|This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (August 2008)|
UP DDA40X #6922 at Cody Park; North Platte, Nebraska.
|Type and origin|
|Builder||General Motors Electro-Motive Division (EMD)|
|Build date||April 1969 – September 1971|
|AAR wheel arr.||D-D|
|Gauge||4 ft 8 1⁄2 in (1,435 mm)|
Between truck centers: Script error: No such module "convert".|
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|Length||Script error: No such module "convert".|
|Width||Script error: No such module "convert".)|
cab roof: Script error: No such module "convert".|
overall: Script error: No such module "convert".
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|Fuel capacity||Script error: No such module "convert".|
|Prime mover||2 × EMD 645E3A|
|Engine type||V16 diesel|
|Power output||Script error: No such module "convert".|
|Safety systems||Leslie Supertyfon model S5TRRO or S3LR horns, US&S Type 'EL' Cab Signals (#6936 equipped with US&S MicroCab ATC & CCS)|
|Number(s)||6900 – 6946|
|Nicknames||"Centennial", "Big Jack"|
6900-6924 April – December 1969|
6925-6946 June 1970 – September 1971
|Disposition||1 in service, 46 withdrawn, (13 preserved, 34 scrapped)|
The DDA40X was a Script error: No such module "convert". D-D diesel-electric locomotive built by the General Motors EMD division of La Grange, Illinois for the Union Pacific Railroad. Nicknamed "Centennial" and "Big Jack", the DDA40X uses two diesel engines (each Script error: No such module "convert".) and is the most powerful single-unit diesel locomotive ever built, although more recent locomotive designs such as the GE AC6000CW, EMD SD90MAC and the China Railway DF8C have come close. It is also the longest single-unit diesel locomotive ever built.
In 1969 Union Pacific was retiring the later gas turbine-electric locomotives. Union Pacific had ordered EMD DD35s and DD35As to replace the turbines, and the DDA40X was a further development. Forty seven were built between June 1969 and September 1971, except the first one delivered in April in time to participate in the celebrations of the centennial anniversary of the completion of the Transcontinental Railroad driving the "Gold Spike Limited" and arriving in Salt Lake City, Utah, on the morning of May 10, 1969. The units were numbered from 6900 to 6946, with 6936 still in service.
The DDA40X is Script error: No such module "convert". long. The frames were fabricated by an outside contractor, the John Mohr Company of Chicago, since the frame length exceeded the abilities of EMD's plant. Using more than one prime mover in a single locomotive was not new; the E-series were popular dual-engine locomotives, and Baldwin had produced (but not sold) a locomotive with four diesel engines.
The 'X' in the designation stood for eXperimental, as the DDA40X locomotives were used as the testbeds for technology that would go into future EMD products. The modular electronic control systems later used on EMD's Dash-2 line of locomotives were first used on the DDA40X. The locomotive was the first to be able to load-test itself using its dynamic braking resistors as an electrical load so that external equipment was not required. The DDA40X used the wide-nosed cab from the FP45 cowl units. This design was superficially similar to the Canadian comfort cab introduced by Canadian National soon afterwards in 1973, but it lacked the structural reinforcements introduced in the CN design that were carried over to future wide-nosed cabs.
As the DDA40X program was a test, a number of experiments were conducted during the service life of these locomotives. One such test included fitting a few of the units with air raid sirens to warn track-side personnel when away from grade crossings, but the results were inconclusive. Another of the tests included successful modular electrical components. This made for easier diagnosis of electrical problems. These modifications were used in all future locomotive units built by EMD. All DDA40X units included a new load test circuit, allowing units to load test without a track-side load test box. Gearing was 59:18, allowing 80 mph on passenger trains.
By 1974, averaging 22,000 miles a month, most DDA40X units had run over 1,000,000 miles and needed more maintenance.  Union Pacific retired fifteen inoperable DDA40Xs in June 1984 to extract parts for the operating units, and all retired by the end of 1986. Number 6936 however is still in service with UP, though mostly in excursion service.
|Union Pacific Railroad||47|
- 6900 - Kenefick Park, Omaha, Nebraska
- 6901 - Ross Park, Pocatello, Idaho
- 6911 - Mexico Museum of Technology, Mexico City
- 6913 - Museum of the American Railroad, Dallas, Texas
- 6915 - Southern California Chapter, Railway and Locomotive Historical Society, Fairplex, Pomona, California
- 6916 - Utah State Railroad Museum, Ogden, Utah
- 6922 - Cody Park, North Platte, Nebraska
- 6925 - Stored at Chamberlain, South Dakota, on Dakota Southern Railway
- 6930 - Illinois Railway Museum, Union, Illinois. Used as a control cab only, engines and motors are currently non-operational.
- 6936 - Still in service with Union Pacific Heritage Fleet
- 6938 - North Little Rock, Arkansas (Sits in front of Jenks Locomotive Facility)
- 6944 - Museum of Transportation, St. Louis, Missouri, sent to Altoona in July 2014 for cosmetic restoration
- 6946 - Western Pacific Railroad Museum, Portola, California. The last DDA40X built. This locomotive is fairly complete and on static display.
|40x40px||Wikimedia Commons has media related to EMD DDA40X locomotives.|
- Don Strack. "Utah Rails DDA40X page". Utahrails.net. Retrieved 28 January 2015.
- CN Locomotive Cab Layout GR-20c, Commission of Inquiry Hinton Train Collision, December 1986
- "Union Pacific Centennials". Steamlocomotive.com. Retrieved 19 November 2014.
- Union Pacific Railroad Locomotive Department (1979). Locomotive Diagram Book. Union Pacific Railroad Company.
- Union Pacific Railroad Locomotive Department (1994). Locomotive Diagram Book. Union Pacific Railroad Company.
- Hayden, Bob (Ed.) (1980). Model Railroader Cyclopedia-Volume 2: Diesel Locomotives. Kalmbach Books. ISBN 0-89024-547-9.