292 Union Pacific engines idled in Arizona Desert Total US rail traffic in April plunged 11.8% from a year ago, the Association of American Railroads reported today. Carloads of bulk commodities such as coal, oil, grains, and chemicals plummeted 16.1% to 944,339 units. - snip - Only five of the 20 commodity categories saw gains. Of the decliners, coal was the biggest. But petroleum products also plunged 25%, and grain mill products dropped 7%. Even without coal, carloads were down 3% year-over-year.