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The Alco RSD4

(Please note that the Alco models featured on this page are not RSD4s.)

The Alco RSD4 was the builder's fourth installment of its six-axle Road Switcher (RS) series built at the same time as the RS3. Essentially, the design was a C-C version of the RS3 (Alco had also produced an A1A-A1A RSC3). Unfortunately, it was one of the least successful with fewer than 50 produced by the time production had ended (the manufacturer, however, only offered the design for a few years). Perhaps most notable with the RSD4 was the incredible tractive effort it offered, by far the most of any RS model up until that time. Unfortunately, railroads still had yet to embrace the six-axle concept, which was another reason for the design's poor sales (not even EMD could sell many six-axle units at the time). Amazingly, today at least one RSD4 remains preserved, and operational, Kennecott Copper Corporation #201 (the only RSD4 the company ever owned).

The Alco RSD4 line was built for two years, between 1951 and 1952 during the run of the RS3. The RSD4 featured the standard Alco 244 prime mover of the time allowing for 1,600 horsepower. As with the original six-axle model, the RSD1, the RSD4 was meant to provide a sizable increase in tractive effort and be used on light branch/secondary lines allowing the locomotive's weight to be distributed more evenly over additional axles. The Alco RSD4 had a slight design flaw as there was insufficient space for the unit's main generator, which was corrected with the RSD-5 that featured a longer hood and carbody. Consequently, the RSD-5 sold much better than the RSD4 with nearly six times more units produced.

(The above video clip depicts a scaled model of the RSD4 in service on the Utah Railway when it operated Alcos.)

One important historical note about Alco RSD4. From a technical standpoint, the model was the very first C-C model (meaning all six axles were powered) that Alco offered in its catalog. The RSD1 was merely a specialty order for the US Army and the RSC-2 and RSC-3 were, of course, A1A-A1A designs (meaning that the center axle was not powered). With the RSD4's six traction motors the model could produce a starting tractive effort rating of 89,000 pounds and 78,750 continuous. This was nearly a 33% increase over the RSC3 which could produce 60,100 pounds starting tractive effort and 52,500 continuous.

Internally, the RSD4 was supplied with parts from General Electric (its model 752 traction motor) and Westinghouse (air brakes and compressors). It kept the same frame as the RS3, remaining at a length of 55 feet, 11 inches. However, the one striking difference in the model, aside from its six axles was the weight; at 180 tons the RSD4 weighed nearly 70 tons more than the RS3 (of course, this weight also added to its tractive effort). The five railroads that ultimately did purchase the RSD4 used them as intended, in heavy freight service. This include the Atchison, Topeka & Santa Fe Railway, Utah Railway, Central Railroad of New Jersey, Kennecott Copper, and the Chicago & North Western Railway.

For a total production roster of Alco RSD4s please click here. For technical data on the model please click here. Finally, for more information about the RSD4 and all RS series designs please refer to the chart below.

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RS Series

Model Type	Units Built	Date Built	Horsepower
RS-1	417	1941-1960	1,000
RSD-1	257	1942-1946	1,000
RS-2	469	1946-1950	1,500-1,600
RSC-2	81	1946-1950	1,500-1,600
RS-3	1,370	1950-1956	1,600
RSD-4	36	1951-1952	1,600
RSD-5	204	1952-1955	1,600
RSD-7	29	1954-1956	2,250-2,400
RS-11	426	1956-1964	1,800
RSD-12	161	1956-1963	1,800
RSD-15	87	1955-1960	2,400
RS-27	27	1959-1962	2,400
RS-32	35	1961-1962	2,000
RS-36	40	1962-1963	1,800

For a comprehensive look at the American Locomotive Company and all of the motive power types it built from steam, diesel, to electrics consider the book Alco Locomotives by Brian Solomon. Covering more than 175 pages Mr. Solomon's book details the history of Alco from its esteemed 4-6-4 Hudsons and 4-6-6-4 Challengers to vaunted RS and PA series diesel locomotives. If you have any interest in Alco this book is a must have!

Also consider Mike Schafer's Vintage Diesel Locomotives which looks at virtually all of the classic builders and models from Alco PAs to early EMD Geeps. If you’re interested in classic Alcos, or diesel locomotives in general, this book gives an excellent general history of both. If you're interested in perhaps purchasing either (or both) of these books please visit the links below which will take you to ordering information through Amazon.com, the trusted online shopping network.

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