The CAA has established procedures and limitations for evaluating transportation projects in  areas within the U.S. designated as nonattainment or maintenance 83  with respect to the NAAQS.  The specific procedures, often referred to as Transportation Conformity regulations (see  Section  8 ,  Conformity),  require assessment of potential air quality impacts of all regionally significant  planned and programmed transportation projects. The transportation conformity regulations for  localized CO and PM hot-spot analyses are codified within 40 CFR Part 93, Subpart A 84 .  In addition to the conformity regulation requirements, NEPA also requires environmental review  of actions that have the potential to affect  the environment (see  Section 2 ,  Regulatory  Framework ). Specifically,  on-road transportation projects using federal -aid funds and/or  requiring Federal Highway Administration (FHWA) or the Federal Transit Administration (FTA)  approval actions must be evaluated for the potential impacts the actions will have on the natural  and human environment. Air quality is one of several elements within the human environment to  be considered. The NEPA requirements in regard to project -level FHWA/FTA air quality  analyses are outlined in 23 CFR Part 771. 85  The major difference between the project -level air quality requi rements under the CAA and  those under the NEPA is that CAA hot -spot requirements apply to projects within specifically  identified areas ( i.e., nonattainment/maintenance areas), whereas NEPA applies to federally - funded projects irrespective of location.  When conducting a hot-spot analysis for the purposes of complying with NEPA or transportation  conformity, the EPA -preferred/recommended dispersion and emission  models 86  are the  CAL3QHC/CAL3QHCR and AERMOD, and MOVES /EMFAC (see  Section 5 ,  Air Quality  Assessment Models ), respectively.  NEPA air quality analyses have typically focused on CO as the primary indicator for vehicular  air quality impacts. A CO project -level hot-spot analysis is performed to ensure that new or  worsened violations of the NAAQS will not occur as a result of  a project/action. Presently, EPA  in coordination with FHWA and FTA, has provided the following guidance documents  for  assessing CO hot-spot analysis for both project-level air quality requirements under the CAA and  the NEPA:  83  The attainment designations mean that criteria pollutant levels are either below or meet the NAAQS. The  maintenance designation signifies that violations of the NAAQS have occurred in the past but that the area is  currently in attainment.  84  Title 40 CFR Part 93, Subpart A - Conformity to State or Federal Implementation Plans of Transportation  Plans, Programs, and Projects Developed, Funded or Approved Under Title 23 U.S.C. or the Federal Transit  Laws,  http://www.epa.gov/air/genconform/documents/20100324rule.pdf.  85  FHWA and FTA, Title 23 CFR Part 771 –  Environmental Impact and Related Procedures,  Effective: April 23,  2009, http://www.fta.dot.gov/documents/NEPA_reg_clean.pdf.  86  Appendix W to Part 51  – Guideline on Air Quality Models , http://www.ecfr.gov/cgi-bin/text- idx?SID=e6a5b817b94abf58460f48c032d9a39c&node=40:2.0.1.1.2.23.11.5.37&rgn=div9 describes EPA’s  recommended models. Also see EPA’s Technology Transfer Network Support Center for Regulatory  Atmospheric Modeling at http://www.epa.gov/ttn/scram/, EPA’s  MOVES (Motor Vehicle Emission Simulator)  at http://www.epa.gov/otaq/models/moves/, and the  EMFAC model issued by the California Air Resources  Board  at http://www.dot.ca.gov/hq/env/air/pages/emfac.htm.  CO Project-level Analyses  Aviation Emissions and Air Quality Handbook  63$_{ }$