A couple more reasons why it's a dumb idea, based on the increasing incidence of regenerative braking systems ....
For the road to capture mechanical energy, it steals energy from the vehicle, reducing the energy available to be recaptured through regeneration. In effect, the driver of the vehicle is paying for the fuel that powers the piezo roadway, rather than benefiting from the regenerative systems on their vehicle.
Then there's maintenance. Public roads are maintained exclusively by public authorities. Private vehicle regenerative systems will be maintained by private individuals. That's one bill public authorities will be happy to avoid (except, perhaps, for their own fleet.)
Regenerative systems turn any down hill and braking situation into an energy recovery exercise. No need to figure out where to place the energy capture system - just keep it with the vehicle.
Also, the energy coupling system is already in place - and in perhaps the most efficient arrangement possible.
I think I've spent more time on this than is warranted. Think I'll step up to something more productive and strip on old washing machine PCB.....