I think you'll find that you need LESS fan when the vehicle is in motion; which is one major benefit of an electric fan. You're not burning power moving all that air needlessly. Better for gas mileage; which we all know if high on our priority list.
My point is, a garage fan is nothing compared to the vehicle going down the road at 30+mph. In my case, the fan turns off and stays off at freeway speeds; even when climbing a grade. If you slow down below 30mph, it comes on. When you get off the freeway and pull up to the first stop sign, it turns on.