Whilst SPG is obviously quite capable of looking after herself in this argument, some support might be useful. I like the simplicity of the opening statement. In a subsequent refinement, SPG is simply stating that the issue is the distance a gallon of fuel will carry four people, regardless of the form of conveyance and is referring to the average fuel consumption of the US auto fleet. In 1908, the fleet was the Model T, so that is a legitimate starting point.
In 100 years, there have been amazing developments in engineering, comfort, safety, speed, acceleration etc etc., but the fact remains that the average fleet fuel consumption still hovers in the region of 25mpg. This is not to say that as reality sets in, more people won't use higher mileage vehicles in future, thus altering the average value favorably. But for today, the statistic seems correct.
The Washington Post article
http://www.washingtonmonthly.com/archiv ... 007007.php
summarizing the CAFE standards for autos and trucks suggests that in 2001 (interpolated from the graph) the target for the combined effect of cars and trucks, assuming a 50% split, is about 25mpg. Could it be that in reality, the actual value in 2006 is lower because of the effect of larger and more powerful SUVs and trucks?
The distance a vehicle will carry a passenger load or a ton of freight on a gallon of fuel is a legitimate statistic and, I fear, one which will become uppermost in people’s mind as time goes by. Of course, the time to perform this is very relevant today, but will become less so. Ultimately, a one hp vehicle may take a whole day to travel 25 miles, but, cheer up, it will use bio degradable fuel!