Nothing is free... The spinning of the blades produces drag which pulls on the cars coming on next. You are exchanging a small amount vehicle efficiency for a measly amount of energy. The solar panel may generate some electricity, but its a small panel. Would have been better off putting a roof over the highway with solar panels on.

I saw a similar thing that generated power from a specially designed speed bump. Every car needed to overcome the speed bump, which takes energy...

There are losses in all these transformations as well. I doubt you will ever get out even what is put into manufacturing it.