As long as they have zero subsidy
My guess is that they will extremely expensive and not produce near as much electricity as expected because of the dirt, dust, oil, road kill, etc. that will coat them.
However, I hope I'm wrong and they are freaking awesome and everybody wants to buy them without a single government mandate.
BTW, they need to greatly revise down their amount of roadsurface to account for the fraction covered by trees and traffic. However, even if only 10% of the roads are suitable, that would still be incredible IF, the ever giant if, they are the most cost effective solution. They have advantage of getting value from two sources. One as a superior road and two from the electricity. However, I still think the cost of electricity will be way too high.
Some people say that taxes are the price we pay for civilization. But the runaway taxes of our time are the price we pay for being gullible.