EPA is approving a State Implementation Plan (SIP) revision submitted by New Jersey that consists of two elements necessary for EPA to grant final full approval of New Jersey's enhanced motor vehicle inspection and maintenance (I/M) program. The first element provides the State's final submittal for compliance with the National Highway Systems Designation Act (NHSDA), which allowed states to claim additional credit for their decentralized inspection and maintenance programs, provided they could validate that credit claim with actual program implementation data. The second element revises New Jersey's performance standard modeling to reflect the State's enhanced I/M program as it is currently implemented. This element satisfies a condition of EPA's May 14, 1997 conditional interim approval of New Jersey's enhanced I/M program SIP. The intended effect of this action is to approve the two evaluations of the enhanced I/M program, in addition to prior minor revisions to the enhanced I/M SIP, and to grant final full approval of the program. The enhanced I/M program will result in emission reductions that will help achieve attainment of the one-hour ozone standard and carbon monoxide standard.