I was remarking realier how, um, drab, a gp40 and slug were looking. Makes me wonder though if there is a particular operational reason CSX would call for a slug on the River Line. ...or no reason other the slug and its mate were next on the ready line when they needed to hook power to this train?
Well, aside from the reason that has already been provided (that they were next in line), possible reasons include:
The "mother / slug unit" were a better choice for use than 2 diesel locomotives, where extra tractive effort was needed to handle switching duties along the route; or
The "mother / slug unit" were being ferried to an intended destination point via one or more train assignments; or
An available locomotive shortage required the "mother / slug unit" be used to meet train assignment needs.
ACLfan