The simple cost comparison does not work that way: part of the lower energy output is due to lower peak power per area for the solar roadway. So you can't just multiply the two factors. Still I don't see a chance for getting a competitive price.
Using the roads only makes sense if there is absolutely no alternative other open areas. Using the road is rather expensive and likely short lifetime. A well scratched panel might loose about half the efficiency. Not having the angel for highest energy output could actually be an advantage, as power output is a little less peaked around noon. So the horizontal orientation is not that bad. In Germany they already start using roofs angled to east or west and consider higher payments for them.
There are many alternative places, that are better suited, like roofs and walls of building. A big candidate would be a system that replaces roofing material, not just put on top of a roof. I also think the Korean solution is more realistic if you really need the road area. Especially parking lots are better in the shade in sunny regions.
However I don't think area will get that scare: There is plenty of dessert areas and land, where agriculture is limited by the amount of rain and not by the amount of sunlight. So in dry regions, using something like half the area for solar might even help to make the residual land more useful for agriculture.
In less sunny regions wind power is likely more cost efficient anyway.