The Trump Administration’s proposed fuel economy standard rollback and emissions standards freeze will harm consumers and the environment. This research note finds the proposal would cost the U.S. economy up to $400 billion through 2050, while increasing U.S. emissions up to 10% and gasoline use up to 7.6 billion barrels through 2035. It would also cost the Canadian economy up to $70 billion through 2050 and increase Canadian emissions up to 11% by 2035.