Interim Transportation Conformity 

Guidance for 2006 PM2.5 NAAQS 

Nonattainment Areas
EPA-420-B-09-036

November 2009

Transportation and Regional Programs Division 

Office of Transportation and Air Quality

U.S. Environmental Protection Agency

Interim Transportation Conformity 

Guidance for 2006 PM2.5 NAAQS 

Nonattainment Areas
Table of Contents 

Section 1. Introduction....................................................................................................... 2 

1.1. Purpose of this Guidance .................................................................................... 2 

1.2. Background: Transportation Conformity........................................................... 3 

1.3. 2006 PM2.5 NAAQS and Designations............................................................... 3 

1.4. Relationship Between Transportation Conformity Requirements for the 2006 

PM2.5 NAAQS and the 1997 PM2.5 NAAQS ...................................................... 4 

1.5. Who can I contact for more information?........................................................... 4 

1.6. Does this guidance create any new requirements? ............................................. 5 

Section 2. General Requirements....................................................................................... 6 

2.1. Timing of First Transportation Plan and TIP Conformity Determination.......... 6 

2.2. General Requirements of a Conformity Determination for a Transportation Plan 

and TIP for the 2006 PM2.5 NAAQS .................................................................. 7 

2.3. Consultation for Transportation Plan/TIP Conformity Determinations ............. 8 

2.4. Timely Implementation of TCMs ....................................................................... 9 

2.5. Pollutants and Precursors Examined in the First Regional Emissions Analyses 

for the 2006 PM2.5 NAAQS .............................................................................. 10 

2.6. What happens if an area misses the one-year conformity deadline? ................ 12 

Section 3. Regional Conformity Tests............................................................................. 13 

3.1. Conformity Tests for the First Conformity Determination............................... 13 

3.2. Interim Emissions Tests.................................................................................... 14 

3.3. How should areas determining conformity for PM2.5 for the first time develop 

a regional emissions analysis for an interim emissions test?............................ 15 

3.4. Can an area using an interim emissions test for 1997 PM2.5 conformity apply 

the regional emissions analysis to 2006 PM2.5 conformity as well?................. 16 

3.5. Additional Guidance for 2006 PM2.5 Areas Using the Interim Emissions Tests.. 18 

3.6. Baseline Year for the Baseline Year Test......................................................... 18 

3.7. Using 1997 PM2.5 NAAQS Budgets for 2006 PM2.5 Conformity..................... 19 

3.8. Multi-jurisdictional 2006 PM2.5 Areas That Have 1997 PM2.5 Budgets ......... 20 

Section 4. Project-level Conformity Requirements in 2006 PM2.5 Areas........................ 23 

4.1. Timing of Project-level Conformity Determinations for the 2006 PM2.5

NAAQS............................................................................................................. 23 

4.2. General Requirements....................................................................................... 23 

4.3. What is a hot-spot analysis?.............................................................................. 24 

4.4. Which PM2.5 NAAQS has to be considered in a hot-spot analysis?................. 24 

4.5. Where can I find more information about PM2.5 hot-spot analyses?................ 25 

4.6. Compliance with PM2.5 SIP Control Measures................................................. 25 

1
Section 1. Introduction 

1.1. Purpose of this Guidance 

This document provides interim guidance for meeting transportation conformity 

requirements in areas designated nonattainment for the 2006 24-hour PM2.5 national 

ambient air quality standards (“2006 PM2.5 NAAQS”). EPA published a proposed “PM 

Amendments” rule earlier this year1

 to address the 2006 PM2.5 NAAQS, but the final rule 

has not yet been published. Once the PM Amendments final rule is published, the 

transportation conformity regulations will address the 2006 PM2.5 NAAQS. 

In the interim, EPA is releasing this guidance to help new nonattainment areas meet 

conformity requirements in time. Transportation conformity for the 2006 PM2.5 NAAQS 

applies one year after the effective date of nonattainment designations for this NAAQS. 

Clean Air Act section 176(c)(6) and 40 CFR 93.102(d) provide a one-year grace period 

from the effective date of designations before transportation conformity applies in areas 

newly designated nonattainment for a specific NAAQS. 

EPA’s final rule designating areas for the 2006 PM2.5 NAAQS is effective December 14,

2009. Given this effective date of designations, conformity for this NAAQS applies by 

December 14, 2010. EPA will work with 2006 PM2.5 NAAQS nonattainment areas 

(“2006 PM2.5 areas” in this guidance) to help them meet requirements, and we 

encourage consultation early. 

This is interim guidance and will be replaced by the PM Amendments final rule. 

However, conformity determinations done according to this guidance should be 

consistent with the Clean Air Act and the existing transportation conformity rule, and the 

PM Amendments proposed rule as described in this guidance. Conformity 

determinations for the 2006 PM2.5 NAAQS completed under this interim guidance before 

the PM Amendments final rule becomes effective will remain valid even after the 

effective date of the PM Amendments final rule (i.e., the final rule would not trigger 

another conformity determination for this NAAQS if one has already been completed). 

This guidance document is consistent with what is currently required and being 

implemented for PM2.5 conformity determinations in areas designated for the 1997 PM2.5

NAAQS. 

The Federal Highway Administration (FHWA) and Federal Transit Administration 

(FTA), EPA’s federal partners in implementing the conformity rule, assisted in the 

development of this guidance and concurred on its content. 

