These areas are known as "non-attainment areas" or "maintenance areas," respectively. A conformity determination demonstrates that the total emissions projected for a plan or program are within the emissions limits ("budgets") established by the air quality plan or State Implementation Plan (SIP), and that transportation control measures (TCMs) are implemented in a timely fashion.

Determining Conformity
Regional emissions are estimated based on highway and transit usage according to transportation plans and TIPs. The projected emissions for the plan and TIP must not exceed the emissions limits (or "budgets") established by the SIP. Also, the MPO is required to demonstrate that TCMs are implemented in a timely fashion.

The Decision Process
A formal interagency consultation process involving the Environmental Protection Agency (EPA), FHWA, FTA and State and local transportation and air quality agencies is required in developing SIPs, TIPs, and transportation plans, and in making conformity determinations. Metropolitan Planning Organization (MPO) policy boards make initial conformity determinations in metropolitan areas, while State Departments of Transportation (DOT) usually do so in areas outside of MPOs. Conformity determinations must also be made at the Federal level by FHWA/FTA. These determinations must be made at least every three years, or when transportation plans or TIPs are updated.

Conformity analysis is made available to the public as part of the MPO and/or State DOT planning processes. MPOs are required to make transportation plans, TIPs, and conformity determinations available to the public, accept and respond to public comments, and provide adequate notice of relevant public meetings. Project sponsors must also include appropriate public involvement during project development.

Emissions Budget
The SIP places limits on emissions of each pollutant for each source type (mobile, stationary and area sources). Projected emissions from highway and transit usage must be less than or equal to the emissions limits for on-road mobile vehicles that are established by the SIP. These emissions limits for motor vehicle emissions sources are called "budgets." Budgets are developed as part of the air quality planning process by State air quality/environmental agencies, and approved by EPA. Transportation agencies participate in this process.

Transportation Control Measures (TCMs)
Areas can include TCMs in their SIPs. TCMs are specific programs designed to reduce emissions from transportation sources by reducing vehicle use or changing traffic flow or congestion conditions.

Programs for improving public transit include:

• developing high occupancy vehicle (HOV) facilities
• ordinances to promote non-motor vehicle travel
• transit improvements
• signal timing
• bicycle and pedestrian facilities
• land use planning

Overview of the Conformity Process

• Overview of the Conformity Process (800 KB)