Be yourself; Everyone else is already taken.— Oscar Wilde.
This project is an excellent example of spending tax money on ridiculous things. While every single engineer who has a piece of paper and a pen predicted the efficiency of Solar Highway, the eurocrats continued to spend taxpayer money zealously.
If compared to commercial solar panel installation, which gets a regular cleaning, maintenance and has the solar panel efficiently oriented to the Sun, the solar roadway will never ever achieve the same efficiency! Because it always looks at the Sun with the same, not optimal angle and is regularly shadowed by passing cars!
Another stupid idea is to put technology in attempts to make the solar road able to resist the damage. The road construction industry spent ages in cost efficiency optimization. Replacing the road coat with costly solar panels will ruin the ROI for both: the road and solar energy projects.
I doubt that such solar roads will be a part of the nearest future. No matter how much money will be spent on research and how many coffees the engineers will drink.