The SD40T-2 is a model of diesel-electric locomotive built by General Motors Electro-Motive Division in the United States.

The SD40T-2 is equipped with a 16-cylinder EMD 645E3 diesel engine producing 3,000 horsepower (2,240 kW).

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.

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.