In November 1993, EPA promulgated two sets of regulations to implement Section 176(c) of the Clean Air Act. First, on November 24, EPA promulgated the Transportation Conformity Regulations, which apply to highways and mass transit. These regulations establish the criteria and procedures for determining whether transportation plans, programs, and projects funded under title 23 U.S. C. or the Federal Transit Act conform with the State Implementation Plan (SIP) (58 FR 62188).

Then, on November 30, EPA promulgated a second set of regulations, known as the General Conformity Regulations, which apply to all other federal actions. These regulations ensured that other federal actions also conformed to the SIPs (58 FR 63214).

Final revisions to the General Conformity Regulations were published March 24, 2010.

• Promulgated Transportation Conformity Regulations (PDF)(67 pp, 14 MB, November 24, 1993, 58 FR 62188)
• Promulgated General Conformity Regulations (PDF)(48 pp, 5 MB, November 30, 1993, 58 FR 63214)
• Revisions to the General Conformity Regulations (PDF)(134 pp, 447 K, March 24, 2010, 40CFR Pts 51 and 93)