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Pole lines originally carried communication lines: first telegraph, then telephone. With the advent of automatic block signaling, they carried power to charge the batteries that actually ran the signaling system, or a.c. power, but in some cases the signals remained battery powered, particularly in remote areas with no readily available commercial power. With the advent of absolute permissive block, the pole line had to also carry a pair of wires for the signals to communicate with each other. With the advent of Centralized Traffic Control, the pole line had to at first carry individual circuits (very wire intensive) and later with the development of "coded" signals, they had to carry the code wires. One by one, these functions were removed. Communication went to microwave or commercial Bell lines. Code lines went to through-the-rail systems. Power has been about the last remaining function, and it's primarily gone to commercial drops. In remote areas, solar panels are sometimes used, but because they have to charge batteries -- and batteries are a big maintenance item -- commercial power is by far the more popular choice, even if lines have to be run a long way. As each function came off, so did the wires that carried them -- partially to prevent them from shorting out the still-active lines if and when they broke, partially because they have a positive cash value for the scrap copper, and partially to simplify maintenance of the remaining lines. In general, railroads are deleting all pole lines wherever possible, not because the land they occupy is valuable (it isn't, except for track), but because they're a big maintenance expenditure and are unreliable. I'm not aware of any railroad using any of the fiber optic lines along their rights of way except by happenstance because they buy phone service just like anyone else. They are not using them for signaling circuits per se to my knowledge -- at least, I am seeing no evidence that there is any intertie at all. Railroads did often lease lines or crossarm space to Western Union. I'm not aware they ever leased any to a Bell company. In general, new signals and deleting pole lines ARE tightly related. New signals are almost always through-the-rail coding.
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