I thought the point of solar roads wasn't that they were more efficient than, "just putting them on buildings or the sides of roads" it was more of a way to utilize otherwise "wasted space". As in, when you're laying down a new road why not add some solar generating capacity as just another thing you lay into the pavement just like those little reflectors or paint.
Because it's cheaper and easier to maintain to put the solar generating capacity next to the road instead of "on the road". You get twice as much solar capacity when you put it beside the road for the same money (installation + maintainance) -> better.
