They do, wolfy, but you can achieve the same thing with the new "power efficient" gas models (using almost the exact same principle, too!). Our county switched over to those for all of the non-emergency official vehicles, and it hasn't changed much of anything. They are great for conserving energy, though, because the re-wiring basically lets your car shut down every time you come to a stop (not a stop-sign stop, but a stop at a stoplight or something).
Basically, what it does is harvest the energy lost every time you break, and store that in an extra battery, which it draws down regularly. It is a completely self-charging mechanism, but it is essentially a more conservative model of gas vehicle. If you want to get a more efficient type of car, the hybrids/power efficient models are really good options, but they are still gas reliant and definitely reflect the prices at the pump.
Can I just site here that I love the key mechanism on the hybrids? I don't know if it is on all hybrids or just the county's, but instead of having a metal key, they have key "fobs" that you basically leave in your pocket. The car senses if someone with its fob is close, and you can control it completely with the fob. You can still open the door with a normal key, but you have to have the fob to be able to start and drive the vehicle. If you walk away from the car, the car will automatically lock and power down when the fob gets a certain distance away. Not too handy if you have pets/etc in the car, but other than that, I think it is an absolutely great advancement, and I wish my car had it.
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