The SD70 Series

EMD originally began as the Electro-Motive Corporation and has its beginnings in 1922 being based out of Cleveland, Ohio building inexpensive motorcars. With the purchase of the company in 1930 by General Motor, and more resources at its disposal the company began developing the precursor of the modern-day diesel-electric road unit (cabs and road-switchers), the streamlined trainset, which consisted of a powered car permanently attached to a few coaches (usually two or three cars). The most famous of these streamlined trainsets was the Burlington Zephyrs, a beautiful streamlined stainless steel creation (originally powered by Winton engines, which would also become a subsidiary of GM) that was extremely lightweight and fast. The original trainset, the Zephyr 9900, made headlines in 1934 when it completed a non-stop journey from Denver to Chicago in a little over 13 hours.

Because the power cars with these trainsets were permanently attached to the coaches EMC sought to design a locomotive free of this articulated setup but designed in such a manner that a railroad could still attach it to any passenger train and obtain the same, smooth streamlined look. This it did with the unveiling of the EA model in 1937, the first in a long line of passenger diesel locomotive designs that would come to be known as the E series.

Not surprisingly, soon after the EA unveiling the company decided to take things a step further and develop the first true diesel road unit, capable of pulling long freights in main line service. In 1939 it introduced the FT model (perhaps the key difference between the E and F series was that Fs rode on B-B trucks whereas Es rode on C-Cs and carried a noticeably longer carbody), the first in EMC’s F series and one of the most success diesel-electric designs of all time. The F series would go on to define American railroading for years and you can still see it in regular use today, over 60 years after it first debuted! The FT (which stood for Freight, Twenty-seven hundred horsepower) was a superb locomotive and although its 2,700 horsepower came from an A-B setup of a cab (A) and booster (B) units rated at 1,350 horsepower each, it was quickly loved by railroads for the efficiencies it held over steam such as its ruggedness and ease of maintenance.

The FT (which stood for Freight, Twenty-seven hundred horsepower) was a serious locomotive and although its 2,700 horsepower came from an A-B setup of cab (A) and booster (B) units rated at 1,350 horsepower each it would become embraced by the rail industry for the efficiencies it held over steam power as well as being rugged and easy to maintain.

Following the success of its cab units, EMD realized that there was a market to be made in the road-switchers, which at the time was mostly dominated by Alco with its RS series. Its first attempt at this type of locomotive, which gave the train crews both excellent vision all around the locomotive for switching and local service as well as enough horsepower to be used in main line operations, was the BL2. Although unsuccessful from a sales standpoint the BL2 was really a mere stepping-stone for its next model, the GP series (meaning General Purpose).

After relative failures with the SD50 and SD60 EMD finally got back on track with the SD70, which was released in 1992, albeit at the cost of having already lost first place in the market to GE. The locomotive featured EMD’s 16-cylinder 710G3B engine and was rated at 4,000 horsepower although that was not its biggest selling point. Learning from the failures of the earlier models EMD upgraded its computer systems and microprocessors to be more easily maintained and introduced perhaps the biggest selling point of all; new, radial trucks.

Featuring the HTCR truck (high-traction, six-axle, radial) it could steer itself into oncoming curves instead of just following the rail which greatly reduced wear to both rail and truck/axle components. Not surprisingly railroads absolutely loved such a feature, which perhaps more than other reason made the SD70 series so successful.

While the original SD70 model was only marginally successful (it only sold over 100 units) later releases, such as the SD70M, SD70MAC, and SD70I were extremely successful. Essentially there is little difference between the designs in terms of overall mechanics and layout.

The SD70M carries the new wide "safety" cab design (also sometimes called a comfort cab it is technically known as the North American Safety Cab) as the original SD70 was built with the Standard Cab purchased only by Norfolk Southern and Illinois Central (NS takes a particular liking to the Standard Cab and carries many in its fleet). The SD70M has, by far been the most successful SD70 design with over 1,500 built, most of these for Union Pacific who purchased over 1,400 of them!

The SD70I is similar to the SD70M in that its differing feature involves the cab. The “I” designation refers to the unit having an isolated cab (EMD calls it the Whisper Cab) from the main prime mover and other mechanical gear. Extremely quiet the feature works quite well although only a few dozen were purchased, all by Canadian National.

Across the industry the most successful SD70 has been the SD70MAC. The MAC carries the same wide-cab design as the SD70M except that it also features AC (alternating current) traction motors. Different from the traditional DC (direct current) traction motors AC is much more simple, reliable and easier to maintain albeit it costs far more. This added cost, however, has not deterred railroads and over 1,000 have been built mostly for CSX and BNSF Railway (BNSF’s predecessor Burlington Northern also purchased a few hundred of them).

The newest release of the SD70 is the SD70ACe (most in the industry simply call them SD70 “Ace” or “Aces.” Rated at 4,300 hp and carrying AC traction motors, looking similar to the SD80 and SD90 in terms of its flared rear radiator grill, the boxy-nosed unit is meant to comply with the EPA’s latest environmental regulations and since its debut in 2005 has been fairly successful with a few hundred of the units built to date.

Lastly there is also an SD70M-2 design, which looks virtually identical to the SD70ACe, and in reality is in virtually every way except for the name. They are given the “Dash 2” designation simply to differentiate them from the SD70M model but aside from this are identical to their sister SD70ACe. Norfolk Southern is the largest purchaser of the unit (over 100) with Florida East Coast, CN and others chipping in with a few more.

All in all EMD (today known as Electro-Motive Diesel as GM sold their locomotive division in 2005) has been very successful with the SD70 despite losing first place to GE and has now given their competitor stiff competition to its similar models the AC4400CW and new Evolution Series™.

In any event, while GE models are now as common as the SD40 series once was be on the lookout for the SD70 designs, there are o’plenty of them out there to spot, particularly the unique SD70ACe and SD70M-2s!

For more information on the SD70 series consider the book The American Diesel Locomotive from author Brian Solomon. The book studies everything from classic to newer diesel locomotive models. In all the book is a great resource and you shouldn’t be disappointed with it, not to mention that it is loaded with photos (many in color)!