Tracks that run 1m70y will generally have small poles 40 yards inside the 13/16m, 9/16m, 5/16m and 1/16m poles; otherwise they will have discreet painted lines, usually red, on the top of the rail.
And the reason 1m40y and 1m70y exist is because going all the way from 6f to 1/16m is too wide a gap, and these tracks have too short a run to the turn and/or too tight turns to run two-turn mile races.
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