If you want to be "green" buy a small hybrid car. They are the cleanest and most friendly to the environment but typically aren't the best value. A small fuel efficient vehicle is the best choice for most people due to the cost. Also you'll find gas vehicles could get significantly better gas mileage if it wasn't for emission standards. Lowering certain emissions (NOx) comes at a cost to fuel efficiency. Also lowering speed limits could reduce emissions but yeah nobody gives a shit about that ugh