Eloise, most likely, was the nickname for the flat car that carried the rails--The track caller, who led the work chants, would give everyone and everything a nickname, to make the job more fun--the names of women were used to keep things interesting, and the work chants were peppered with sexual references,particularly double-entendres- "rock and roll" was an instruction to the work crew, who used the rhythm of the work chant to pull and lift together, but the sexual metaphor was obvious enough, and it was a good way to get a smile and to keep the crew focussed--

Alan Lomax's "The Land Where the Blues Began" has a chapter describing this work, with examples of the chants, and conversation about how they were used. It's a really great book for anyone who is involved in folk music and blues--