 Some, like the Chevrolet Volt, can operate in all-electric mode without using gasoline, and others operate in a blended mode like the Toyota Prius PHV, which uses both energy stored in the battery and energy from the gasoline tank to propel the vehicle, but that can deliver substantial all-electric driving in blended mode.In addition, since the all-electric range of plug-in hybrids depends on the size of the battery pack, the analysis introduced a utility factor as a projection of the share of miles that will be driven using electricity by an average driver, for both, electric only and blended EV modes.Since all-electric cars do not produce tailpipe emissions, the utility factor applies only to plug-in hybrids.