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Transportation Conformity: A Basic Guide for State & Local Officials

Transportation Conformity and Actions Subject to Conformity

Transportation conformity is a process required by the CAA Section 176(c), which establishes the framework for improving air quality to protect public health and the environment. The goal of transportation conformity is to ensure that FHWA and FTA funding and approvals are given to highway and public transportation activities that are consistent with air quality goals.

The CAA requires that metropolitan transportation plans, TIPs, and Federal projects conform to the purpose of the SIP. Conformity to a SIP means that such activities will not cause or contribute to any new violations of the NAAQS; increase the frequency or severity of NAAQS violations; or delay timely attainment of the NAAQS or any required interim milestone. Conformity requirements apply in areas that either 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. For a complete list of nonattainment and maintenance areas for these and other pollutants see 40 CFR Part 81 or www.epa.gov/green-book.

Pollutants that Come from On-Road Vehicles (e.g., Cars, Trucks, Buses) Transportation sources contribute to four of the six criteria pollutants for which EPA has established standards to protect public health and/or safety. The pollutants are: ozone (O3), carbon monoxide (CO), particulate matter (PM10 and PM2.5), and nitrogen dioxide (NO2). Appendix A provides basic facts about health impacts of these pollutants. Exhibit 2 shows the proportion of PM10, PM2.5, nitrogen oxides (NOX), volatile organic compounds (VOCs), and CO emissions from the various sources of pollution. Exhibit 3 shows the on-road percentage of total emissions by pollutant in 2011.

EXHIBIT 2

Proportion of PM10, PM2.5, Nitrogen Oxides (NOX), Volatile Organic Compounds (VOCs), and CO Emissions from the Various Sources of Pollution

Pie chart shows that in 2013, 2% of PM-10 emissions were from on-road vehicles, 1% were from non-road vehicles, 5% were from stationary fuel combustion, 6% were from industrial and other processes, and 87% were from miscellaneous sources.

PM10 Emissions 2013

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries

*Miscellaneous sources include prescribed fires and wildfires, dust from paved and unpaved roads, road construction, and agriculture operations.

Pie chart shows that in 2013, 3% of PM-2.5 emissions were from on-road vehicles, 3% were from non-road vehicles, 14% were from stationary fuel combustion, 9% were from industrial and other processes, and 71% were from miscellaneous sources.

PM2.5 Emissions 2013

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries

*Miscellaneous sources include prescribed fires and wildfires, dust from paved and unpaved roads, road construction, and agriculture operations.

Pie pie chart shows that in 2013, 38% of NO<sub>x</sub> emissions were from on-road vehicles, 21% were from non-road vehicles, 28% were from stationary fuel combustion, 10% were from industrial and other processes, and 3% were from miscellaneous sources.

NOX Emissions 2013

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries

Pie chart shows that in 2013, 14% of VOC emissions were from on-road vehicles, 11% were from non-road vehicles, 4% were from stationary fuel combustion, 41% were from industrial and other processes, and 30% were from miscellaneous sources.

VOC Emissions 2013

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries

Pie pie chart shows that in 2013, 34% of CO emissions were from on-road vehicles, 21% were from non-road vehicles, 7% were from stationary fuel combustion, 4% were from industrial and other processes, and 34% were from miscellaneous sources.

CO Emissions 2013

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries

EXHIBIT 3

Emissions from On-Road Mobile Sources as Percentage of All Sources for Each Pollutant in 2013

The emissions from on-road mobile sources as percentage of all sources for each pollutant in 2013. The bar graph shows the percentage of on-road mobile source pollutants relative to all sources of the individual air pollutant in 2013. The pollutants shown are PM-2.5. PM-10, NO<sub>x</sub>, VOC, and CO. The chart indicates that on-road mobile sources contribute 3 percent of all PM-2.5 sources, 2 percent of all PM-10 sources, 38 percent of all NO<sub>x</sub> sources, 14% of all VOC sources, and 34 percent of CO pollutant sources

U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries

Updated: 5/16/2017
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