President Barack Obama has reversed a Bush-administration regulation preventing states from determining their own policies regarding transport emissions.
The rule change will allow states to set stricter emissions rules, allowing California and thirteen other states to implement their own policies. In December 2007 President Bush reversed a decision to allow states to set their own pollution rules, instead establishing a much less tough national emissions standard.
California will now look to introduce a more stringent set of rules than the curernt Federal Clean Air Act, which will itself require a 30 per cent reduction in vehicle emissions by 2016.
In the same speech, President Obama also instructed the Department of Transportation to come up with a stricter set of fuel economy and emissions targets for manufacturers by March.
Future regulations will also require new cars and trucks to achieve an average of 35 US miles per gallon by 2011, a move previously outlined by President Bush with a provisional 2020 deadline.
Several manufacturers will now have to lower the emissions levels of their cars by up to 40 per cent if they are to meet the new targets.