The Clean Air Act (CAA) requires that areas designated nonattainment or maintenance of a National Ambient Air Quality Standard (NAAQS) include transportation planning processes that are consistent with air quality goals included in approved state implementation plans (SIPs) for the areas. This is determined through the transportation conformity process. In short, the transportation conformity process is designed to demonstrate that transportation activities will not cause new air quality violations, worsen existing violations, or delay timely attainment of the NAAQS. More specifically, the transportation conformity process requires that any new or expanded local or state transportation projects clearly demonstrate that they fall below the motor vehicle emission budget (MVEB) included as maximum allowable emissions from mobile sources in the U.S. EPA approved SIP. If model-projected emissions of all transportation activities included in an area’s transportation plan are below the MVEB included in the approved SIP, the transportation plan is said to “conform” and transportation projects included in the plan can proceed towards completion.
- Cover Letter to U.S. EPA (June 4, 2010) [PDF]
- Approval and Promulgation of the Indiana Transportation Conformity Process and Procedures State Implementation Plan effective October 18, 2010
- Final Indiana Transportation Conformity Process and Procedures State Implementation Plan