 

1

 The proposed rule entitled, “Transportation Conformity Rule PM2.5 and PM10 Amendments,” (“PM 

Amendments”), was published on May 15, 2009.

2
1.2. Background: Transportation Conformity 

Transportation conformity is required under Clean Air Act section 176(c) (42 U.S.C. 

7506(c)) to ensure that federally funded or approved highway and transit activities are 

consistent with (“conform to”) the purpose of the state air quality implementation plan 

(SIP). Conformity to the purpose of the SIP means that transportation activities will not 

cause or contribute to new air quality violations, worsen existing violations, or delay 

timely attainment or any interim milestones of the relevant NAAQS. EPA’s 

transportation conformity rule (40 CFR Parts 51 and 93) establishes the criteria and 

procedures for determining whether metropolitan transportation plans, metropolitan 

transportation improvement programs (TIPs), and federally supported highway and 

transit projects conform to the SIP. Transportation conformity applies to designated 

nonattainment and maintenance areas2 for transportation-related criteria pollutants: 

ozone, PM2.5, PM10, carbon monoxide, and nitrogen dioxide. 

1.3. 2006 PM2.5 NAAQS and Designations 

EPA issued a final rule on October 17, 2006 that tightened the 24-hour PM2.5 NAAQS 

from the 1997 level of 65 micrograms per cubic meter (μg/m3) to 35 μg/m3 (71 FR 

61144). In this final rule, EPA retained the 1997 annual PM2.5 NAAQS of 15.0 μg/m3. 

This final rule was effective on December 18, 2006. EPA selected levels for the final 

NAAQS after completing an extensive review of thousands of scientific studies on the 

impact of fine and coarse particles on public health and welfare. For additional 

information about the October 17, 2006 rulemaking, the final rule and EPA outreach 

materials can be found at: http://www.epa.gov/air/particlepollution/actions.html, under 

the September 21, 2006 announcement. 

EPA’s final rule designating areas for the 2006 PM2.5 NAAQS, published in the Federal 

Register on November 13, 2009, is effective December 14, 2009. 

In this Federal Register notice, EPA has also clarified that all 39 areas designated 

nonattainment for the 1997 PM2.5 NAAQS were violating the annual PM2.5 NAAQS, and 

two of those were also violating the 24-hour PM2.5 NAAQS.3

 That is, EPA’s notice now 

clarifies that only two areas were designated nonattainment for the 1997 24-hour PM2.5

NAAQS, and that all 39 nonattainment areas were designated nonattainment for the 1997 

annual PM2.5 NAAQS. 

 

2

 “Maintenance areas” are those areas that were initially designated nonattainment for a criteria pollutant 

and subsequently redesignated to attainment after 1990. Maintenance areas have SIPs developed under 

Clean Air Act section 175A. 

3

 The two areas designated as nonattainment for both the annual and 24-hour 1997 PM2.5 NAAQS are the 

Los Angeles-South Coast Air Basin, CA nonattainment area and the San Joaquin Valley, CA nonattainment 

area. 

3
Transportation conformity applies for the NAAQS for which an area is designated 

nonattainment.4

 Therefore, in two of the 1997 PM2.5 areas, conformity applies for both 

the 1997 annual and the 1997 24-hour NAAQS.5 In the other 37 1997 PM2.5 areas, 

conformity applies for the 1997 annual NAAQS, and not the 1997 24-hour PM2.5

NAAQS. 

For additional information about the nonattainment designations, refer to EPA’s website 

at: http://www.epa.gov/pmdesignations/2006standards/index.htm. 

1.4. Relationship Between Transportation Conformity Requirements for the 2006 

PM2.5 NAAQS and the 1997 PM2.5 NAAQS 

Clean Air Act section 176(c)(5) requires conformity requirements to be met for the 

applicable PM2.5 NAAQS in both 1997 and 2006 PM2.5 nonattainment and maintenance 

areas. This is because nonattainment designations for the 1997 and 2006 PM2.5 NAAQS 

are different designations with separate SIP requirements, different attainment dates, etc. 

The October 2006 rule establishing the 2006 PM2.5 NAAQS did not revoke the 1997 

annual or 24-hour PM2.5 NAAQS. EPA’s nonattainment designations for the 2006 PM2.5

NAAQS do not affect existing 1997 PM2.5 NAAQS nonattainment designations. While 

making conformity determinations for the 2006 PM2.5 NAAQS will entail additional 

effort, it may be possible to rely on some of the work that has been done to address 

conformity for the 1997 PM2.5 NAAQS, where areas are designated nonattainment for 

both the 1997 and 2006 PM2.5 NAAQS. Refer specifically to Sections 3.4 and 4.4 of this 

guidance for additional information on this point. 

Sections 3 and 4 of this guidance provide information regarding conformity requirements 

for regional emissions analyses and project-level analyses respectively for the 2006 PM2.5

NAAQS. 

1.5. Who can I contact for more information? 

For questions concerning a particular 2006 PM2.5 nonattainment area, please contact the 

transportation conformity staff person responsible for this area at the appropriate EPA 

regional office. Contact information for EPA regional offices can be found on EPA’s 

website at: http://www.epa.gov/otaq/stateresources/transconf/contacts.htm

 

4

 Clean Air Act section 176(c)(5) and 40 CFR 93.102(b). 

