The reference for locomotives and railcars


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Electro-Motive Division DD35, DD35A and DDA40X
United States | 1963 | 92 produced
DDA40X No. 6936 was preserved operational and is seen here in Union, Illinois in 2013
DDA40X No. 6936 was preserved operational and is seen here in Union, Illinois in 2013
H. Michael Miley

Since the gas turbine locomotives built for the Union Pacific in the 1950s did not manage to establish themselves as standard locomotives for very heavy trains, the development of particularly powerful diesel locomotives was tackled again in the 1960s. However, the power of the individual prime movers was limited, so it was decided to combine the power plants of two locomotives each on a common frame. Thus, there were two 16-cylinder series 567A, each with its own generator, on a frame, which in turn stood on two four-axle bogies

The first model was the DD35, which was built 30 times in 1963 and 1964, mainly for the Union Pacific. Their power plants were identical to those of a GP35, giving a combined output of 5,000 hp. They did not have a driver's cab and were intended for use as a B unit together with classic diesel locomotives. Since the four-axle bogies at the front of the train greatly reduced the service life of the rails, no A-units with a driver's cab were initially built. It was mostly used with two DD35s between two GP35s, giving a total output of 15,000 hp. It was not until 1965 that 15 DD35A cab-units followed, built exclusively for the Union Pacific. Both types had in common that the sandboxes were initially in the engine room and sand flying around caused problems in the electrical system there, which led to the sandboxes being relocated to the circulations.

The high point of the development of the eight-axle EMD locomotives were the DDA40X “Centennial”, of which 47 units were built between 1969 and 1971 for the Union Pacific. New 16-cylinder series 645 prime movers were now used, which brought the total output to 6,600 hp. Thanks to further developments on the bogies, it was no longer a problem if such a locomotive led the train. Inside, many new assemblies were used, which later came into other EMD locomotives. The driver's cab was of the wide design used on the FP45.

In day-to-day operation, however, it soon became apparent that such a powerful locomotive hardly brought any operational advantages compared to two smaller ones and was less flexible to use. For this reason, no further eight-axle large diesel locomotives were later developed, apart from special narrow-gauge machines with low axle loads. All later models had only four or six axles and were or are mostly used at least double-headed. Even today, when the current standard diesel locomotives have an output of more than 4,000 hp, trains with ten locomotives are formed on mountain routes. Also the already built DD35s and DD35As were phased out in the early 1980s and the DDA40Xs in the middle of the decade.

ManufacturerElectro-Motive Division
Axle configD-D 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length87 ft 11 in88 ft 2 in98 ft 5 in
Wheelbase72 ft 1 1/2 in82 ft 1 in
Fixed wheelbase17 ft 1 in
Service weight521,980 lbs519,353 lbs545,000 lbs
Adhesive weight521,980 lbs519,353 lbs545,000 lbs
Axle load65,248 lbs64,919 lbs68,125 lbs
Power sourcediesel-electric
Top speed90 mph80 mph
Starting effort113,940 lbf
EngineEMD 16-567D3AEMD 16-645E3
Engine type2x V16 diesel
Fuel5,200 us gal (diesel)8,230 us gal (diesel)8,280 us gal (diesel)
Engine output5,000 hp (3,729 kW)6,600 hp (4,922 kW)
Power Plant
Calculated Values
diesel locomotive
last changed: 03/2022

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