Want to know the fuel economy ratings of a new car you’re considering? You probably already know to look at the gas-mileage window sticker. Now, for the first time in 30 years, the US Environmental Protection Agency and the National Highway Traffic Safety … For a plug-in hybrid , the designs provide both the gas mileage when operating in gasoline mode and the energy usage (in kilowatts per 100 miles) when operating in electric mode. …. More from Green Car Reports …