The Environmental Protection Agency (EPA) is taking final action to conditionally approve a revision to the State of Nevada's state implementation plan (SIP) for Clark County. The revision consists of an update to certain elements of the maintenance plan for the Clark County air quality planning area for the 1997 8-hour ozone national ambient air quality standards (NAAQS), including the emissions inventories, maintenance demonstration, and motor vehicle emissions budgets. The EPA is conditionally approving the SIP revision because the SIP it continues to provide for maintenance of the 1997 ozone NAAQS; upon fulfillment of certain commitments, it will not interfere with attainment or reasonable further progress of the other NAAQS; and the budgets meet the applicable transportation conformity requirements. The approval is conditional because it is based on commitments to submit an additional SIP revision to reduce the safety margin allocations for the budgets within one year of this final conditional approval.