At least in NYC, the "glass" is a plastic laminate over glass, and VERY hard to remove, mostly because in the 1980s (Pre-Rudy) the low lifes used to thing that kicking the glass out of the trains was "fun" - and it took a LOT of trains out of service

As for stuck in tunnel - if there is no fire etc - wait for the crew - what they will do is open the end door (front or rear - whichever is closest to a station), and they bring a small wooden staircase that is just high enough to go from the door down to the track bed - the MTA gets enough people to guide you out, and they do. A flashlight will be a help, as there usually isn't much light

I've seen it done, but never had to do it