US vehicle efficiency hardly changed since Model T
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 analyzed 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.
The improvements made up to 1991 were in response to two international events — the 1973 oil embargo by the Organisation of Petroleum Exporting Countries (OPEC), and the Iranian Revolution of 1979.