— Gordon Osmundson, Oakland, Calif.
A According to the Historical Thesaurus of the Oxford English Dictionary, this is an American expression, first noted in 1903 and denoting a temporary track.
The word “shoo” means go away, and presumably to do so “on the fly” is what the track is meant to achieve. The word shoo-fly has other meanings, too, including the well-known pie (in which the molasses is expected to attract flies), a policeman, and the most relevant, I suspect, is a child’s rocking horse (or other animal), dating from 1860 according to Merriam Webster. If you consider that such a chair rocks from side to side, perhaps that can be seen as inspiring the thought of a track being taken to one side. William Mason Camp uses the expression shoo-fly track in his wonderful 1903 book, “Notes on Track,” and so perhaps he coined it, if the date in the Oxford English Dictionary is accurate.
— Andrew Dow
