 This philosophy helps to explain why the D&RGW, despite its proximity to one of the nation's most productive coal mining regions, retired coal-fueled steam locomotives as quickly as new, replacement diesels could be purchased.By 1956, the D&RGW's standard-gauge steam locomotives had been retired and scrapped.The reason for this was that unlike steam locomotives, diesel locomotives could easily be combined, using the diesels' multiple unit capabilities, to equip each train with the optimum horsepower which was needed to meet the D&RGW's aggressive schedule.