Definfing roles of GP's, RS & F units. : LUSENET : Southern Railway : One Thread

While it's obvious that E units were used for passenger service, F units for freight, it's not so obvious to one with no working rail experience as to what the difference would be as to when the Southern might prefer a GP7 to an RS3 or even an F7.(i.e. how they were each used) Can anyone explain the usage of these typpes of locomotives? (ALso from photos it seems that F units and GP's were used more in tandem than RS2's & RS3's. Is this correct?)

-- Roy Williams (, June 23, 2000


Southern had some dual service versions of the RS2, RS3, GP7, F2, F3, and F7 that were equipped with boilers and signal hoses for passenger service. At one time or another SR used each of these types in regular passenger service. The GP7's and the RS's were generally used on branchline and secondary passenger runs. The boiler-equipped F-units, including the dual-service FP7, were widely used in passenger service. At various times all four of the Southern's streamliners (the Crescent, Southerner, Royal Palm, and Tennessean) regularly used F-units. Southern was big into putting engine sets into regular rotation runs consisting of up to three or four trains, and some might be freights. The F-units fit this bill nicely. Some F's had high speed gearing also. The standard SR diesel gearing was for 65 miles per hour. This can be misleading. This is a rating meaning that a constant speed of 65 will not overheat the traction motors. In reality most engines geared for 65 will run in the low 80's if the wheels are true and the wheel slip systems aren't malfunctioning. The E's and some F's had higher rated gearing.

In freight service, the F's and the GP's tended to mu and perform together better. In later years the Alco's tended to give trouble if you tried to mu too many of them together. In earlier years when their electrical systems were newer and kept up better this might have not been a problem. Generally Southern tried to keep the EMD's and the Alco's in separate sets for through freight service. Even this could present problems. Some Alco and some early F's had manual transition. The engineer had to manually change from series to parallel electrical connections and make shunt changes as the speed increased or decreased. Think of this like a 4-speed manual transmission in your car, only electrical. These engines had to be in the lead or else it had to trail another engine with a 4 position transition lever. The engineer had to make these transition changes even if the engine was not in the lead. Eventually all newer engines had automatic transition. Compatible air brake systems could be a consideration also. Some Alco's had the no. 6 brakestand. In later years SR would only use these together or use them a single yard or local freight engine. The no. 6 brakestand and many of the 24RL brakestands had no pressure maintaining feature once an air application was made. This could be tricky on a long freight.

In yard and local freight service, the Alco's were favored by most engineers, including me. They perforned better in this service. They loaded up faster and were less slippery than the GP7's. At various times the Alco's were primarily maintained out of Columbia, SC, Spencer NC, or Atlanta. The SR tended to keep them closer to their home shops for maintenance ease. I thought that the old Southern did a good job in assigning the right engines to the right train. There were a lot of factors to weigh in, and their practices evolved over time. When push came to shove though, the Southern would move the trains. That is why I saw FP7's in yard service and SD45's on passenger trains in emergencies. The Southern had to move.

Ben Lee, engineer- North Charlotte District

-- Ben Lee (, June 25, 2000.


You really need to get a book out!!! Outstanding answer with insight that is unparallelled!!!

-- Matt Bumgarner (, June 25, 2000.

I agree with Matt, Ben's insight is always the best. I'm sure that he could write a book that any rail enthusiast could not put down. thanks Ben.

-- Roy Williams (, June 25, 2000.

Great answer. We do need more SRR books from acutal members of this RR. Joel

-- Joel Shelton (, November 26, 2000.

Moderation questions? read the FAQ