Yeah but... why roads? Why build solar roads specifically? Nobody is arguing against solar power. What benefit do solar roads provide that solar roofs don't? Because the roads will ALWAYS provide less power per square foot no matter what technology advancements happen.
The key benefit of solar roads is the reduction in toxic, non-reusable materials. Glass is just easier to get, form, and re-use than asphalt, which simply is toxic waste, temporarily held in semi-stasis in the form of a road. In the pacific islands they use shells for roads. Hard on the tires, but almost infinitely reusable for them. In India, they have thousands of miles of road made from recycled plastic waste. It's an improvement, but - over time - the road is just a temporary placeholder before the plastic makes it to its final home: unreducible waste.
If you are claiming glass is a better top surface than asphalt construction, you have a ways to go to show it. I couldn't find anything on shells in roads, but unless you are talking about something equivalent to a compacted gravel semi-improved road, I bet they use a binder, and I bet the binder is asphalt. Easier to form seems unlikely since asphalt melts a lot lower, and to render glass to give it some impact resistance requires tight temperate control. So you can't feed sand, lime, and soda into a paver and spit a tempered glass road surface out the back. If you want tempered, you make it in a plant and buy a brick paving machine if you don't want to lay your cobblestones by hand. You can feed asphalt and aggregate into and roll a lane's width of road that hardly needs more than striping. And re-use: when they resurface asphalt, the asphalt binding and the aggregate are reused. And another thing is pedestrian hazard - asphalt is petroleum, but at least it sticks to the aggregate mostly. Glass chips won't and thats a hazard, and if they grind small enough to blow around and breathe they're a worse hazard. And there is a trade-off between hardness and flexibility that goes into road surfaces- too flexible and the surface cracks, to stiff and any settling causes it to crack. Asphalt doesn't have some great combination of properties that makes everyone used it, it just wins out because it's easy enough to build and forgiving enough to roadbed prep and cheap enough (because you're using the same material over and over) and predictable and time tested enough. Glass as a road surface has a long uphill battle to fight.Glass is just easier to get, form, and re-use than asphalt