Cool concept, but damn that thing must be REALLY hard if it's not gonna crumble under heavy vehicles.
And yes, it would be way too expensive. Even now, solar panels aren't everywhere as they're still pretty expensive. To totally reconfigure roads into this would take thousands of years tbh.
This needs to happen. Long term benefits are insane. Unfortunately, the big oil firms will do everything possible to stop it and too many politicians are stakeholders in such firms.
They reached their goal so I hope this develops into a real possibility.
It will never happen if people don't take risks and accept that change is needed or make up excuses. I sincerely hope people are brave enough to stand up with these engineers and demand the risk and the change.
Hopefully I see it before I turn senile… 
