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.
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.
"By the mid-90s there was only us and the Sierra Club [a US grassroots environmental organisation] pressing for better standards," DeCicco says. If manufacturers addressed energy concerns at all, it was in the pursuit of "technological fantasies" like the electric car, he says.
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.
If the country's transportation fuel consumption is to fall by 10 per cent, Sivak and Tsimhoni calculate that the average fuel efficiency across the entire fleet will have to rise to 19.1 mpg.
President Obama announced in May that new cars should average 35.5 mpg (15.09 km/l) by 2016. But improvements to new cars could still leave the efficiency of the entire vehicle fleet largely unaffected without changes in policy, say Sivak and Tsimhoni.
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