5

 These two 1997 PM2.5 areas, the Los Angeles-South Coast Air Basin, CA nonattainment area and the San 

Joaquin Valley, CA nonattainment area have also been designated nonattainment for the 2006 PM2.5

NAAQS. While both the 1997 24-hour and 2006 24-hour PM2.5 NAAQS must be considered in these 

areas, in practice if the more stringent 2006 24-hour PM2.5 NAAQS is met, then the 1997 24-hour PM2.5

NAAQS is met as well. 

4
General questions about this guidance can be directed to Laura Berry at EPA’s Office of 

Transportation and Air Quality, berry.laura@epa.gov, (734) 214-4858. 

The May 15, 2009 PM Amendments proposed rule can be downloaded from EPA’s 

website at: http://www.epa.gov/otaq/stateresources/transconf/conf-regs.htm 

Additional information regarding the transportation conformity rule and associated 

guidance can be found on EPA’s website at: 

www.epa.gov/otaq/stateresources/transconf/index.htm 

Additional information about the 2006 PM2.5 NAAQS nonattainment designations can be 

found on EPA’s website at: 

http://www.epa.gov/pmdesignations/2006standards/index.htm 

1.6. Does this guidance create any new requirements? 

No, this guidance is based on Clean Air Act requirements and existing associated 

regulations and does not create any new requirements. This guidance explains how to 

implement current transportation conformity requirements in areas that have been 

designated for the 2006 PM2.5 NAAQS, prior to EPA’s PM Amendments final rule that 

specifically addresses conformity for this NAAQS. 

The Clean Air Act and EPA’s regulations at 40 CFR Parts 51 and 93 contain legally 

binding requirements. This document is not a substitute for those provisions or 

regulations, nor is it a regulation itself. Thus, it does not impose legally binding 

requirements on EPA, DOT, states, or the regulated community, and may not apply to a 

particular situation based upon the circumstances. This guidance may be revised 

periodically without public notice. 

This guidance will be superseded by EPA’s final rule for the PM Amendments. 

5
Section 2. General Requirements 

2.1. Timing of First Transportation Plan and TIP Conformity Determination 

Transportation conformity for the 2006 PM2.5 NAAQS does not apply until one year after 

the effective date of nonattainment designations for this NAAQS.6

 EPA’s final rule 

designating areas for the 2006 PM2.5 NAAQS is effective December 14, 2009, so 

conformity for this NAAQS applies December 14, 2010. 

The following discussion provides more details on the application of the one-year grace 

period in newly designated nonattainment areas for the 2006 PM2.5 NAAQS in 

metropolitan, donut and isolated rural areas. This information is consistent with how 

conformity for new NAAQS has been implemented in the past.7

 Also see Section III.B. 

of the preamble of the PM Amendments proposed rule (74 FR 23026-23028). 

A metropolitan planning organization (MPO) 8 and the U.S. Department of 

Transportation (DOT) must make a conformity determination with regard to the 2006 

PM2.5 NAAQS for the metropolitan transportation plan and TIP within one year after the 

effective date of the initial nonattainment designation for this NAAQS. The MPO and 

DOT can make such a conformity determination anytime during the one-year grace 

period, as long as it is completed by December 14, 2010. However, if the MPO and DOT 

miss the deadline, the nonattainment area would enter a conformity “lapse.” See Section 

2.8 below for more information on lapses. 

Conformity determinations done by an MPO (or MPOs) must also include any donut 

areas9 within the 2006 PM2.5 NAAQS area (40 CFR 93.102(b)(2) and 93.122(a)(1)). 

MPOs must continue to meet conformity requirements for any other applicable NAAQS, 

including the 1997 PM2.5 NAAQS, if the area is designated nonattainment or 

maintenance for such NAAQS as well. Determining conformity for these other NAAQS 

during the one-year grace period is not necessary unless required by 40 CFR 93.104 (for 

example, a new or amended transportation plan and TIP are to be adopted). The 

procedures for the interagency consultation process found in 40 CFR 93.105 or a state’s 

 

6

 Clean Air Act section 176(c)(6) and 40 CFR 93.102(d) provide a one-year grace period from the effective 

date of designations before transportation conformity applies in areas newly designated nonattainment for a 

particular NAAQS. 

7

 For example, the one-year grace period for newly designated areas was discussed in the July 1, 2004 final 

rule, 69 FR 40008 – 40009. 

8

 Metropolitan areas are urbanized areas that have a population greater than 50,000 and a designated 

metropolitan planning organization (MPO) responsible for transportation planning per 23 U.S.C. 134. See 

40 CFR 93.101 for the definition of metropolitan planning organization. 

9

 A donut area is defined in 40 CFR 93.101 as a geographic area outside a metropolitan planning area 

boundary, but inside a designated nonattainment or maintenance area boundary that includes an MPO. 

6
approved conformity SIP must be used in making conformity determinations for 

transportation plans and TIPs. 

The interagency consultation group for each newly designated nonattainment area that 

includes a donut portion should determine how best to consider the donut area 

transportation system and new donut area projects in the MPO’s regional emissions 

analyses and transportation plan and TIP conformity determinations. For more 

discussion on how conformity determinations should be made for donut areas, see the 

preamble to the July 1, 2004 conformity rule (69 FR 40013). 

