re: #134 b_sharp
The difference is the energy isn’t expended all at once by designing the fence to stretch before breaking. I’m not sure what material they’d have to use, steel probably wouldn’t do it.
Too bad transparent aluminum isn’t real.
The real problem is that cars fragment, and do so in unpredictable ways. If they knew that no piece would ever have a smallest dimension smaller than, say, 2ft across, it’d be a pretty easy problem.