The U.S. Department of Transportation issued a final auto fuel economy rule on September 28. According to Sina Finance, the regulator estimated that the new standard would put the average fuel economy for 2031-model-year passenger cars and light trucks at about 34.9 miles per gallon, below the 50.4 mpg expected under the 2024 rule.

The rule also changes vehicle classification and will end fuel-economy credit trading between automakers. The National Highway Traffic Safety Administration said the rule revises standards for 2022 through 2031 model-year passenger cars and light trucks, and its estimate still puts the 2031 fleet average above the 30.1 mpg level for the 2024 model year.

The Transportation Department said the current classification system encourages some automakers to redesign vehicles so they can be placed in the less stringent light-truck category. The new rule will end credit trading starting with the 2028 model year and change the classification standards for passenger cars and light trucks starting with the 2030 model year.

The department estimated that the rule could cut the average price of a new vehicle by about $1,300 and generate about $138 billion in savings over the next five years. According to Sina Finance, those figures are government estimates of policy effects, while actual prices will still be determined by automakers and the market.