content: That would only be worthwhile if the roadway maintenance costs proved to be higher than building them as a car port. The thermal aspect (heat island) would be the same regardless since no car is going to spend enough time on the road (pending heavy traffic) to actually absorb more sunlight than the road. The road reflectivity would be the same as the car port version for calculation purposes. Personally I would adopt the carport methodology, but apply it to parking lots since those will hold more heat than the roadways from the simple fact of having a greater surface area, plus with the carport you can significantly reduce your pollution load from stormwater runoff by keeping those parking lots free of water. Shading the cars when parked would be a nice added benefit.