Is There a Way to Encourage People to Turn Off Their Engines?

We know the impact that pollution from cars can have on our respiratory health and even our mental health. Psychologists are trying by testing out road signs with different wording. The first one said, please switch off your engines. You will improve air quality in the area. The next one said, Please join other responsible drive in canterbury. Turn off your engine when the barriers are down. Nd then ther was number three, which said, think about your actions. When the barriers were down, please turn off your engine. So can you tell me why did you pick those three messages, and what was it about them that I thought might work?