Green your driving routine. In doing so, you'll keep more cash in your wallet while curbing your carbon emissions. The first step is to try relaxing while you drive. That's because speeding, accelerating or breaking excessively can reduce your gas mileage by as much as 33%. Obeying the speed limit is another great way to save on gas. According to the EPA, every five miles per hour you drive over 60 mph costs you an extra 30 cents per gallon. Finally, remember to turn off the engine when you're parked. After all, you get a whopping zero miles per gallon when you're idling. Shift your driving habits into a new gear today.