The most significant alteration is issuing specific protocols governing the coast-down test, according to Automotive News. The examination gathers data on things like drag, rolling resistance and drivetrain friction as a vehicle cruises from 80 miles per hour to a complete stop. That information is then used to program dynamometers for further driving analyses, but currently, the exact procedure varies by company. Inaccurate figures from the assessment were reportedly responsible for Hyundai and Kia's fuel economy mark down and one of the changes for the Ford C-Max.
The other big change closes a loophole that allows automakers to test the fuel economy for a single model and then apply it to others with the same powertrain and weight class. This is the same issue that forced Ford to re-rate the C-Max in 2013.
According to Automotive News, the agency is also planning to continue with successful policies like auditing the fuel economy of more models to make sure they match manufacturers' ratings. It may also force companies to double-check mileage results from pre-production examples against the final version of a vehicle.