In order to be more energy efficient, I will use less gasoline by carpooling, making fewer trips, and eliminating unnecessary travel. According to the InterAcademy Council, the transportation sector accounts for 22 percent of global energy use and 27 percent of global carbon emissions. About 2/3 of this is from road traffic. Unfortunately, most vehicles on the road only have one passenger! By carpooling with just one other person, you can cut your road traffic carbon emissions in half! As well as pay less for parking and petrol each month, get to work faster by using high occupancy lanes, and even make new friends! To calculate how much CO2 your car emits, you can use this handy form. If you don't live in the UK, you can just ignore the part about taxation, and just look at the CO2 g/km. http://www.whatprice.co.uk/car/carbon-emissions.html