"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...