Transportation conformity ensures transportation plans conform to air quality State Implementation Plans (SIPs) and don’t degrade air quality.
For areas that aren’t — or previously weren’t — in attainment of federal air quality standards, regional councils of government must project future population and vehicle travel growth resulting in motor vehicle emissions. We then use a U.S. Environmental Protection Agency (EPA) transportation/air quality model to project future motor vehicle emissions and compare these emissions with motor vehicle emission budget allowances contained in the applicable SIPs.
Emissions resulting from transportation plans mustn’t exceed the emission budgets in the applicable SIP.
The process is detailed in Colorado Air Quality Control Commission Regulation 10, Criteria for Analysis of Transportation Conformity.