Hybrid cars are defined by having an electric motor as part of their propulsion system, either as an assist to the gasoline engine (as with the Honda design) or as a separate, lower-speed drivetrain (as with the Toyota and Ford designs). But the electric motor isn't the only element that makes a hybrid efficient. A feature which almost seems like an aside actually accounts for a decent amount of fuel (and emissions) savings: the engine is turned off whenever the vehicle comes to a stop, so there's no sitting and idling. Once the brake pedal is released, the engine comes right back on, with no noticeable delay.
(Although the engine of my Honda Civic Hybrid is quiet, the sudden silence when "auto-stop" kicks in is hard to miss. I've actually had pedestrians tell me that my "car died" while walking in front of me.)
It turns out that the technology for shutting off the engine while stopped does not require the rest of the hybrid system. What's more, alone it can still result in notable improvements in fuel efficiency and emissions reductions. PSA Peugeot Citroën has announced its "Stop & Start" technology, which reduces fuel consumption by 15% in heavy traffic, 10% in city driving, and 6% in "combined cycle" use (city and highway driving, where stopping is less common).
The auto-stop feature is one of two standard hybrid technologies which could result in significant fuel savings if used in non-hybrid vehicles. The other is the mileage readout. Having a real-time indicator of how one's driving affects one's fuel consumption is simultaneously a trigger for competitive, "got to get that number higher" urges and a beautiful example of making the invisible visible. Most people don't know what kind of mileage they get in their cars, or at best assume that the EPA estimates are right (they're not). I know that I've changed my driving habits because of the readout in my hybrid, and anecdotal evidence suggests I'm far from the only one.