Dear Pablo,

I recently heard a radio ad by a freight train company, claiming that it moves 1 ton of goods 422 miles on 1 gallon of fuel. Can this be true? And how does it compare to my car’s fuel economy?

The freight company is CSX and its exact claim is, “Trains can move a ton of freight more than 423 miles on a single gallon of fuel.” While this number sounds astounding, and the freight company cites it to show off its “environmental stewardship,” the metric used is quite different than the “miles per gallon” we use with passenger cars.

In reality, it is going to be difficult to make a comparison between a train that carries freight and a personal automobile, which carries passengers (actually it’s usually only one passenger). But let me see if I can make the numbers make sense, and find a transportation lesson in there somewhere.

According to the Environmental Protection Agency, the average car weighs 4,142 pounds, or over 2 tons. The fuel economy standard for passenger cars is 27.5 miles per gallon, set to increase to 31 in 2011. This means that 1 gallon of fuel in your car will move a ton only 13.3 miles, or a fraction of the freight train’s distance.

But as I stated above, this is not a fair comparison, as the purpose of an automobile is to move a passenger. But if we wanted to use the same metric that CSX does — ton miles per gallon — we could come up with a comparison. If we assume the average passenger weighs 190 pounds (the average U.S. male adult weight), or almost 0.1 tons, then we could say that a car actually moves 1 ton by 2.75 miles per gallon.

But again, people are not freight, so let’s look at an 18-wheeler instead. A semi might have a gross weight of 40 tons and get about 7 miles per gallon. This comes out to 280 ton miles per gallon, again using CSX’s metric. Surprisingly this result is comparable to that of the passenger car.