Areas designated as air quality nonattainment or maintenance areas for the transportation-related pollutants have special meaning to transportation professionals. Transportation improvement projects in these areas must undergo a rigorous analytical process to demonstrate that they do not negatively impact air quality. In addition, there is a collaborative interagency consultation partnership between Federal agencies, the State DOT, and local government representatives that supports conformity analysis.

Transportation conformity ("conformity") is a way to ensure that Federal funding and approval goes to those transportation activities that are consistent with air quality goals. Conformity applies to transportation plans, transportation improvement programs (TIPs), and projects funded or approved by the Federal Highway Administration (FHWA) or the Federal Transit Administration (FTA) in areas that do not meet or previously have not met air quality standards for ozone, carbon monoxide, particulate matter, or nitrogen dioxide. These areas are known as "nonattainment areas" or "maintenance areas," respectively. Regulations governing transportation conformity are found in Title 40 of the Code of Federal Regulations (40 CFR Parts 51 and 93).

Hover over the highlighted Key Decisions to understand the specific relationship of transportation conformity to the decision. Click on any highlighted Key Decision for more information about questions, data, and relationships that support this interface. Key Decisions that are greyed-out have no specific relevance to the individual application or topic area but are still accessible from this graphic.