EMD DDA40X

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EMD DDA40X
Union Pacific 6922 on display at Cody Park, North Platte, Nebraska
Type and origin Power type Diesel–electric Builder General Motors Electro-Motive Division (EMD) Build date April 1969 – September 1971 Total produced 47
Specifications Configuration: ​  • AAR D-D  • UIC Do'Do' Gauge 4 ft 8+1⁄2 in (1,435 mm) Wheelbase Between truck centers: 65 ft (19.81 m) Truck wheelbase: 20 ft 1+1⁄2 in (6.13 m) Length 98 ft 5 in (30.00 m) Width 10 ft 4 in (3.15 m) Height cab roof: 14 ft 11+3⁄8 in (4.56 m) overall: 16 ft 4 in (4.98 m) Loco weight 545,000 lb (247,000 kg) or 260.99 short tons (233.03 long tons; 236.77 t) Fuel capacity 8,280 US gal (31,300 L; 6,890 imp gal) Prime mover 2 × EMD 16-645 Engine type V16 diesel Aspiration turbocharged Cylinders 16 Safety systems Leslie Supertyfon model S5TRRO or S3LR horns, US&S Type 'EL' Cab Signals (6936 equipped with US&S MicroCab ATC & CCS)
Performance figures Maximum speed 80–90 mph (129–145 km/h) Power output 6,600 hp (4,920 kW) Tractive effort starting: 113,940 lbf (506.8 kN) @25% continuous: 103,000 lbf (460 kN) @12 mph
Career Operators Union Pacific Numbers 6900 – 6946 Nicknames "Centennial" Delivered 6900-6924 April – December 1969 6925-6946 June 1970 – September 1971 Disposition 11 in museums, 1 operational, 1 pending disposition, 34 scrapped

The EMD DDA40X is a 6,600 hp (4,943 kW) D-D locomotive, built by EMD from 1969 to 1971 exclusively for the Union Pacific Railroad.^[1] It is the most powerful diesel–electric locomotive model ever built on a single frame, having two 16-645E3A diesel prime movers.^[2] Union Pacific has marked DD40X on the cab exteriors, while EMD literature inconsistently refers to this model as either DD-40X or DDA40X.^[3]

UP's DDA40X locomotives were the culmination of the company's experiments with extremely powerful locomotives that began with its gas turbine–electric locomotives and DD35s.^[4] For manufacturer EMD, the construction of the world's most powerful single frame locomotive was a sign of the company's dominance of the North American diesel locomotive market, with only GE Transportation an equal competitor. The DDA40X also pioneered a number of new technologies that would go on to be incorporated in future EMD designs.

Ultimately, UP did not continue with exceptionally powerful locomotives like the DDA40X built on single frames, instead moving toward distributed power using smaller locomotives closer to 4,000 hp. All of DDA40X locomotives were retired between 1984 and 1986; several of them survive. Union Pacific 6936 operated as a member of the Union Pacific Heritage Fleet until 2022, when it was announced it would be donated to the Railroading Heritage of Midwest America museum.^[1][5]