The EPA is approving Ohio's submittal of a revision to the Ohio portion of the Cincinnati 1-Hour ozone maintenance plan. Ohio held a public hearing on the submittal on March 30, 2004. This maintenance plan revision establishes a new transportation conformity motor vehicle emissions budget (MVEB) for the year 2010. EPA is approving the allocation of a portion of the safety margin for oxides of nitrogen (NO<INF>X</INF>) to the area's 2010 MVEB for transportation conformity purposes. This allocation will still maintain the total emissions for the area at or below the attainment level required by the transportation conformity regulations. The transportation conformity budget for volatile organic compounds will remain the same as previously approved in the maintenance plan. EPA is not at this time addressing any request to redesignate the Ohio portion of the Cincinnati area to attainment for the 1-Hour ozone National Ambient Air Quality Standard (NAAQS). The rationale for the approval and other information are provided in this rulemaking action.