Americans may be over their love of big, gas-guzzling automobiles as 83% of the top trade-ins under the Obama administration's �cash for clunkers' scheme have been SUVs or pick-up trucks. The new scheme to boost auto sales has proved popular, with 316,189 cars worth $1,326m (�802m) turned in during the first two weeks. Statistics provided by the Department of Transport suggest that Americans are now fleeing from SUVs, which reached their peak in popularity in the middle of this decade. Six of the top 10 trade-ins were SUVs, with two mini-vans and two pick-up trucks rounding off the list. The reject list did not include any sedan model cars. The scheme, which was designed primarily to boost auto sales rather than green America's roads, does not require purchasers to make a radical improvement in fuel-efficiency in their new car. But the Obama administration claimed that the programme was getting the dirtiest vehicles off America's roads, saying that customers were going home from dealerships with new cars that were on average 63% less polluting. However, environmentalists say it's far from clear whether the scheme will significantly reduce the carbon emissions from cars and � even if it does � it's a very costly way to achieve such benefits, at about $500 for each tonne of carbon eliminated. "We think there will be some emissions reduction but it will just be a very small percentage of emissions from transportation," said Chris Ganson, a transport analyst at the World Resources Institute (WRI). "It's still just a drop in the bucket." An analysis by WRI found that the scheme would save less than two days' worth of carbon emissions between now and 2019. The scheme pays customers up to $4,500 to turn in their old, polluting vehicle, and the replacement vehicle only has to achieve a 4mpg improvement on the clunker. All but two of the cars on the top 10 list of purchases are sedans, and the fourth most popular car purchased under the scheme is the Toyota Prius.