In 2004, the Environmental Protection Agency launched a program called SmartWay to work with freight supply chain operators (think freight trucks) to find ways to maximize their fuel efficiency and lower emissions. Recently, SmartWay has expanded into the rental car market to encourage companies to rent out cars that are the most fuel-efficient in their category. When renting a car, look for SmartWay-certified ones to help you save fuel and money with your rental. A general rule of thumb is this: Most vehicles in economy, compact and intermediate classes are SmartWay certified. But when in doubt, ask.