- General Motors and Stellantis ranked among the worst automakers in average estimated real-world fuel economy and carbon emissions, according to the EPA.The Detroit automaker's average estimated real-world fuel economy and its carbon emissions ranked the second-worst in the industry for the 2021 model-year, according to the EPA.Both automakers decreased their fuel economy and increased C02 emissions since the 2016 model-year, according to the EPA, as did Hyundai Motor, Mazda and Volkswagen.Ford Motor, which ranked just above GM, slightly improved during the five-year timeframe but remained below the industry averages.Toyota Motor, which popularized the hybrid segment with its Prius, has been criticized by some politicians and environmentalists for not moving to EVs more quickly."