 In time, the D&RGW's fast freight philosophy gave way to SP's long-established practice of running long, slow trains.A contributing factor was the rising cost of diesel fuel, a trend that set in after the 1973 oil crisis, which gradually undermined the D&RGW's fuel-consuming "fast freight" philosophy.By the early 1990s, the combined Rio Grande/Southern Pacific system had lost much of the competitive advantage that made it attractive to transcontinental shippers, and became largely dependent on hauling the high-quality coal produced in the mine fields of Colorado and Utah.