A study was made to conceive and evaluate a flywheel/electrical transmission system. The investigation encompassed several machinery and electronic options, and each transmission option was evaluated and ranked according to cost, weight, and fuel economy. The vehicle used for the evaluation was a five-passenger family sedan. The primary use of this transmission system is to augment the heat engine with energy from the flywheel in such a manner as to level engine loads and improve the overall vehicle efficiency. It was determined that the ac--ac transmission system is the most attractive for vehicular applications in the weight range investigated. A comparison was made between a conventionally propelled (heat engine/automatic transmission) vehicle and the same vehicle configured with the hybrid propulsion arrangement that utilized the selected ac--ac transmission system. The results of this comparison are shown. The conventional vehicle has a curb weight of 3000 lb, whereas the same vehicle configured with the hybrid arrangement has a curb weight of 2866 lb. Both vehicles have the same acceleration and pass maneuver performance. The capability for steady-state hill climb of a 5% grade, which established the heat engine size, is limited to 55 mph for the hybrid vehicle. This is in compliance with study requirements. The hybrid's fuel consumption is 39.5 mpg, compared to 15 mpg projected for the conventional vehicle. This represents a 263% improvement and also exceeds any postulated Federal economy standards. The hybrid also provides a 40% savings in direct operating cost to the consumer. These benefits are derived for a $2330 increase in vehicle retail (sticker) price. (ERA citation 03:044971)