Glass is much much harder than asphalt. Glass may be poor for being too brittle, or not bendable enough or too hard but not for being too soft.
(Ashalt 1-2 on Mohs scale
Glass 4.5-6.5 on Mohs scale
Mohs scale may not be ideal but glass is clearly and obviously harder so why are you saying it is too soft?
I'm sorry. I should have been clearer. Asphalt is the official name for the bitumen that exit the lowest stage of a distillation column. And you are right that is a very soft material.
However, when I talked about asphalt I meant what is officially called "asphalt concrete". That is the stuff that we use as top layer for roads around the world. It's a composite material, consisting mainly (95%) of rocks, gravel and sand, and only 5% bitumen, which holds everything together.
Asphalt concrete is harder than glass, since rocks and sand are harder than glass, as you can see in this video, at 14:15 minutes :
The bottomline is that a glass road will wear out faster than asphalt concrete, but even worse : it will scratch very easily which make it opaque and thus unsuitable as a cover for these solar cells under it. So normal wear and tear will quickly destroy the one advantage (translucency) that glass has over asphalt concrete.
Asphalt ideal? Don't potholes indicate it is too soft?
A road surface is subject to immense torture over its lifetime, so any material will eventually crack, break or wear out. For asphalt concrete that is some 5-10 years. Reinforced concrete is stronger (and a lot more expensive), and will last longer (10-20 year) but even that will start to crack and chip and break eventually. A road made of glass will certainly not last that long, with the additional disadvantage that pieces of glass all over the road, and glass dust blowing in the wind would cause additional safety and health issues.
The reason that I think asphalt concrete is (close to) ideal as road cover is not just that it's low cost and durable, easy to repair (with bitumen) and its superior braking properties, and limited glare issues, etc but also what you can do at the end of it's life :
A worn out asphalt road can easily be scraped up, heated, add some bitumen, and put it right back down as a brand new road. In fact, 99% of asphalt concrete gets recycled in that way.
Try to do that with a glass road (not even considering one with solar panels under it).