In isolated rural areas,10 as in other newly designated nonattainment areas, the one-year 

conformity grace period for the 2006 PM2.5 NAAQS will begin on the effective date of an 

isolated rural area’s initial nonattainment designation. However, because these areas do 

not have federally required metropolitan transportation plans and TIPs, they are not 

subject to the frequency requirements for conformity determinations on transportation 

plans and TIPs (40 CFR 93.104(b), (c), and (e)). Instead, in an isolated rural area, a 

conformity determination is required for the 2006 PM2.5 and other applicable NAAQS 

only when a non-exempt FHWA/FTA project(s) needs funding or approval. Conformity 

requirements for isolated rural areas can be found at 40 CFR 93.109(l). 

See EPA’s July 1, 2004 final rule for further background on how EPA has implemented 

this conformity grace period for 1997 PM2.5 NAAQS areas (69 FR 40004). 

2.2. Overview of Requirements of a Conformity Determination for a Transportation 

Plan and TIP for the 2006 PM2.5 NAAQS 

For all areas where conformity applies, including the 2006 PM2.5 areas, Table 1 found in 

40 CFR 93.109(b) lists the conformity criteria that apply for transportation plans, TIPs, 

and projects. See Section 4 of this guidance for information about conformity 

determinations for federally funded or approved projects. 

A transportation plan or TIP conformity determination must include a regional emissions 

analysis that meets the requirements of 40 CFR 93.122. This regional emissions analysis 

must: 

 use latest planning assumptions (40 CFR 93.110); 

 use the latest emissions model (40 CFR 93.111);11 

 

10 Isolated rural nonattainment and maintenance areas are defined in 40 CFR 93.101 as areas that do not 

contain or are not part of any metropolitan planning area as designated under the transportation planning 

regulations. Refer to 40 CFR 93.101 for additional information. 

11 The latest emissions model is currently MOBILE6.2 for all states except California, and EMFAC2007 

for California. While EPA will soon be issuing the final MOVES model to replace MOBILE6.2 (a draft 

version of MOVES has already been released and can be downloaded from EPA’s website at 

http://www.epa.gov/otaq/models/moves/index.htm), EPA will establish a grace period before MOVES is 

required, according to 40 CFR 93.111(b). Therefore, implementers will be able to use MOBILE6.2 for the 

first 2006 PM2.5 NAAQS conformity determination if the regional emissions analysis is started before the 

7
 pass the appropriate conformity test – the budget test and/or one of the interim 

emissions tests – as described in Section 3 of this guidance. 

In addition, other requirements must be met and documented in the transportation plan 

and TIP conformity determination: 

 Interagency consultation and public participation (40 CFR 93.112) – see Section 

2.3 of this guidance; 

 Timely implementation of transportation control measures (TCMs) in approved 

SIPs (40 CFR 93.113) – see Section 2.4 of this guidance. 

 

Please refer to the sections of the transportation conformity regulation noted above for 

additional information that is not covered in this interim guidance. 

2.3. Consultation for Transportation Plan/TIP Conformity Determinations 

Interagency Consultation. Conformity must be determined in consultation with the 

appropriate local, state, and federal agencies based on the requirements of 40 CFR 

93.112. If your state has an approved conformity SIP, consultation must meet the 

requirements found in that SIP. 12 If your state does not have such an approved 

conformity SIP, consultation must meet the requirements found in 40 CFR 93.105(a)(2). 

When making a conformity determination, 2006 PM2.5 areas must use the interagency 

consultation process to make decisions regarding specific aspects of the conformity 

determination. For example, consultation must be used to: 

 Determine the model, methods, and assumptions to be used in regional emissions 

analyses and hot-spot analyses13 (40 CFR 93.105(c)(1)(i)) – see footnote 11 

regarding the emissions model to be used; 

 Determine whether there are any transportation projects in the area that don’t fit 

the definition of “regionally significant project” found in 40 CFR 93.101 but 

should be included in the area’s regional emissions analysis (40 CFR 

93.105(c)(1)(ii)); 

 end of the grace period for MOVES. See EPA’s website at: 

http://www.epa.gov/otaq/stateresources/transconf/policy.htm for upcoming MOVES SIP and conformity 

policy guidance that will describe how MOVES will be applied in these areas. 

 

12 A conformity SIP governs the conformity process in a state for the portions of the federal transportation 

conformity regulations that it includes. A conformity SIP is required to contain only the state’s criteria and 

procedures for interagency consultation (40 CFR 93.105) and two additional conformity provisions (40 

CFR 93.122(a)(4)(ii) and 93.125(c)). Unlike a reasonable further progress SIP, an attainment 

demonstration, or maintenance plan, a conformity SIP does not contain motor vehicle emissions budgets, 

emissions inventories, air quality demonstrations, or control measures. For more information, see EPA’s 

“Guidance for Developing Transportation Conformity State Implementation Plans (SIPs),” found on EPA’s 

website at: http://www.epa.gov/otaq/stateresources/transconf/policy/420b09001.pdf . 

13 This includes making specific decisions such as the time of year that should be modeled, as appropriate, 

which years should be analyzed, and models and inputs to be used. 

