I found out a while ago that buses tend to get less than 10 miles per gallon. Initially, that seemed appalling. But I then got to thinking about the number of passengers, and figured that, in terms of efficiency and environmental impact, you should really multiply the number of passengers by the fuel efficiency. My car gets about 20MPG, but if I carpool with someone who also got 20MPG when they drove, in a strange way, we’re at 40MPG. It turns out that the term for this is “passenger miles per gallon.”
So then I wondered how different modes of transportation compared. I happened across one of Wikipedia’s many strange articles, Fuel efficiency in transportation, which told me much, much more than I wanted to know about the matter. It’s hampered by the fact that it uses many different units of measure interchangeably. (Megajoules per kilometer?!)
A bus is stated as getting 200-300 “passenger miles per gallon,” which seems pretty respectable.
CSX advertises that their trains move a ton of freight 426 (?) miles on a gallon of fuel. It turns out that this isn’t even a good number, it’s just the industry standard. A casual observer might not notice the “ton of freight” qualifier, though. The Association of American Railroads claims an industry average of 457 ton-miles per gallon, which is the unit CSX is using. (Actually, based on that, CSX is below industry average?) Strictly in terms of “distance on one mile of fuel,” trains seem to get 1-2MPG on average. A fully-loaded train, though, can carry hundreds of passengers; a Colorado rail line is stated as getting close to 500 passenger-miles per gallon.
Airplanes seem to need several gallons of fuel per mile, implying less than one mile per gallon. But multiply by the number of passengers and you can get close to 100 passenger miles per gallon. (For a full jet. A private jet carrying a handful of passengers is much lower.)
How about boats? I’ve read about bunker fuel used on ships, which is apparently literally the bottom of the barrel, a sort of sludge that needs to be heated before it’s even a liquid, and its absurdly bad environmental impact. But maybe boats are efficient?
My goodness, no. The Wikipedia article only cites the Queen Mary 2, which is perhaps not a representative sampel. But it uses one gallon of fuel to move 41.2 feet, implying about .008 MPG. (?!) It can hold 1,777 people, for 13.9 passenger-miles per gallon. That’s still appalling.