Corrugated railhead is a side effect of running resilient wheels on rigid track. In the early 1950s, the tracks on Market St were done, laying the rail on large concrete pads. By the 1960s and 1970s, the PCCs super resilient wheels had corrugated the rail pretty severely (the Muni stopped running the grinder in the late 1950s). These tracks were ripped out and relayed during the BARTD construction. BATRD itself uses a resilient wheel and rigid track in the subways and elevateds, so these areas are prone to corrugation too. BARTD actually does have a grinding program because in certain areas, the elevateds and subways are quieter than they were a couple of years ago.