Comment by pge

Vehicles have two primary components of resistance, air drag and rolling resistance. Rolling resistance is a function of weight, and air drag is a function of the frontal surface area (and to a lesser extent the total body surface area). For a small passenger car, rolling resistance is much lower than for a large truck, so they get much greater efficiency gains from reducing air drag. For a large truck, the rolling resistance is so much greater that the gains from reducing air drag are not large. That's why big tractor trailers don't have the same optimized aerodynamics that a tesla or a prius has.