• Aug 12th 2010 at 2:55PM
  • 32
When the EPA rates a vehicle's fuel efficiency, it doesn't look at the number of seats in the car, it just tests out how many miles it can go on a gallon of fuel. This is a fair way to compare cars, but if we allow ourselves a little bit of mental reconfiguring, we can find an interesting way to compare airline travel with long-distance road trips.

The Wall Street Journal took a look at the relative fuel efficiency of different airlines using the "seat miles per gallon" idea. If we compare the fuel efficiency of various planes divided by the number of seats on those planes, it turns out that flying isn't all that bad compared to driving alone in a car. In fact, the big U.S. airlines averaged about 64 seat mpg in 2009, according to Department of Transportation numbers the WSJ crunched. Of course, your mileage will vary, depending on traffic (air congestion is a killer here), driver/pilot style and the number of people on the plane, but it's still a pretty impressive figure.

Of course, a post like this is just asking for caveats, so here we go: for one thing, the airlines are burning high-octane jet fuel, not standard gasoline. And, of course, using the seat mpg standard, you can double the rating for your car just by grabbing a friend for the trip. Still, a lot of the things that save fuel in your car also work in a plane. Also, plugging in helps with efficiency. As the WSJ writes:
Alaska [Airlines] changed procedures for ground workers so that electrical power is plugged into arriving flights within five or 10 seconds of setting the parking brake, letting pilots shut down engines faster. That and other changes on the ground have saved an estimated 1.8 million gallons of gas a year.
Not bad, huh?

[Source: Wall Street Journal | Image: emrank – C.C. License 2.0]


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  • 32 Comments
      • 5 Years Ago
      You have to consider that while airplanes may (arguably) be less damaging per passenger mile, they allow travellers to cover vast distances in a very short time, thereby opening up journeys that might otherwise have been impossible/not worth the time by car. The danger is that we simply clock up many more miles than we might have had we had access to a car only. Cheap flights have opened up the possibility of holiday homes far away from where we reside, plus they've made international commuting a reality.
      • 5 Years Ago
      What about pollution (g/km of CO2)? Airplanes engines don't have pollution controls like cars, and jet fuel still contains some lead!
        • 5 Years Ago
        NOx is still a problem with jet engines, but due to the type of continuous combustion process, unburned hydrocarbons and soot are almost non-existant, and carbon monoxide is very low. And no, jet fuel does not normally contain lead, unless it was contaminated somehow, as tetraethyl lead was used to improve octane ratings, and jet engined don't need high octane, in fact, jet fuel is much more like diesel or kerosene.
        • 5 Years Ago
        " jet fuel still contains some lead!"

        it absolutely does not.
      • 5 Years Ago
      Compare how you'd like to perish! Falling screaming from 25000 feet or using your ABS brake system!
      Google Activated magazine
      • 5 Years Ago
      i can understand that most people don't know about everything, including perhaps jet fuel, and neither do i; but i don't understand how someone who publishes errant information (like "the airlines burn high octane jet fuel") doesn't bother to learn about their topic; i've been blending transportation fuels for over thirty years and i'm here to tell you there is no such thing as "high octane jet fuel"; and while i am no engine expert, i believe that we currently have two basic types of aircraft engines, reciprocating like our cars, with pistons and valves, etc., that pre-compress the air/fuel mixture for better performance by moving parts up and down, i.e. the pistons inside of the cylinders; these are generally used for smaller craft; and then there are turbines, or jet engines, whose moving parts compress the air/fuel mixture by going around, not up and down; piston-driven engines use the various grades of aviation gasoline, or avgas (which has some similarities to mogas, or motor gasolines that we use in our cars in that higher octane has some benefits - although avgas prefers it's octane from isoparaffins not aromatics); avgas is still allowed to contain some lead anti-knock compound to help prevent the fuel from prematurely igniting under the influence of high pressure and temperature (before the spark plug tells it to at optimum crankshaft position); turbine fuel for jets requires just the opposite characteristics - it does better with compounds that do not resist ignition (paraffins, particularly normal, not iso) and so adding lead, besides being illegal, would only harm performance
      • 5 Years Ago
      Reinforcing my belief that this blog is written by a bunch of Liberal Arts majors, where did you get the idea that jet fuel is "high-octane". Its not. Quite the opposite. Octane rating is a measure of a fuel's resistance to burning. In other words, the higher the octane rating, the higher the required ignition temperature of a fuel-air mixture under the confined conditions in a cylinder. It does not mean that it burns hotter or that it produces more energy or that it's more corrosive or any of the dozens of things I have seen attributed to fuel with a high-octane rating. High octane is required in a spark ignited engine to avoid unwanted detonation prior to the fuel being ignited by the spark or its resulting flame front. In a jet engine, you just want the fuel to burn completely in the limited time it has within the combustion chamber without having to resort to a spark so high octane would be undesireable. The result is that jet engines are much more forgiving of the type of fuel they burn and thus jet fuel is far less exotic than gasoline contrary to the implications of article. Jet fuel is actually a type of kerosene, basically a more refined version of diesel oil.

