Fuel efficiency is all the rage in the automotive industry these days, but how has it evolved over the past eight decades? Not very rapidly, according to Michael Sivak and Omer Tsimhoni from the University of Michigan's Transportation Research Institute. New Scientist explains:
[The two researchers] analysed the fuel efficiency of the entire US vehicle fleet of cars, motorcycles, trucks and buses from 1923 to 2006. . . . They found that from 1923 to 1935 fuel efficiency hovered around 14 mpg (5.95 km/l), but then fell gradually to a nadir of only 11.9 mpg (5.08 km/l) in 1973. By 1991, however, the efficiency of the total fleet had risen by 42 per cent on 1973 levels to 16.9 mpg (7.18 km/l), a compound annual rate of 2 per cent. . . . Progress has stalled since then, though, despite growing environmental concerns. From 1991 to 2006 the average efficiency improved by only 1.8 per cent to 17.2 mpg (7.31 km/l).
Sivak and Tsimhoni attribute the rise between 1973 and 1991 to the OPEC oil embargo and the Iranian Revolution. But according to New Scientist, fuel efficiency still only grew a paltry 3.2 mpg overall between 1923 ("the days of the Ford Model T") and 2006. One would think perhaps the rise in oil prices in 2007 and 2008 has fostered additional growth since then, though.