".... slowing down can really save money and carbon. Each 5 mph you drive over 60 mph saves about 7 minutes on a 100-mile trip, but costs the equivalent of paying an extra 25 cents per gallon for gas. You’ll also emit an extra 1.5 lbs of CO2 every 20 miles. For the average American, the difference between driving at 75 mph and 65 mph — or 70 mph and 60 mph — adds up to almost $300 and 1,400 lbs of CO2 each year."
"Different vehicles achieve maximum fuel economy at different speeds, but on average mileage increases until 25-30 mph, stays about constant until 55-60 mph, and then declines rapidly. Why? At that speed air resistance starts to overcome even the most streamlined design, because the power required to overcome the force of air resistance is proportional to the cube of velocity."
Each of us can reduce our carbon footprint by just slowing down, even if we are driving a high efficiency vehicle. Air resistance hurts the most aerodynamic vehicles. And anyone can do this with no additional investment!
I'm not sure I believe in global warming, but I drive 55 mph (the speed limit for big rigs and towed vehicles in CA), because if it is true, to do otherwise would be irresponsible.