Solar FREAKIN roadways is a nice idea, but then again is a pogostick that can hop to the moon as a cheap, reusable trans-orbital vehicle.
Is it plausible though. Well it basically proposes the union of 3 or 4 technologies. LED lights, solar panels, and glass roads.
Glass really isn't a feasible material to make roads out of.
1) its too expensive. Just coating the US road system with roads would cost many times the federal budget.
2) Its too soft. Even with a textured surface for traction, it will wear away too quickly. Dirt on roads is basically small rocks, which are generally much harder than glass. Imagine taking a handful of dirt and rubbing it a window. Now imagine doing that with the wheels of a 20 ton tractor/trailer.
3) I have doubts about the physical properties of the glass to take the load and mechanical heat stress required of a road making material.
Solar panels under the road is a bad idea from the start. If they are under the roads, they are hard to maintain. They will have reduced light from parked cars etc. They are fragile. Not really congenial to the conditions you are likely to get on a road. In many ways building a shed over the road, or just having solar panels by the side of the road is a far better idea. However the power transport really isnt practical. One of the most efficient ways to transport electricity around is as high voltage AC. However to build those lines would probably double the cost of any construction. To bury the cables is even more expensive.
LEDs for variable road marking have been partially implemented. They are usually only cost effective in dynamic traffic management systems. For most roads its utterly pointless as the road markings almost never need to be altered. These LED are usually not easy to see (especially in full daylight when the solar panels are meant to be generating power).
However solar powered roadways has generated well over a million dollars for Julie and Scott Brusaw (a therapist and an engineer).
I'm still on the fence as to if they are just delusional dreamers or (now millionaire) con artists. A lot of this looks like just direct 'what if' daydreaming, but then you get the part of the promotional video where they are shoveling ground up coloured glass into a wheelbarrow, while narrating that they use as many recycled materials as possible in this project. It's very difficult to not see that as a direct lie. They must know full well that they did not use any of that material in the construction of their glass tiles.