In a memo issued this week, President Obama outlined that by 31 December 2015, all new light duty vehicles leased or purchased by federal agencies must be hybrid or electric, compressed natural gas or biofuel.  

He said: 'The federal government operates the largest fleet of light duty vehicles in America. We owe a responsibility to American citizens to lead by example and contribute to meeting our national goals of reducing oil imports by one-third by 2025 and putting one million advanced vehicles on the road by 2015.

'Living up to that responsibility means the Federal fleet should operate only as many vehicles as needed to work efficiently, leveraging Federal purchasing dollars to build manufacturing capacity for more alternative fueled vehicles, and reducing petroleum consumption through efficiency and alternative fuels.'

The memo also covers areas such as limiting vehicle body and engine size as well as options whilst ensuring that vehicles still meet needs.

The only vehicles exempt from the memo are those used for law enforcement, protection, emergency response or military tactical operations.

This week's has also seen the White House announce the introduction of new vehicle fuel-efficiency labels, intended to help drivers compare the costs of running an alternatively fuelled car and a conventional one.

The labels have been unveiled by the US Department of Transportation and the US Environmental Protection Agency.

'Today's car buyers want the best possible information about which cars on the lot offer the greatest fuel economy and the best environmental performance,' said EPA administrator Lisa Jackson. 'The new labels provide comprehensive information to American car buyers, helping them make a choice that will save money at the gas pump and prevent pollution in the air we breathe.'