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Starting with the tractive energy requirements of vehicles over prescribed driving schedules, the fuel economy potential of idealised heat engine/flywheel hybrid vehicles was established as a function of vehicle characteristics and driveline efficiency. Both passenger cars and busses were considered in this analysis. The calculated idealized hybrid fuel economies were compared with cur rent production vehicle fuel economies and the potential for substantial fuel economy improvement was noted. When the hybrid vehicle is penalized for the initial flywheel-charge energy, the potential economy gains are reduced. The effect of the initial charge energy should not be neglected in passenger car driving schedules. However, the effect is minimal for the urban schedules typical of bus service.

The existence of the computer coupled with the rapid development of analytical engineering techniques has made it possible to design complex systems which are different and better, and to do so in a manner that is more efficient. Examples from the aircraft industry include hypersonic airplanes in which the fuel serves as a coolant to heat sensitive frame components, and the frame serves as part of the engine. Thus, design changes to any single part have cascading effects on the entire Bystem. This leads to extreme complexity in the design process and requires extensive computational resources and sophisticated computer techniques to proceed in a rational manner. For example, large scale systems theory and multi-level optimization are some of the approaches applicable to this class of design problems.