Americans’ penchant for flying outpacing efficiency gains

U.S.-based airlines are getting more fuel-efficient, but Americans are traveling more and erasing potential gains, according to a study out Thursday.

By the numbers: Fuel efficiency of airplanes has increased by 3% between 2016 and 2018, but the miles passengers have traveled increased 10%. Thus, fuel use and carbon dioxide emissions rose by 7%, according to the report by the International Council on Clean Transportation (ICCT), a nonprofit environmental group.

Why it matters: Jet-fueled, commercial airplanes account for just 2% of global carbon dioxide emissions, but ICCT says it is set to triple by 2050 as we — and everything we buy and sell — fly more around the world.

What’s new: Budget airline Frontier took the top spot for the second year in a row as the most fuel-efficient U.S. airline. Two other airlines that are considered similarly affordable — Spirit and Southwest — came in tied for second.

• Those flights are less expensive for the same reason they don't provide a particularly comfortable flying experience: They squeeze a lot of passengers onto their planes, which increases the efficiency.

One level deeper: The chart above shows the relative efficiency of each airline. For context, the least efficient airline (JetBlue) burns 26% more fuel than Frontier.

• Those are averages, which may mask some of the bigger differences between the airlines, according to ICCT aviation and marine director Dan Rutherford. Fuel efficiency varies widely — 20% to 85% difference in carbon intensity — on specific routes depending on several factors, including layovers and aircraft flown.