ThinkProgress: A study recently released by the International Council on Clean Transportation (ICCT) found a wide range in fuel efficiency for U.S. airlines. Among the 13 biggest airlines, the least efficient, American, used 25 percent more fuel per passenger mile than Alaskan Airlines, the most efficient way to fly. Alaska, Spirit, Frontier, and Southwest Airlines all so-called budget airlines were the most fuel-efficient airlines for domestic flights in 2014. Other than American, Delta and Virgin America...