That view is not universally shared by the great American public, however. Industry officials say that while many are keen to downsize, this shift from large to smaller cars is motivated more by fuel prices than by concerns about the environment.

Volkswagen is cautious about introducing new technology too quickly
"Consumers are being very careful about how they spend their money," observes automotive consultant Michael Robinet of CSM Worldwide.
Tighter emission regulations are also driving change. President Obama recently said the industry must build cars that deliver an overall average of 35.5 miles per US gallon (42.6 mpg imperial) by 2016, rather than by 2020 as previously planned.
"The composition of our market is going to change quickly because of the federal mandate," predicts David Zuchowski, vice-president of Hyundai in the US.
"Our industry is going to become more like the European industry in the next couple of years, with more smaller cars."
But the shift away from big "gas-guzzlers" could take a long time, Edmunds.com automotive analyst Jeremy Anwyl says.
The number of electric or petrol-electric hybrids sold in the US "will still be modest" for some time yet when compared with overall sales figures, he reasons.
Risk of failure
Volkswagen's research and development chief Ulrich Hackenberg agrees, describing rival carmakers' electric vehicle launches as "hype".
"Some manufacturers are already releasing their e-cars on customers," he says. "We are only using test fleets."
The X Prize organisers feel the conventional automotive industry could do more to speed things up.
"We hope automakers will take another look at our mission and see just how closely it aligns with their goals of bringing new, affordable and fuel-efficient technology to drivers," says Mr Diamandis.
And there are good reasons why the industry is moving slowly, according to HSBC analysts Horst Schneider and Niels Fehre.
"Unreliable or unsafe technology would damage the image of electric vehicles and of their manufacturers," they say.
We can understand the wait-and-see stance of the mass-market leader, Volkswagen."