Guardian: Barack Obama is to compel US car makers to give up on gas guzzlers and step up production of a more fuel-efficient vehicle fleet. In a ceremony today at the White House, Obama will establish the first national limits on car exhaust and dramatically raise fuel efficiency standards. The new exhaust target – an average 35.5mpg by 2016 – will force US manufacturers to produce cars and trucks that are nearly 40% more efficient. Environmentalists said the new standards will do more …