It looks like the insulator manholes needed new covers from time to time. Collect 'em all. In two of the above locations, only one side of the conduit is visible but that's what that rail is. Savor the detail on the corroded iron.
The Broadway streetcar line was built by the Forty-Second Street, Manhattanville and St Nicholas Avenue Railway Company under a franchise granted in 1884. The Broadway line probably opened in 1885, and for most of its existence it ran just about the same route as the M104 bus does today, from First Avenue along 42d Street and Broadway and then 125th Street to the Hudson River. It became part of the Third Avenue Railroad System (TARS) in 1895 and was converted from horse power to electric conduit in about 1898. Thus, the covers all bear the name Third Avenue in some form.