Diesel primary power plus an on-board electric power generation with a discharge-recharge electric cell array, using individual drive motors at each wheel, would seem to be an even better engineering "elegant answer" than the gasoline-powered units now on the road. Presently, the weak point is the deep-cycle batteries necessary to take full advantage of regenerative braking and "burst" power demands of acceleration. The best current designs are still prone to overheating during charge or discharge, and potential catastrophic failure (exploding or bursting into flame).
One alternative I have sort of mulled over, is instead of an electrical component being used to transmit power from the primary power unit to the wheels, is to use a hydrostatic system, with an accumulator tank, some form of compressed gas over the hydraulic medium. The primary power unit would drive a hydrostatic pump, which would first build pressure to the accumulator, then from the accumulator, meter out the power to each individual hydrostatic wheel motor. By reversing the valving in the hydrostatic motor, it could be used for its braking effect, pumping the pressure back to the accumulator.
Because of the great flexibility of the system, the center of gravity could be placed quite low, without consideration for transmission or axle clearances, as the hydrostatic motors would be placed near the wheel hubs. In fact, each hydrostatic motor could be fitted with a planetary gearset, allowing both low-speed, high-torque application, and high-speed cruising with minimal power input. Everything would be controlled with electronic sensors that would increase or decrease the pressure applied to each of the wheel motors as conditions warrant.
All this with a small Diesel engine, running at a near-constant speed, staying within a very narrow RPM band. The engine could be fine-tuned for maximum economy in this very narrow band (excessive engine output would seem sort of redundant with this design), and the overall economy is much less affected by "heavy-handed" driver characteristics. If you want more power for a burst of acceleration, let the accumulator build a little more first. Rather like getting up a "head of steam" on an old steam locomotive. The throttle would control how much pressure is being sent to the hydrostatic motors, not engine speed. When the pressure has accumulated to a sufficiently high level, the engine could even be shut off for varying periods of time, and restarted as the pressure dropped below a certain point.
We are not done inventing personal transportation yet.
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