Dave's argument starts with real-world numbers regarding solar insolation and PV conversion efficiency to establish a baseline. The exact details of a specific implementation won't change the broad conclusion that the energy balance alone, even if you take out the gee-whiz features of the Solar Freakin' Roadways design such as LEDs and networking, doesn't make sense.
When you add all the other stuff on top, it only gets worse.
Fundamental issues: Only so much sun hits the earth, and PV cells only convert a certain fraction to usable energy. When you mount them flat on the ground, you reduce their efficiency further because they're not perpendicular to the incoming light. When you put them under thick enough glass to support real physical loads such as cars and trucks, you lose even more. And when you distribute them over a large area, transmission losses become a Big Deal.
I'm personally skeptical you could build solar panels that would withstand actual vehicle traffic, at least the way we build roads here in the US. Real world roads aren't flat, and they change shape over time as they wear and as the road bed settles and degrades. But real world glass isn't very plastic, and won't conform to a changing surface. It's more likely to crack and break into many pieces. Likewise for the PV cells under it. You'd have to put some beefy steel plates under these to guarantee a sufficiently flat mounting surface to support the load-bearing glass.