It’s certainly not unique to NJ: it happens on a lot of older trains in Europe, but I’ve never seen it so bad as in the NJ photos.
I guess something about the coating they use on the glass (to improve safety, insulation, etc) makes it vulnerable to clouding and scratching over time. Climate, air pollution, and/or cleaning techniques used over the years may have contributed to the issue?
"Metro-North Railroad and NJ Transit use a single pane of polycarbonate glazing almost a half inch thick, according to the Federal Railroad Administration.
"NJ Transit isn’t alone in this problem.
"“The south side of the (Long Island Rail Road) M-7 fleet of 830 cars is also opaque,” Versaggi said."
LIRR trains run predominately east-west routes, and (I assume from this comment) apparently do not turn round at the termini.
It does not quite say that the affected LIRR trains also use polycarbonate windows, but it seems likely that they do, and that the cause of the opacity is sunlight damage to polycarbonate, or some plasticizer or other minor component of the windows. It is well-known that polycarbonates absorbs UV, and that energy has to go somewhere...
(Believe the statistics or not, comparing the antique, hardly used, minuscule network of the USA to the state of the art, enormous, and insanely heavily utilized Chinese railways is pretty hilarious hubris for Americans, and I’m speaking as one—who left the country, though)
https://pedestrianobservations.com/2011/06/02/comparative-ra...