I finally found a picture of a gandy dancer. Not the two
horizontal bars. Two men on each handle, pushing alternately up and down propelled it, and looked as though
they were dancing, at least enough to give rise to the
somewhat humorous name.
http://www.trainweb.org/screamingeagle/gallery/stuhr/gndydncr.jpg

wwh, MW gives a different definition:

Etymology: perhaps from the now defunct Gandy Manufacturing Company, Chicago, Illinois, which made tools used by railroad laborers
1 : a laborer in a railroad section gang
2 : an itinerant or seasonal laborer