. Seasonally adjusted carloads rose 3.9 percent from February. The shipment of truck trailers on rail cars, called intermodal traffic, rose 2.1 percent. Intermodal traffic was up 12.1 percent compared with March 2009.