General Motors' on again, off again rear-wheel drive sedan plans are, well, off again. The U.S.' largest automaker has been mulling over a rear-wheel drive Chevrolet Impala and a rear-wheel drive Buick sedan, but both plans have been canceled due to newly passed CAFE regulations.

A source familiar with GM's plans revealed to Automotive News that GM had actually planned to release a rear-wheel drive Impala in 2011. The design featured a long hood and short decklid and was about 3 inches longer than the front-wheel drive 2008 model.

The source also revealed that the rear-wheel drive Impala was slated to get an SS version, which would have featured a V8 producing more than 350 horsepower.

However, the 35 mpg CAFE regulations have forced GM to scrap its large rear-wheel drive plans. Both of the canceled models were slated to ride on the same Zeta platform that underpins the Pontiac G8 and the upcoming 2010 Chevrolet Camaro.