road-worthy airplanes have their uses -- for people who have to travel to a lot of remote locations (say, if you own/maintain several radio transmitters spread throughout the rural parts of Kansas, you can cut down significantly on travel time by flying from local airfield to local airfield and then driving to the tower.) They're not a mass-market technology; they're a specialized product for people with very specific travel needs.

Solar roadways, though? I don't see any need that actually meets.