Back in the late 80s when I was a kid, I took Amtrak with my parents and brother to Grand Central Station in New York City.  The loading area and corridors were lit with open 2-lamp F72T8 fixtures with 38W Sylvania lamps.  This was long before the modern T8 electronic ballast era, these were the old 200mA lamp type.  None of the lamps were black end EOL, but at least one was dim and purple at one end (mercury migration, but I didn't know what that was at the time).  I always suspected these were powered with resistor ballasts directly from the 600VDC track circuits (Amtrak's locomotives run on a third rail through the tunnels into NYC).  There were also a few two-lamp F42T6 or F64T6 fixtures (can't remember which, hey, it was 27 years ago!), the only ones I've ever seen outside a display case.  Does anyone here know about these unusual fixtures in NYC?  No idea if they're still in service.  Anybody know about fluorescents powered from a track circuit in general?   

In rail cars, the lighting is mostly operated from the onboard battery, usually something between 24..48V.
To run the fluorescents, electronic ballasts for these are in use since early 70's (since the first power transistors were made reliable enough), mostly (pre-2000) as flyback oscillators, so bery frequently feeding the lamps by just one pulse direction, soi by DC with all the consequences. The reason is, the flyback gives quite an asymetrical voltage, so even when the DC of that voltage is zero (it is a transformer secondary after all), the non-linear nature of the fluorescent make it to rectify, so the current become just pulsed DC.
Some ballast fight the rectification by auxiliary heating the second electrode (making the lamp more linear), but once the heating circuit fails (bad contact,...) or the cathode get worn out, the tube starts to rectify again.