MUed Diesel Locomotives

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One of the many reasons why diesel locomotives beat out steam locomotives was that you could increase the horsepower available to pull a train by adding more locomotives to the train without having to add more crew members. Connecting the controls of the locomotives so that they were all controlled by the engineer in the lead unit allowed Multiple Unit power. Likewise, if a train was short, you could remove units and use them on other trains.

While taking pictures of the depot in Murfreesboro, TN, I noticed that there were three CSX engines parked along a public road, 2018, 2305, and 6942. I've been up close and personal with single units at museums and industries such as the CGB grain elevator in Only, IL. But the only time I have been close to MUed units was standing on a commuter platform as a freight train goes past. I've seen them from a distance in railroad yards, but I would have to trespass to get close to them. But here I could legally get close to multiple units that were standing still.

I took shots of each locomotive because they were all conventional cab (narrow front hood) units, which means they are older units. But the paint looks new. So I knew they must have an interesting history.

When I took the third picture, all of those MU cables caught my eye; so I took advantage of my close proximity to stationary units and took a close up.

When I got home, I used The Diesel Shop to research the locomotives. Unit 2018 is a GP38-3. It is part of an upgrade program during 2014 and 2015 to rebuild old GP38/GP38-2s to GP38-3s. It probably got a new prime mover (engine), new AC generator and motors, new control electronics, and new paint. Unit 2305 is a slug that was rebuilt from a GP35. It was originally C&O 3527, which was built May, 1964. I was surprised it was a slug since it still has a cab. But leaving the cab on might have simplified (i.e. cheapened) the rebuild. And it makes the mother/slug bidirectional, which would simplify operations. So instead of installing a new prime mover during the rebuild of 2305, they just added weights to it. Unit 6942 is the slug's mother, a GP40-2. So these cables are between a mother and its slug. That would explain why there are so many cables. In addition to the usual air brake lines and control cables, there are cables to deliver the power from the prime mover in the mother to the traction motors in the slug.

I zoomed in on the front of 2305 to get the connections with 2018. This would be the normal complement of MU connections.

Slugs are designed for low-speed operations where a lot of tractive effort is needed, but not much horsepower because of the low speeds. Typical applications are pushing cuts of cars over a hump or transfer trains between railroads on a belt-line route in a major metro area. I assume that CSX currently has a glut of power and that these units are being stored on this weedy siding. The derail on this siding that I documented near the end of the depot posting is more evidence that these units are in storage. One doesn't normally see such freshly painted units being unused.