The should do the simple tests first.
They claim that the glass cover panels can hold up to traffic and provide sufficient traction. Why not mount just the glass covers over a stretch of road and see how it behaves? Until they get the covers right, the rest is irrelevant.
Once they have the ability to make a glass roadway, then they can deal with the question of what to put under it. How about just LEDs for traffic marking? Will they work in the day time? Will they put out too much light pollution?
Once they have the traffic markings working, they can get the heating elements needed for installing where it might snow. I'm under the impression that they have to melt the snow because the panels won't stand up to snow plows. Maybe it will make more sense to run pipes with heated antifreeze solution instead of direct electric heat. Maybe it will make more sense to redesign the glass covers to stand up to snow plows.
Once those are solved, putting in solar panels is a no-brainer that helps the economics of the project work.
In the end, once all the technical issues are solved, it's a matter of economics. What is the cost of a road made with the panels over 50 years as opposed to a traditional asphalt or concrete road when all the maintenance is factored in for each road type?
Considering all the above, I'm convinced that it makes much more sense to put solar on rooftops.