About the speed limit analogy - Highways are often designed for a speed greater than the posted speed, and (in the US at least) the design vehicle is a mid-50s car which manuvers and stops much more poorly than a modern car. This is kind of a problem, as people can sense that their car is capable of safely exceeding the speed limit, and thus they do. The closest thing still made to the "design vehicle" is a dump truck, and lots of small highway agencies post curves based on how much their dump trucks sway when going around them.

I won't say those fellers seem young and stupid, but they make me feel old and wise by comparison.