All of these have a flaw. Traffic lights, they need to hear when an emergency vehicle comes. My traffic light will hear the siren and all of the lights will turn off except the one that is where the emergency vehicle is coming.Rv's, they have horrible gas mileage. My RV's will be like a Prius or a Insite. They won't run completely off of gas or batteries. The RV's will switch between the two.Semi trucks, they let off a lot of pollution. It will be exactly like my RV.