Have you ever been in a vehicle that was involved in a bad accident?I don't think an average sized adult can fit through the read windows. Using it on the front windows is pointless for the passanger in the rear if the driver is incapacitated.
It's amazing what adrenalin will make a person do; they've shown that in a plane that has to be evacuated, that people will slide themselves across the tops of the seats just to get out; they will do what it takes to get out.