A Southern Georgia school district is considering ordering 53 propane-fueled school buses. "They're healthier, they're cleaner burning, and they're much quieter than the diesel option," said a school administrator. Propane-powered buses also reduce greenhouse gasses by 22% compared to gasoline powered buses and 6% compared to diesel ones. But they come at a premium-$103,000 for a propane model, $15,000 more than the diesel equivalent. The propane bus operating cost (above and beyond fuel cost) is 30 cents/mile, compared to 40 cents for the diesel. Diesel fuel costs about $2/gallon in Georgia, about $1 more than propane.

Bus mileage is 12 mpg for the propane model vs. 10 mpg for diesel. The life of a school bus in the district averages 9 years, and each bus travels an average of 30,000 miles per year because the district is so large and rural. Which bus is the better choice based on a life-cycle analysis?