A study was conducted to determine potential improvements in automobile fuel consumption based on innovative design and components. Standard and compact-size reference vehicles were selected, and a study of how power is used was conducted. Obvious technological innovations (e.g., powerplants, transmissions and drive train systems, tires, accessories and auxiliaries, aerodynamics, and weight) that would save on fuel consumption were identified and evaluated, and then screened against program constraints. This volume is the main body of the report and provides a comprehensive discussion of each improvement option, the Government constraints, the synthesized vehicles and the possible fuel economy gains. The contents cover: Fuel economy versus governmental constraints, operating conditions, and user/market requirements; fuel economy technology; the synthesis and evaluation of alternative vehicle designs.