A total of 312 units were built for three railroads in the United States between April 1974 and July 1980. This locomotive and the SD45T-2 are popularly called tunnel motors, but EMD's term is SD40-2 with "cooling system modifications" because they were designed for better engine cooling in mountainous areas.[1] The differences between the SD40T-2 and its non-tunnel motor cousin, the SD40-2, are the radiator air intakes are located lower down at the rear of the locomotive.
This locomotive model was purchased by the Denver and Rio Grande Western Railroad, the Southern Pacific Railroad, and its subsidiary Cotton Belt. Southern Pacific's version has a 4,400-US-gallon (16,700 L; 3,660 imp gal) fuel tank and is 70 feet 8 inches (21.54 m) long. Rio Grande's version has a smaller 4,000-US-gallon (15,100 L; 3,330 imp gal) fuel tank.
8300 series featured extended "snoot" noses for radio control equipment. 8278 was damaged beyond repair in the 1989 Cajon Pass runaway and sold for parts, then scrapped.