Originally Posted by wphamilton

Apparently they are designed for both scenarios.



Laminar air flow tests are very useful for low speed air flows. This is an important point, one which I believe another poster has overlooked when he opined that only the frontal area should matter for aerodynamics.



Well they are comparable I think, although at extremely high Reynolds numbers (high speed) flows are more turbulent.



I think that you're postulating a ubiquitous turbulent condition at ground level along the roads. I'd agree that wind tunnels do not simulate that kind of environment - but IS there really such a phenomenon? I'd expect something like the normal pressure gradient and associated flows resulting from surface adhesion.