8
 Evaluate whether the area has any projects that are exempt according to 40 CFR 

93.126 and 93.127 that should be treated as non-exempt (40 CFR 

93.105(c)(1)(iii)); 

 Determine whether there are any TCMs in an approved SIP for the area and 

evaluate whether those TCMs are behind schedule. For any TCM behind 

schedule, determine whether past obstacles to its implementation have been 

identified and are being overcome, and whether the TCM is getting maximum 

priority for approval and funding (40 CFR 93.105(c)(1)(iv)). See Section 2.4 of 

this guidance for more information on this requirement. 

Note that this is a partial list of items to be discussed through the interagency consultation 

process; see the state’s conformity SIP or the transportation conformity rule at 40 CFR 

93.105(c) for the complete list. 

Those 2006 PM2.5 areas where conformity already applies for another NAAQS will be 

able to use their existing interagency consultation process for making these decisions. 

These areas should consider whether any additional agencies need to be part of the 

process if the boundary of the 2006 PM2.5 area is different from the area where 

conformity already applies. 

Public Consultation. Agencies making conformity determinations must also give the 

public an opportunity for comment, in accordance with the rule’s requirements at 40 CFR 

93.105(e) or any state’s approved conformity SIP. Note that the public must have access 

to all technical and policy information considered by the agency making the conformity 

determination at the beginning of the comment period, and prior to taking formal action 

on the conformity determination. The requirements of a proactive public involvement 

process are outlined in DOT’s transportation planning regulations at 23 CFR 450.316(a). 

2.4. Timely Implementation of TCMs 

The conformity determination must include a demonstration of timely implementation of 

TCMs in approved SIPs as required by 40 CFR 93.113(b) for transportation plans and 40 

CFR 93.113(c) for TIPs. The conformity rule defines transportation control measures at 

40 CFR 93.101. The requirements for timely implementation of TCMs apply only to 

TCMs in an approved SIP. Most likely, 2006 PM2.5 areas will not have an approved SIP 

for this NAAQS during the time that this guidance is in effect. 

However, these areas could have approved SIPs for the 1997 PM2.5 NAAQS or another 

NAAQS. Conformity determinations for the 2006 PM2.5 NAAQS must ensure timely 

implementation of any TCMs included in any approved SIPs for the area.14 EPA 

addressed this point in the July 1, 2004 final rule: 

 

14 If a TCM in an approved SIP has already been substituted with one or more other TCMs, the timely 

implementation requirement applies to the substitute TCM(s). For additional information about 

substituting TCMs, please refer to EPA’s “Guidance for Implementing the Clean Air Act Section 176(c)(8) 

9
Clean Air Act section 176(c) requires that TCMs in approved SIPs be 

implemented in a timely manner according to the schedules in the SIP. 

This requirement is not contingent on what type of SIP, pollutant, or 

standard for which the approved TCM was established. (69 FR 40013).

2.5. Pollutants and Precursors Examined in the First Regional Emissions Analyses 

for the 2006 PM2.5 NAAQS

The transportation conformity rule at 40 CFR 93.102(b) describes the pollutants that must 

be examined in a regional emissions analysis done for PM2.5: 

Directly emitted PM2.5. In 2006 PM2.5 areas, regional conformity analyses must be 

completed for directly emitted PM2.5 (40 CFR 93.102(b)(1)). Directly emitted PM2.5

includes exhaust, brake and tire wear emissions,15 and re-entrained road dust may also 

have to be included as directly emitted PM2.5 as discussed below. 

Oxides of nitrogen (NOx). Regional conformity analyses must be completed for NOx in 

2006 PM2.5 areas, unless both the EPA Regional Administrator and the director of the 

state air agency make a finding that transportation-related emissions of NOx within the 

nonattainment area are not a significant contributor to the PM2.5 nonattainment problem 

and notify the MPO and DOT (40 CFR 93.102(b)(2)(iv)). 

Other potential precursors. Regional conformity analyses are not required for volatile 

organic compounds (VOC), sulfur dioxide (SO2) or ammonia (NH3) in 2006 PM2.5 areas 

unless either the EPA Regional Administrator or the director of the state air agency 

makes a finding that transportation-related emissions of any of these precursors within 

the nonattainment area are a significant contributor to the PM2.5 nonattainment problem 

and notifies the MPO and DOT (40 CFR 93.102(b)(2)(v)). 

Areas should use the interagency consultation process if there are questions about 

whether conformity applies for a PM2.5 precursor. 

Re-entrained road dust.

Re-entrained road dust emissions are produced by travel on paved and unpaved roads, 

including emissions from anti-skid and de-icing materials. Re-entrained road dust isn’t

included in the regional emissions analysis for direct PM2.5 unless either the EPA 

Regional Administrator or the director of the state air agency makes a finding that reentrained road dust emissions within the area are a significant contributor to the PM2.5

nonattainment problem and notifies the MPO and DOT (40 CFR 93.102(b)(3)). 

 Transportation Control Measure Substitution and Addition Provision,” found on EPA’s website at: 

http://www.epa.gov/otaq/stateresources/transconf/policy/420b09002.pdf . 

15 The latest approved emissions model is used to estimate directly emitted PM2.5 from vehicle exhaust and 

brake and tire wear – MOBILE6.2 in all states other than California, and EMFAC2007 in California. 

