is this the equivalent of a leading edge flap on a wingprofile?
To me it looks like the front corner treatment of trucks:
I asked this question in 2006 when Honda and other teams had those large sidepod winglets.
Since then I asked a former automotive aerodynamicist (my old lecturer!) and he said one of the reason's is to keep the truck's clean. They capture a lot of dirt and dust from the engine, road, other trucks. Keeps the cab steps clean too, and of course for image purposes for haulage companies.
edit - However, he did say they more than likely provided some other aero effect.