The two-mode system is designed to operate at maximum efficiency in both city and highway driving, GM says. Most current hybrid systems improve efficiency the most in stop-and-go driving. That's why cars like the Toyota Prius have higher EPA fuel economy ratings for city driving than highway driving, just the reverse of most cars. GM promises a 25-percent improvement in overall fuel economy.
Another advantage of the two-mode system is that it is incorporated into the vehicle's transmission tunnel making it less expensive to produce hybrid versions of vehicles.