LIRR mileage WAS calculated from LI City until Penn station opened in 1910. mileage is ALWAYS from L. I. City they are correct, but only as of 1942-43.
Then, mileage was calculated from Penn with the exception of the Montauk branch which, surprisingly enough, was STILL calculated from LI City and the Atlantic branch whose mileage was calculated from Flatbush Ave.
While the LIRR calculated their mileage from LI City, the SSRR calculated theirs from their terminal in Bushwick.
As a result, their route varied slightly from the LIRR’s later Montauk branch , AND, due to many track realignments over the years, their mileage varied from the LIRR’s mileage between the same two points, but only, on average by about ¼ to ½ mile or so. It wasn’t more than ¼ to ½ mile different at that point.
I'm sorry to say that I have absolutely NO idea as to when the mileposts were put in place.
Judging by the differing styles I've seen in photos over the years, they were obviously put in place at different times . . . perhaps to replace a broken or stolen one or perhaps to indicate corrected mileage when track work was done. There were many locations on LI where curves were removed and tracks realigned, thus cutting off distances at varying locations.
As many of those old photos I've seen show nicely manicured markers, the railroad must've sent a crew out every several years or so to paint them back to legibility. Back then, their only enemy was the elements of weather. Today we have vandals added to the mix. Dave Keller, LIRR Historian 12/18/2008,
