Several drivetrain layouts were considered during early development, including rear and mid-engine designs, but most were dismissed because of technical and legislative difficulties. Having the engine, transmission, catalytic converter(s) and exhaust all cramped into a small rear engine bay made emission and noise control difficult which were the problems Porsche had with the 911. After deciding that the mid-engine layout did not allow enough room in the passenger compartment, a front-engine, rear-wheel drive layout was chosen. Porsche may have feared that the U.S. government would soon ban the sale of rear-engine cars in response to concern over safety problems with the rear-engine Chevrolet Corvair.