Plans for vehicles based on General Motors' rear-wheel-drive Zeta platform have been set back due to proposed legislation to cut emissions in the US.The new legislation requires a 30 per cent increase in corporate average fuel economy (CAFE) by 2017; a target that would be difficult to achieve with a number of powerful rear-wheel-drive vehicles in production. Thankfully, the much-anticipated Chevrolet Camaro is still going ahead for production in 2009 due to its late stage of development. The future is less certain for any other rear-wheel-drive models that GM has planned, including a Chevrolet Impala saloon, Buick sedan and the baby Cadillac coupe.Yet this new proposal doesn't seem to be troubling Ford, which is planning more rear-wheel-drive models using an all-new platform. Said to be with us before 2012, the details of these models have not been revealed yet, but the Interceptor saloon concept that was revealed at Detroit this year is a likely candidate for first release.Which of the US car giants is making the right decision is hard to say. Vice chairman of General Motors, Bob Lutz, has said that "we will decide on our rear-drive cars when the government decides on the CAFE regulations", so nothing is definite regarding GMs plans until the legislation is passed.However, with Ford proposing more new models based on a whole new platform, GMs status can't remain static for long.