10
The interagency consultation process must be used to discuss what modeling methods 

and data are appropriate for a conformity analysis, per 40 CFR 93.105(c)(1). Areas are 

required to use AP-4216 to estimate road dust unless they have an EPA-approved local 

method. 

Construction dust. 

Most areas will not need to be concerned about including construction-related fugitive 

dust in a regional emissions analysis during the time that this interim guidance applies. 

Construction-related fugitive dust needs to be included in a 2006 PM2.5 regional 

emissions analysis only if the SIP identifies it as a significant contributor to the PM2.5

nonattainment problem, based on 40 CFR 93.122(f). In such a case, the regional PM2.5

emissions analysis has to consider construction-related fugitive PM2.5 and account for the 

level of construction activity, the fugitive PM2.5 control measures in the SIP, and the dustproducing capacity of the proposed activities (40 CFR 93.122(f)(2)). 

The interagency consultation process must be used to discuss what methods and data are 

appropriate for estimating construction dust emissions (40 CFR 93.105(c)(1)(i)). Either 

AP-42 or locally-developed methods could be used, as determined through consultation. 

 

 

16 See the Notice of Availability published May 19, 2004, (69 FR 28830-28832) found on EPA’s website 

at: http://www.epa.gov/fedrgstr/EPA-AIR/2004/May/Day-19/a11340.htm and more recently, EPA’s 

memorandum, “Policy Guidance on the Use of the November 1, 2006, Update to AP-42 for Re-entrained 

Road Dust for SIP Development and Transportation Conformity,” August 2, 2007, found on EPA’s website 

at: http://www.epa.gov/otaq/stateresources/transconf/policy/420b07055.pdf . 

11
The following table summarizes the information in Section 2.5: 

Pollutants Examined for PM2.5 Regional Emissions Analysis:17

Pollutant/Precursor Included in 2006 PM2.5 Regional 

Emissions Analysis? 

Direct PM2.5 – exhaust, brake and tire wear Yes 

NOx Yes, 

unless both EPA and the state find that it is 

not a significant contributor 

VOCs, SO2, or NH3 No, 

unless either EPA or the state finds any of 

these precursors are a significant 

contributor (or SIP includes a budget for 

any of these precursor) 

Re-entrained road dust No, 

unless either EPA or the state finds it a 

significant contributor (or included in SIP 

budget) 

Construction dust No, 

unless SIP identifies it as a significant 

contributor 

2.6. What happens if an area misses the one-year conformity deadline? 

If, at the conclusion of the one-year grace period for newly designated areas, the MPO 

and DOT have not made a transportation plan and TIP conformity determination for the 

relevant pollutant and NAAQS, the area would be in a conformity “lapse.” During a 

conformity lapse, only certain projects can receive additional federal funding or 

approvals to proceed (e.g. exempt projects, project phases that were approved before the 

lapse). The practical impact of a conformity lapse will vary on an area-by-area basis. 

The lapse grace period found in 40 CFR 93.104(b)(3) and (c)(3) does not apply at the end 

of the one-year conformity grace period for newly designated areas. 

Although the one-year conformity grace period is available to isolated rural areas, most 

likely no conformity consequences would occur. As discussed in Section 2.1 of this 

guidance, a conformity determination is required in isolated rural areas only when a nonexempt FHWA/FTA project needs funding or approval. 

Section III.B. of the preamble of the PM Amendments proposed rule (74 FR 23026-

23028) also covers this information. 

 

17 Information in the table is based on 40 CFR 93.102(b)(2) and (3). 

12
Section 3. Regional Conformity Tests 

The conformity rule provides several tests for determining whether transportation plans 

and TIPs conform, and 40 CFR 93.109 indicates which test or tests are required in 

specific circumstances. The budget test, described at 40 CFR 93.118, is used when an 

area has either adequate or approved motor vehicle emissions budgets in a SIP. The 

interim emissions tests are found at 40 CFR 93.119. When a 2006 PM2.5 area does not 

have adequate or approved PM2.5 budgets for any PM2.5 NAAQS, one of the two interim 

emissions tests must be done, as described below. 

3.1. Conformity Tests for the First Conformity Determination 

For the first conformity determination for the 2006 PM2.5 NAAQS, SIP budgets for this 

NAAQS will not yet be submitted. Therefore, these areas will have to use a different test 

for conformity: 

 If a 2006 PM2.5 area has adequate or approved SIP budgets from a SIP that 

addresses the 1997 PM2.5 NAAQS, it must use the budget test for 2006 PM2.5

conformity18 (skip to Section 3.7); 

 If a 2006 PM2.5 area does not have adequate or approved budgets for the 1997 

PM2.5 NAAQS, it must use one of the interim emissions tests, either: 

o the build-no-greater-than-no-build test (“build/no-build test”) found at 40 CFR 

93.119(e)(1), or 

o the no-greater-than-baseline year emissions test (“baseline year test”), 

described at 40 CFR 93.119(e)(2). 

The information discussed here is consistent with the PM Amendments proposed rule; 

see preamble Sections V and VI, and proposed regulatory text in §93.109(j) and (k) as 

background. 

The interagency consultation process must be used to determine which test for 

conformity applies, and other details as described in Section 2.3 of this guidance. 

