Mile posts can be moved if the line has been freshly surveyed. An example of this is the little shortline I worked for, the Middletown & New Jersey Rwy. It started life as the Middletown, Unionville & Water Gap, and was immediately leased to the Erie in 1869 and received it's first survey after construction and placement of mile posts. In 1872, the New York, Oswego & Midland leased the line, standard gauged it, as well as conducting their own survey (#2) and adjusted the mile markers to reflect a new connection. Not too long afterwards the NY,O&M went bankrupt and turned control of the M.U.&WG over to the New Jersey Midland, which also went bankrupt not too long afterwards.The NJM conducted their own survey(#3) and readjusted the mile markers. During the reorganization of the NJM, it became the Midland Railroad of New Jersey before finally leaving bankruptcy as the New York, Susquehanna and Western. The NYS&W surveyed )(#4) the line and readjusted the mile posts twice(#5). Once, not long after the new company formed, and again in 1908, when they reversed the direction of the mile post numbers (#6). The little RR trundled along this way until 1913, when the ERR controlled NYS&W let the old Water Gap lease lapse, and the Water Gap emerged as the independent Middletown & Unionville, with of course, a new survey and new placement of mile markers (#7). When the M&U was sold in 1946, the new owners conducted their own survey (#8) and erected new mile markers, which are still in place today. Of interest is the placement of MP 1. Due to joint use of the MNJ Middletown yard, defining MP 0 and is a guess at best. The distance from the start of MNJ property to MP 1 is over 6000 ft.! All the other MPs reflect an exact measured mile placement. A lot of money spent on surveying to say the least. The Val Maps of 1916 shown 2 sets of mileposts, the then current ones and an older set. They are about 2 tenths of a mile apart.
