In Europe, they do this thing where they get rid of curbs and speed signs and have cars and bikes and pedestrians essentially inhabit the same space. The idea is that if there isn't any specific marker delimiting whose space is whose, that cars will slow down, and everyone, because of the uncertainty, will bend over backwards to be polite, and to make sure they don't hurt anyone. It's called Shared Space, and you can find out more about it here. It works.
What you're proposing is similar in concept to that idea. And it may be like going back to the early days of cars, when they weren't built so solidly, and things broke a lot, and people weren't used to sharing the roads with automobiles. People drove more slowly in those days.
Yes, if we had glass cars, people would most likely drive more carefully and take fewer risks. There probably would be fewer accidents, as a result. I don't even know if people would drive faster than, say, twenty miles an hour -- bicycle speed. I bet we wouldn't have to have speed limit signs any more. There would be other benefits, as well. With glass cars, people wouldn't drive fast, and therefore wouldn't want to use them for long distances. It would be too slow. So there'd be a clamor for more public transit. People would live closer to population centers, to minimize travel. They'd probably bike and walk more, and therefore want more village-like situations. We'd use less energy as a result of most of these things, and the price of gasoline would decline.
However, to make this happen, would take federal legislation mandating it, and that would never happen. Not in the United States. Maybe in Europe, although I doubt it. I can see small communities, like Bainbridge Island in Washington State doing this, but not much more. I doubt that many people would see this as an advantage, for it would cut down their independence and ability to live far from population centers. It would also be seen as making cars less safe instead of more safe. Most people like to use technological solutions to problems instead of human behavioral solutions. But I would own and use a glass car if everyone else were doing it, too.