      In the area of caveats, you might have noted an airliner is traveling at about 600 mph while a car is going about 60. Whether that translates into a shorter trip is another question.
        • 5 Years Ago
        Thank you. I get really irritated by people who act like aviation turbines run on some exotic fuel, and toss around terms like "high octane" to make it sound like they know what they're talking about.

        Jet fuel is little more than kerosene. You know, that stuff you buy for portable heaters, and stinks like diesel fuel?
        • 5 Years Ago
        "Reinforcing my belief that this blog is written by a bunch of Liberal Arts majors, where did you get the idea that jet fuel is "high-octane". Its not."

        Liberal arts majors indeed.
      • 5 Years Ago
      It is pretty funny seeing a bunch of people complaining that an appropriate metric for determining the efficiency of moving people from A to B is wrong because it looks at the actual amount of people moved and challenges their cherished positions. Of course a commuter van packed with commuters is more efficient- that is why we have commuter vans and carpool lanes. Of course an airplane is more efficient even if you assume it is never more than halfway full.

      News flash: air resistance at reasonable speeds < rolling resistance of a tire.
      • 5 Years Ago
      Of course if you take the same measuring stick and apply it to automobiles you will find that full size SUV's get over 150 seat-miles per gallon despite getting less than 20 actual mpg's.

      But, the edge in this case still goes to the airlines as they typically have less empty seats on a percentage basis.....
      • 5 Years Ago
      Throw in a fatality rate that is 62 times lower for plane travel versus car and you definitely persuade me.
      • 5 Years Ago
      We're ignoring a couple of factors that weigh heavily in favor of airplanes: speed and range.

      Speed is a valuable commodity that comes at a price: lower fuel efficiency. Go faster, get less mpg. In general terms, fuel consumption is proportional to the square of the speed. (i.e.--it takes four times the fuel consumption to go twice as fast.) . Since airplanes travel ten times faster than cars, by all rights they should have a fuel consumption a hundred times greater than a car. Yet it's basically in the same ballpark for passenger-mpg. Essentially, planes give us a free 500 mph. This is a testament to the extraordinary efficiency of high-altitude air travel in general (not surprising; no rolling resistance) and turbofan engines in particular.

      The second factor is range. A long-range airliner carries with it enough fuel to travel 8,000 miles non-stop. Imagine if you made a Prius carry that much fuel--400 gallons. Lugging a trailer with more than a ton of fuel would drastically reduce the mpg figure of the Prius, especially in the beginning of the trip. So you'd probably have to carry 800 gallons instead of 400...which cuts mileage even further....etc....etc

      Bottom line: jet airliners achieve a fuel efficiency comparable to cars while traveling ten times faster and 20 times farther. That's a hell of an energy bargain.
      • 5 Years Ago
      Automobile: PRO: you don't have to go through the cancer machine.
        • 5 Years Ago
        Mike: that 'new car smell' that people love is actually the off-gassing of VOCs from adhesives, plastics, paint, and surface treatments. Nothing to do with incoming air.

