This interests me quite a bit, there was once an LIRR line that went from Mineola to West Hempstead. The ROW through Garden City is easily visible, although I have not found any tracks, unusual looking power lines travel throughout the right of way all the way to the Mineola substation. These do not appear to be for LIPA commercial 3 phase power but for the RR, either for signals or third rail. They stretch all the way down to West Hempstead.
You can see them on Streetview here http://goo.gl/maps/MZBPr in Garden City and further south (poles on the right) http://goo.gl/maps/KKxOu .
Also an image of them in Garden City between Franklin & County Seat.
