New York, New Jersey, Pennsylvania, Connecticut, and California disagreed with NHTSA that U.S. law (49 U.S. Code § 32919) precludes state-level light vehicle greenhouse gas regulations because such regulations are related to fuel economy standards. While NHTSA indicated that fuel economy is calculated by measuring vehicular carbon emissions and that nearly all of the engineering options to reduce vehicular GHG emissions also improve fuel economy, these states argued that because that the use of alternative fuels could allow greenhouse gas emissions to be reduced somewhat independently of fuel efficiency, greenhouse gas standards are not related to fuel economy standards.