David, average height has certainly changed over the last century. I would expect that further change in developed countries will be limited as amongst other factors, multiple generations have now had plentiful food and nutrition. As for cars, now that we are used to for example, a certain level of safety, power operated everything, climate control systems and sound-deadened interiors, would we forgo them in the interests of saving weight? Would you want a tiny car when surrounded by dual cab utes with elevated impact points? It will be a difficult cycle to break. The picture is from the carsized.com website that madmuz mentioned in another thread.