It's just siphoning energy from the air after it's interacted with the car.

Correct me if I'm wrong, but it also interacts before it passes, and while its passing as well. As the car approaches the vicinity of the turbine, it has to push the air in front of the car out of the way. (When a car drives by you, you can feel the current in the direction the car is moving and some to the side). If there are obstacles perpendicular to the current, then the current is impeded more than if they were parallel, creating more resistance.

Like, if you were to flood a street with tennis balls that had tiny perpendicular walls along the side of the road. They would still flow down the road, but the walls would impede their movement along the sides, slowing the total rate at which the balls could move. Instead of just flowing down the road, they would slow down and bump into one another along the sides. Like the rocks in whitewater rafting.