It would make far more sense to place the panels above the road rather than under it. Above the road, they would be far cheaper to install, are out of the shade and can be angled towards the sun so far more efficient, keep cars underneath cool, keep the road surface dry and snow free and hence make the road last longer, are easier to maintain and replace without affecting road users, and can still be connected to lights embedded in the road surface or above the road.

The ideal location for solar panels is above car parks in warmer climates (southern states of the USA, southern Europe, Australia, South East Asia, Middle East) like in this image:

http://www.ereleases.com/pic/EEProCarport.jpg