Additional decisions will need to be made through interagency consultation if the area 

covers multiple jurisdictions, for example, if the area includes portions of more than one 

state, or is covered by more than one MPO. 

 

18 At this time it is known that all but three areas that are designated for both the 2006 and 1997 PM2.5

NAAQS have 2006 PM2.5 nonattainment boundaries that cover exactly the same geographic area as the 

1997 PM2.5 boundaries. In two areas the 2006 PM2.5 boundary is smaller than the 1997 PM2.5 boundary, 

and one 2006 PM2.5 area is comprised of two 1997 PM2.5 areas. Therefore, in nearly all cases if 1997 PM2.5

budgets are available, meeting the budget test will be sufficient because it will cover the entire 2006 PM2.5

area. EPA will work with all areas to ensure they know which type of test applies for conformity. 

13
Where an area is also subject to conformity for the 1997 PM2.5 NAAQS, some of the 

work done for the 1997 PM2.5 NAAQS conformity determination may be useful for the 

2006 PM2.5 conformity determination. Refer to Section 3.4 of this guidance. 

EPA will work DOT and state and local transportation and air quality agencies to 

determine which conformity test applies in each 2006 PM2.5 area for the first 

determination. 

3.2. Interim Emissions Tests 

As mentioned in Section 3.1. above, areas that do not have adequate or approved PM2.5

budgets for any PM2.5 NAAQS must use one of the interim emissions tests according to 

the regulations at 40 CFR 93.119(e). As described in Section V of the PM Amendments 

proposed rule preamble, the 2006 PM2.5 areas that must use one of the interim emissions 

tests are either: 

 “Brand new” PM2.5 nonattainment areas, i.e., those that were designated 

attainment for the 1997 PM2.5 NAAQS, or 

 Areas that were designated nonattainment for the 1997 PM2.5 NAAQS that do not 

yet have adequate or approved budgets for the 1997 PM2.5 NAAQS. 

These 2006 PM2.5 nonattainment areas have a choice between the following interim 

emissions tests in 40 CFR 93.119 for conformity determinations conducted before 

adequate or approved 2006 PM2.5 SIP budgets are established: 

 The build-no-greater-than-no-build test (“build/no-build test”) found at 40 CFR 

93.119(e)(1). In this test, conformity would be demonstrated if in each analysis 

year, the transportation emissions reflecting the proposed transportation plan or 

TIP (the “build” case) were less than or equal to emissions from the transportation 

system that would result from current programs (the “baseline scenario” or “nobuild” case defined in 40 CFR 93.119(h)); OR 

 The no-greater-than-baseline year emissions test (“baseline year test”), described 

at 40 CFR 93.119(e)(2). In this test, conformity would be demonstrated if in each 

analysis year, the transportation emissions reflecting the proposed transportation 

plan or TIP (the “build” case) were less than or equal to the level of motor vehicle 

emissions in the baseline year. Refer to Section 3.6 of this guidance for a 

discussion of baseline years. 

These requirements are also discussed in Section V of the preamble of the PM 

Amendments proposed rule. 

Regardless of whether the area chooses the baseline year test or build/no-build test, the 

required analysis years, based on 40 CFR 93.119(g), are: 

14
 A year within five years of the date the analysis is being done; 

 The last year of the transportation plan / conformity determination; and 

 Intermediate years as necessary so that analysis years are not more than 10 years 

apart. 

Please refer to the transportation conformity rule for further explanation of these tests. 

Note that those 2006 PM2.5 areas that contain more than one MPO and/or a donut portion 

would follow EPA’s existing 2004 guidance entitled, “Companion Guidance for the July 

1, 2004 Final Transportation Conformity Rule, Conformity Implementation in MultiJurisdictional Nonattainment and Maintenance Areas for Existing and New Air Quality 

Standards,” (EPA420-B-04-012), (the “multi-jurisdictional guidance”). See Section 3.5 

of this guidance for more information about the multi-jurisdictional guidance. 

3.3. How should areas determining conformity for PM2.5 for the first time develop a 

regional emissions analysis for an interim emissions test? 

Because the 2006 PM2.5 NAAQS designations were only for the 2006 24-hour PM2.5

NAAQS, the regional emissions analysis will be based on emissions for a 24-hour time 

period. 

For either the baseline year test or the build/no-build test, for each analysis year, 

emissions must be estimated for the build scenario according to 40 CFR 93.119(i) with a 

24-hour emissions inventory. (The build scenario is referred to as the “Action” scenario 

at 40 CFR 93.119(i).) 

This 24-hour emissions inventory estimates direct PM2.5 and NOx emissions that result 

from the build scenario using MOBILE6.2 in a 24-hour period. For each analysis year 

chosen, areas should choose MOBILE6.2 inputs for the season of the year where 

violations of the 2006 PM2.5 NAAQS occurred.19 If violations occurred in more than one 

season, implementers should use the interagency consultation process to choose the 

season (or seasons) that would best ensure that the Clean Air Act is met, for example by 

choosing the season with the most frequent or most severe violations, or the season with 

the highest VMT, or both.20 The choice of season or seasons should be based on air 

quality data from the three years used to make designations (i.e., 2006 – 2008). 

Interagency consultation should be used to decide if more recent air quality data indicates 

that a different season should be analyzed. 

