U.S. crude-by-rail shipments dipped nearly 17% in 2015 as domestic crude oil production slowed, according to the Association of American Railroads. Railroads moved 410,249 carloads of U.S. crude last year, compared with 493,146 in 2014. Railroads struggled last year as plummeting commodity prices — particularly those of oil and coal — hurt volumes. Total traffic for the year dipped 2.5% to nearly 28 million carloads, trailers and containers, according to the AAR. Oil producers have cut back on drilling wells domestically as energy prices fell, resulting in a declining number of carloads. Even so, crude by rail is still just a fraction of total shipments, accounting for 1.4% of carloads last year, compared with 1.6% in 2014. Crude-by-rail carloads fell by 35.2% in the fourth quarter compared with the same quarter a year earlier.