How does the process of air quality and transportation conformity work?
Since 1991, with the passage of the Intermodal Surface Transportation Efficiency Act (ISTEA) and subsequent update of the act in 1998 (The Transportation Equity Act for the 21st Century) known as TEA-21, metropolitan area transportation plans have been required to show conformity with federal Clean Air Act standards. Under the Clean Air Act, every state must submit a State Implementation Plan (SIP) that shows how it will manage and reduce levels of major pollutants that are in violation of federal air quality standards. This includes ground-level ozone and particle pollution. The SIP sets an overall budget for allowable emissions for each pollutant in violation and allocates these emissions for each sector, including transportation. Thus, transportation plans must show they will contain emissions within a certain level. Failure to do this results in what is known as a “conformity lapse” (meaning that the transportation plan does not conform to its emissions threshold). Any region in a
