Right down to the central driving position and absense of external mirrors.
Second thought: the transition from the top of the windshield to the roof seems too sharp (even Rumpler's car appears to have a more generous curve at that point). The fact that engine cooling is exhausted through the roof is interesting, but even considering that would help to raise pressure behind the transition, it's a little hard to believe the sharp angle wouldn't generate a lot of turbulence. Would be interesting to see a smoke or tuft test to visualize airflow up there.
A similar test would be interesting at the lower part of the windshield to see the effect on flow of those cooling inlets at its base.
Other stuff: nice tight front wheel arch to tire gaps; smooth & flush bodywork from the front to rear wheels is good; the wheels themselves could be cleaner - the diagram appears to show a dish shape. Why not go smooth?
the shape might be intended to deflect more air sideways than over the truck.
the sides of a truck+trailer would easyly make out two to thee times more the aerodynamic surface than the top of the trailer so yo might want to keep the flow attached as much as possible there. the front roofline looks as though it might defect the air upward and since most trailers are higher than the truck this migh work in combination with the standard roof fairing in front of the trailer.
i'd like to see this design on the road, as it offers much better sideway visibility. many cyclists die every year because they're in a blind spot of trucks making a right turn.
Yep deflecting the air to the sides gives twice the amount of room for the air to get out of the way as going over the top. Simple curved windshield works best optically and is the next best shape to a sphere. It also forces air downwards away from the top and reduces glare - ever have a flat windshield blind you from the sun reflection?