An SD40T-2 is a 6-axle diesel-electric locomotive built by General Motors Electro-Motive Division having a 16-cylinderEMD 645E3diesel engine producing 3,000 horsepower (2,240 kW). 312 SD40T-2s were built for North American railroads between April 1974 and July 1980. This locomotive and the SD45T-2 are popularly called tunnel motors, but EMD's term is SD40-2s with "cooling system modifications" because they were designed for better engine cooling in tunnels. The difference between this locomotive and its non-tunnel motor cousin, the SD40-2, are the radiator intakes and radiator fan grills located at the rear of the locomotive. The radiator air intakes in this model were along the deck to allow more fresh, cooler air to enter and less hot exhaust fumes lingering around the tunnel's ceiling.
EMD SD45T-2 vs SD40T-2 radiator fan motor access doors
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) 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. After merging with Rio Grande, the Southern Pacific and later Union Pacific owned every SD40T-2.
In 2005, most of these units were owned by Union Pacific or leasing companies. By 2008, none were left in service on UP with SP or DRGW reporting marks. DRGW 5371 was the last one, retired in March 2008, and now resides at the Utah State Railroad Museum in Ogden Utah. UP still runs many units repainted in its own livery.