Society has much more to gain from improving a car from 15 to 16 mpg (6.38 to 6.8 km/l) than from improving a car from 40 to 41 mpg (17 to 17.43 km/l)," they write in their paper. "Similarly, the benefits are greater from improving a truck from 4 to 4.5 mpg (1.7 to 1.92 km/l) than from improving a truck from 7 to 7.5 mpg (3.19 km/l)."
SHOOT: We need to get smart now.
The average fuel efficiency of the US vehicle fleet has risen by just 3 miles per gallon since the days of the Ford Model T, and has barely shifted at all since 1991.
Those are the conclusions reached by Michael Sivak and Omer Tsimhoni at the University of Michigan Transportation Research Institute in Ann Arbor. They 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.
Electric vehicle research continues to advance and now has high-profile governmental backing, but it's unlikely to have a short-term impact on average fuel efficiency in the US.
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