[2003protege]

This sounds like an idea I would conjure up some random late night my freshman year in college studying engineering, when the world is full of unexplored possibilities and blah blah...

1. this idea probably will be a net loss in time and money.

2. Aerodynamic losses are incurred when you use your vehicle to move air (or heat up air, but that's negligible for cars).

Say the vorteces you leave behind you have an average velocity of Xmph, when your car passes, you've just taken all the stationary air and accelerated it to Xmph.

the logical extreme would be a car that takes all the air it hits to the same speed the vehicle is traveling. So this free air that you're going to slow down via turbines: think of it as using your proposed turbine-generators to accelerate the amount of air they "use" in the direction your car is traveling at a less than 100% efficiency.