I suggest that we combine infrastructure elements; ie: topping the sound barrier walls that buffer neighborhoods from traffic sounds with solar panels. These walls are supported by metal I-beams footed in concrete.
East-west highways (Interstate 70-80-90) have at least one wall facing south across lanes of traffic. This power could be fed back into the grid through the same infrastructure that is used to power the lighting system.
The value from the energy produced could be used to offset the cost of energy that taxpayers pay for lighted highways. Each panel of the THUNDERBOLT MAGNUM SOLAR system that is sold by the Harbor Freight is aproximately 1'x3' and produces 15 watts @ 12v. My daily commute is flanked by a 3 mile barrier wall (5280' x 3 miles = 15,840 pannels @ 15 watts = 237,600).
Personally, I wish the barrier walls could be constructed of solar panels allowing the capture of more power. The picture I've attached is an example of the solar panels that I have in mind. I am not employed by, nor do I have any connection to Harbor Freight or the manufacturer of the Thunderbolt Magnum Solar panels. I have used this image as an example of equipment that is currently available.