Not even the most optimistic greens could have predicted that the federal government’s cash-for-clunkers program would work this well — more than 240,000 Americans have traded in their clunkers so far, and the program has already burned through its first round of funding. But green groups were a bit wary of cash for clunkers at the outset, concerned that the legislation’s requirements on fuel economy were too lax. Under the program, newly purchased passenger cars must have a minimum fuel-economy rating of 22 miles per gallon — hardly superefficient — and they need to be only 4 m.p.g