        You also need specific compounds in your air filter to purify air pollution to any meaningful extent. I'm not sure the average run-of-the-mill automotive filter does a whole lot.
        • 5 Years Ago
        Assuming you use your car at capacity the same way this study assumes airlines fly at capacity:
        Chevy Suburban 18 MPG seats up to 9 = 162 miles/seat-gallon
        Toyota Prius 50 MPG seats up to 5 = 250 miles/seat-gallon
        (see graphic in WSJ article to see what I mean)
        • 5 Years Ago
        No you just suck up all the VOCs in a car's interior instead.
        • 5 Years Ago
        I thought the VOC remark was from following behind diesel cars/trucks.
        When I am on my bike, it is diesel vehicles, or the odd carbureted vehicle that makes me cough/gag.

        What, new airplanes don't have any outgassing materials.?

        My sister purchased a new '10 Sonata (Hyundai was giving super financing), within six months the new car smell was completely gone.
        • 5 Years Ago
        What, you don't have an activated charcoal filter for the incoming air?
      • 5 Years Ago
      And the contrails apparently contribute significantly to global warming. I am pleasantly surprised though by the mileage of planes, it is in the same league as cars. I previously thought it was much much worse. So now maybe I won't feel so guilty about the 5 hour flight I may take next month for the first time in 2 years. I just spent 2 months paddling up the Inside Passage and there were a lot of cruise ships going by and considering the effort I had to put in to maintain 3 knots into the wind and they just plow this behemoth into it at 20 knots and create wake that creates huge waves wherever they go .. I was staggered by the energy they must use. But then again, there are 2000 people on board so on a per capita basis it gets much lower.
      • 5 Years Ago
      Measured this way even the Behemoth Class SUV is great if it's packed full. 15 MPG times 7 occupants is 105 seat MPG.
        • 5 Years Ago
        @JustZitGuy

        Your being as backwards as the original authors.

        You shouldn't take airline industry averages for paying seat miles across all models, routes, etc at the pump versus the best possible efficiencies for other modes of travel.

        A good point is the notation on buses. I have yet to see a fleet of city/suburb buses that size (40+) that actually get 6 mpg in real-world usuage. My city's buses average between 2-3 mpg. Using the Loading Factor/Rough Averages of Sizes, My city's buses really only average around 70 Passenger Miles per Gallon!
        • 5 Years Ago
        There is nothing wrong with calculating passenger-mpg - it is the only way to make a fair comparison across modes. The fact that aircraft load factors are generally 80%, whereas car load factors are typically more like 25%, is what makes the number sound good for aircraft. In actuality 60 passenger-mpg isn't very good.

        Quick figures for you:
        Airline service - typically 60-70 passenger-mpg

        Full Prius - about 50 mpg, carrying 5 passengers (assuming driver counts) -> 250 passenger-mpg

        56 passenger bus - about 6 mpg, carrying 50 passengers -> 300 passenger-mpg

        TGV Duplex service Paris-Lyon with 3 intermediate stops, gasoline energy equivalent of 1.16 mpg, carrying 436 passengers (average load factor is in fact 80%, train has 506 seats) -> 632 passenger-mpg

        And for the extreme high end:
        Siemens Combino light rail vehicle on trial in Basel, Switzerland, gasoline energy equivalent of 13.6 mpg, carrying on average 65 people (crush capacity is 180 people) -> 884 passenger-mpg


        The laws of physics suggest to me that electrically powered rail service is far and away the winner in terms of efficiency, and the real world data bears this out.
        • 5 Years Ago
        FWIW, I am still a fan of aircraft. It's just that I think they should be used for what they're good at, namely really long flights at high speed, especially crossing oceans. There is already a pretty well-established trend in various parts of the world to provide high quality rail service connecting airports. This is a "win-win", as expensive airport capacity is freed up for the bigger, longer flights, rather than being tied up with a lot of commuter aircraft.

        Some corridors that have good high speed rail service essentially have no competing airline service. There's just no point.

        Electric cars tie in with this scheme very well, generally to provide that last to-the-door link on long trips. For those who want to do long road trips, well - I see nothing wrong with continuing to use fossil fuel. Maybe someday EVs will have enough range, and there will be enough quick-charge stations, that fossil fuel for land transport will go away. But I don't see that as something that should be the focus. The main focus should be to get EVs in use ASAP for what they're good at - day-to-day in-city and suburban use.
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