I have an idea on how to make cars stop polluting.  Cars should have a large solar panel on top of them, so whenever you drive the car, it is powered by the sun. when it is cloudy, your car has collected power from the sun. with the power built up, the car can go a week without seeing sun. After a week and there is no sun, you can just plug in your car and charge it.
One other idea I have for cars is to make them self driving, for less accidents. How the self driving cars work, is there is a giant satellite up in space that can detect each car. Each car has a GPS chip in them that coordinates with the satellite  to determine where to go. Since every car is connected to that satellite, the satellite knows where every car is, and can instantly stop, speed up, slow down,  start, etc, no cars will get in crashes any more.