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 that model (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 during its two year production run.
Perhaps most notable was the incredible tractive effort it
offered, by far the most of any RS model produced up until that time. Unfortunately, railroads still had yet to embrace
the six-axle concept, 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 at the same time as the RS3. The locomotive featured Alco's standard, but troublesome, 244 model prime
mover allowing for 1,600 horsepower. As with the original
six-axle model (RSD1) the RSD4 was meant to provide a sizable
increase in tractive effort. The model had a slight design flaw as there was
insufficient space for the unit's main generator, which was corrected
with the RSD5 featuring a longer hood and carbody. As a result of this change the RSD5 sold much better than the RSD4 with nearly six times more
units produced during the time Alco cataloged the locomotive, from 1952 through 1956.
One important historical note about the RSD4. From a technical standpoint, the model was the very first C-C design
(meaning all six axles were powered) that Alco offered standard in its catalog.
The RSD1 was merely a specialty order for the US Army and the RSC2 and
RSC3 locomotive were A1A-A1A designs whereby the center axle
was not powered (i.e., lacking traction motors). With the RSD4's six 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. For additional technical information about Alco's RSD4 model please click here.
Production Roster Of Alco RSD4s
Chicago & North Western
Central Railroad Of New Jersey
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 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 increased tractive effort). The five railroads that ultimately did
purchase the model used them as intended, in heavy freight service.
This include the Atchison, Topeka & Santa Fe, Utah
Railway, Central Railroad of New Jersey, Kennecott Copper Corporation, and the
Chicago & North Western. To read more about other Alco Road-Switcher (RS) models please visit the Diesel Locomotives section of the site, which can be reached from the top of this page.