While i hate to get off topic, here's a few things Thunderf00t pointed out: 1) How do you get traction on glass in bad weather? How is a 20 ton tractor trailer going to even stop on glass? 2) Even dirt will erode the glass if there's cars on it. 3) You can't see LED's outside during the day. Especially at and angle and 20 feet away in your car. 4) Putting solar roadways in place of parking lots wouldn't be worth it, considering cars park on it during the day. A solar roof over the parking lot would be much better and totally feasible. 5) It's damn expensive. 6) If you don't quickly move the energy, (Preferably at high voltages), use or store it, you lose part of it. And these are just a handful of problems he pointed out.