Here is the thing. Even if they could get these things to deal with even moderate traffic, why would you put something as fragile as a photovoltaic cell in such an extreme wear environment when a much more hospitable environment often exists only a few feet away? A single row of solar panels along that road in France would have produced the electricity they needed at a fraction of the cost and would still be working today.That road was installed 3 years ago and was the first attempt. In that time, the tech has changed quite a bit, and several companies are investing and developing solar roads. I could see it being viable enough in the next decade to be used commercially. Especially in Florida on a parking lot that has no semi trucks driving at highway speeds and few leaves.
December 17, 1903, Orville Wright piloted the first powered airplane 20 feet above a wind-swept beach in North Carolina. The flight lasted 12 seconds and covered 120 feet. Tony Jannus conducted the United States' first scheduled commercial airline flight on 1 January 1914. The 23-minute flight traveled between St. Petersburg, Florida and Tampa, Florida...... Things can change really fast.
Even if we look past the durability factor, you need a transparent surface covering them. The cost in regularly cleaning the rubber left behind by car tires would be insane. It also does not help when you regularly cover a fair percentage of your solar cells with cars. If you have ever researched solar panels you will know that partial shading really kills the efficiency of a solar panel.
Solar roads are just a bad idea pure and simple. It is like one of those tools you see on late-night TV that combines two tools together and then fails to work as either. If you want to make roads generate electricity, piezoelectric or even the hydraulic driven generators used in wave generators are much better options that sidestep nearly all of the solar road problems.