EPA proposed to partially approve and partially disapprove California’s submission to revise its State Implementation Plan (SIP) relating to the control of emissions from non-gasoline combustion vehicles over 14,000 pounds. Specifically, EPA proposed to disapprove California’s SIP revisions as applied to vehicles registered out of state, or out of country. EPA cited “substantial concerns” that California has not provided adequate assurances under Clean Air Act section 110(a)(2)(E)(i) that implementation of this SIP is not prohibited by Federal law.