Do you suppose the distance traveled by the dead driver after this thing explodes is already included in the estimated mpg?

You must admit, the idea of ramming things to get bonus energy has some appeal, in a limited, video-game-esque sense.

Ditch the hydrolics, designed correctly, flywheel engines automatically feed energy lost in braking back into the system:

In all present road vehicles, braking is achieved by an absurdly crude and wasteful method: The kinetic energy of the vehicle is turned into heat by friction in the brakes, whence it is quite literally thrown into the wind. Not so in a flywheel vehicle. Here braking can be accomplished by reversing the motor generator functions. The wheels of the vehicle to be decelerated drive the motor (now used as a generator), which generates current to turn the flywheel generator (now used as a motor) and this will rev up the flywheel; the generator on the wheel axle is thereby subjected to a heavy load as it delivers a large current, and this will brake the vehicle. Thus, the excess kinetic energy of the vehicle is not turned into useless heat, but into additional kinetic energy of the flywheel. It is like a man returning from a trip who puts his unspent money back into the bank instead of flushing it down the toilet.

I first got turned on to the idea in the way back when I read an article in Discover magazine regarding an inventor who seemed to have built the perfect method of using flywheels to power a vehicle. I just went and dug up the article, eleven years later the idea still has merit and all the previous drawbacks (including safety) seem to be covered:

Spin-up tests, Bitterly says, confirmed that their flywheels were working as designed. The whole system, in fact, was soon working as designed. Everything was custom-made, including test instruments. A wheel being tested gets a shiny silver coating; laser pulses reflecting off its surface measure the wheel's expansion as it revs up to speed. Some 95 "data stations," including 100 laser sensors that the Bitterlys invented, monitor wheel growth, temperature, the current flowing through the magnetic bearings, et cetera. These instruments must work at exceptionally fast speeds, like the electronic components in magnetic bearings. "This is where we outshine the world," Bitterly says, surprisingly: custom-built instrumentation. He documents every wheel's performance in exhaustive tests, similar to the ones used for new airplane engines. "You don't just run it up to speed," he says, laughing, "and say, `Hey, it's done.'" Watching the data come in from a test, Bitterly can choose to burst a wheel or shut it down before failure. His instruments show him where fibers will start to separate, and the speed at which the wheel will break. Failure, by the way, is difficult to achieve; his wheels survive considerably higher speeds than 100,000 rpm. And Bitterly has never broken one during a test; the equipment is too expensive. Safety, however, requires such tests. "It's common knowledge already," he grumbles, "that you don't get shrapnel from fiber wheels." A fiber wheel's kinetic energy dissipates, instead, into hot fluff and high-speed dust. But an explosion of hot dust is still a sort of minivolcano; it must be safely contained.

Flywheel designers recently began to pool their experimental information on safety. So far, they agree that the best approach is simply to build adequate containers. Almost any container at all, Bitterly suggests, would make fiber wheels safer than, say, the massive, shrieking steel turbines in jet engines, next to which unknowing airline passengers routinely sit for hours. Even in cars, people blithely ignore a more hazardous material. Gasoline, Bitterly points out, has more concentrated energy than rapidly spinning flywheels, and it is easily ignited.

The line of technology described in the Discover article doesn't seem to be applied to any of the current articles I'm finding on the subject of flywheel auto motors, this article, dated nearly 10 years later, still cites all the drawbacks that the technology described in the Discover article claims to have overcome.

Yawn. Wake me when he has a running prototype. He may want to talk to Citroen about the hydraulics thing.

You think this is dangerous, would you believe that there are vehicles out there that carry around tanks of volatile, low flashpoint hydrocarbons? Some of these carry 20, 30, or even more gallons of the stuff. Imagine what could happen to that in a collision!

Worse, there are nutcases out there who buy these things to drive their children around!