Just read about the big change coming in U.S. model Smart Fortwos beginning, hopefully, with September 2008 production models. This is from Popular Mechanics:
The Micro Hybrid Drive
"The Micro Hybrid Drive (MHD) isn't a hybrid in the accepted sense of the word. The drive doesn't "drive" the car, and doesn't power the air conditioning. This "hybrid" unit is a beefed-up, belt-driven alternator/starter, which simply powers the stop/start function by recharging the battery on over-run and restarting the car quickly. The 70 horsepower, one-liter gas engine cuts out as the car rolls to a stop at under 5mph. And it automatically starts again as soon as you take your foot off the brake pedal.
It's a simple system that has a big fuel consumption benefit. Mercedes reckons the MHD Smart will return 54.7 mpg (US) in the EU Combined cycle, which is an eight percent improvement. Fuel savings could be as high as 19 percent in crowded city streets. In use, it's almost pain-free. Restarting involves a little more noise and vibration than the equivalent system on BMW's bigger diesel MINI. This is not such a bad thing, however, as there is at least the confidence that the engine is actually running when the lights change and you put your foot on the throttle.
The system will be fitted to all non-diesel Smarts from September this year, although the company is vague as to whether US Smarts will get the drive immediately.
We hope they do: it seems like such an eco no brainer. Just imagine if every engine in Los Angeles was stopped as soon as its speed dropped below 5 mph.
What would that do for fuel consumption? Or air-born particulate emissions?
How much sweeter the air would be, how much quieter the sidewalk."