Mass transit projects proposed for federal funding must meet the
requirements of the Clean Air Act in addition to NEPA. The Clean
Air Act contains detailed transportation “conformity”
requirements the purpose of which is to ensure that federally-
funded highway and transit projects conform to the applicable
State (air quality) Implementation Plan (SIP). The SIP documents
the measures that will be taken in a specific nonattainment area
in order to attain the national air quality standards. The
conformity requirements apply only in nonattainment and
maintenance areas. The conformity process is governed by a
regulation issued by the Environmental Protection Agency (40 CFR
Part 93). EPA’s Office of Transportation and Air Quality has
also issued numerous guidance documents and materials related to
the conformity process which can be found in the Conformity
section of the following website: Environmental Protection
Agency - Transportation Conformity. A different office in EPA
has responsibility for setting and revis