Here are some further thoughts on Terry Kenney's project and your comments: It is indeed a good point that the estimates on how many houses this could power is overly generous, to say the least. One thing we don't know, though, is if the 'Dragon Power Station' is only a prototype/proof of concept or if it is close to the best that can be done. This makes a difference. Prototypes are often sub-optimal compromises because you usually need to show that your idea is working before you can get financing and credibility to allow you to do what you really want to do.
Another question without answer at the moment is whether the 'plates' used by this system are softer than asphalt or not. They probably are to extract the maximum amount of energy, but maybe not. If they aren't much softer than asphalt, the system wouldn't extract much more energy from the trucks than the road would on its own (via friction and deformation). It might be the equivalent of hitting one or two potholes (except that potholes don't produce electricity). Still, it's definitely not a free lunch.
But lets assume that the plates are quite a bit softer than asphalt, or that they depress into the road slightly and the truck has to expand energy to climb back up. Maybe the next step is to build a power station at a place where you want to 'steal' energy from traffic. A downhill lane with a stop sign at the bottom where vehicles need to slow down, for example. They'd be hitting the brakes and dissipating the energy as heat anyway, so you might as well turn part of that energy into electricity.
We'll try to track down Mr. Kenney and ask him some further question about his project. If you know where to reach him, please let us know in the comments.