 

19 In California where EMFAC is used, areas should use the interagency consultation process to determine 

appropriate methods. 

20 Note that this guidance regarding the choice of season applies only when using MOBILE6.2 and not 

MOVES because MOBILE6.2 PM2.5 emission factors are not sensitive to changes in temperature. EPA 

will provide guidance on this issue when MOVES is released. See EPA’s website at: 

http://www.epa.gov/otaq/models/moves/index.htm and 

http://www.epa.gov/otaq/stateresources/transconf/policy.htm for future MOVES guidance. 

15
For each analysis year, these emission factors from MOBILE6.2 for direct PM2.5 and 

NOx for the season chosen should be multiplied by the seasonally-adjusted average daily 

VMT in that analysis year to create an estimate of transportation emissions in a 24-hour 

period. For additional guidance on creating daily emissions inventories, refer to EPA’s 

existing guidance documents.21 

Note that whatever season is chosen to estimate the build scenario emissions, the same 

season should be used for comparison whether using the baseline year test or build/nobuild test. For example, emissions for a build scenario calculated using winter 

MOBILE6.2 inputs should be compared to emissions in the winter of the baseline year 

(see Section 3.6. for a discussion of the baseline year in 2006 PM2.5 areas), or emissions 

in winter from the no-build scenario. 

Refer to 40 CFR 93.119 for addition information about conducting the build/no-build and 

baseline year tests. 

3.4. Can an area using an interim emissions test for 1997 PM2.5 conformity apply 

the regional emissions analysis to 2006 PM2.5 conformity as well? 

When areas are determining conformity for the 1997 and 2006 PM2.5 NAAQS at the same 

time, they could apply some of the information developed in the 1997 PM2.5 regional 

emissions analysis in creating a 2006 PM2.5 regional emissions analysis. 

First, note that regardless of whether the area is using the baseline year test or build/nobuild test, the same analysis years can be used for 1997 PM2.5 conformity and 2006 PM2.5

conformity when the analyses are done at the same time, if they meet applicable 

requirements for both NAAQS (refer to Section 3.2 of this guidance and 40 CFR 

93.119(g) for analysis year requirements). 

In most 1997 PM2.5 areas, conformity applies only for the annual NAAQS.22 While the 

results of an interim emissions test for the 1997 annual PM2.5 NAAQS cannot be directly 

applied for the 2006 24-hour PM2.5 NAAQS, the option described below could save 

implementers some effort when conformity is being determined for both of these 

 

21 Specifically, see EPA’s “Technical Guidance on the Use of MOBILE6.2 for Emission Inventory 

Preparation,” EPA420-R-04-013, August 2004, found on EPA’s website at: 

http://www.epa.gov/otaq/models/mobile6/420r04013.pdf and “Procedures for Emission Inventory 

Preparation - Vol IV: Mobile Sources,” found at: http://ntl.bts.gov/DOCS/AQP.html

22 See Section 1.3 of this guidance. In two of the 1997 PM2.5 areas, conformity applies for both the 1997 

annual PM2.5 NAAQS and the 1997 24-hour PM2.5 NAAQS. However, note that Section 3.4 of this 

guidance would not apply to these two areas if they have adequate 1997 PM2.5 SIP budgets. 

16
NAAQS at the same time. This option applies only when using MOBILE6.2 for regional 

emissions analyses.23 

Areas should develop the annual emissions for the 1997 PM2.5 NAAQS by estimating 

emissions in two seasons, summer and winter; four seasons; or in the 12 months of the 

year.24 

To apply information from the analysis done for the 1997 PM2.5 NAAQS to the 2006 

PM2.5 analysis, for each analysis year, areas should use the emission factors developed in 

the 1997 PM2.5 NAAQS regional emissions analysis for PM2.5 and NOx in a season or 

month where violations of the 2006 PM2.5 NAAQS occurred, and multiply these emission 

factors by the seasonally-adjusted average daily VMT for the area of the analysis year.25 

If violations occurred in more than one season or month, the interagency consultation 

process should be used to choose the season or month that would best ensure that the 

Clean Air Act is met, for example by choosing the season with the most frequent or most 

severe violations, or the season with the highest VMT, or both.26 The choice of season 

or seasons should be based on air quality data from the three years used to make 

designations (i.e., 2006 – 2008), unless more recent air quality data indicates that a 

different season should be analyzed, as decided through consultation. 

Whatever season is chosen to estimate the build scenario emissions, the same season 

should be used for comparison whether using the baseline year test or build/no-build test. 

For example, emissions for a build scenario calculated using winter MOBILE6.2 inputs 

should be compared to emissions in the winter of the baseline year (see Section 3.6. for a 

discussion of the baseline year in 2006 PM2.5 areas), or emissions in winter from the nobuild scenario. 

Note that prior to the effective date of the PM Amendments final rule, the baseline year 

for the 1997 and 2006 PM2.5 NAAQS will be the same year – 2002. After the effective 

 

23 Areas in California should use the interagency consultation process to determine appropriate methods. In 

all other 2006 PM2.5 areas, EPA expects that MOBILE6.2 will be used for the first 2006 PM2.5 conformity 

determinations. Refer to footnote 11 for more information about the use of MOBILE6.2. 

24 This interim guidance for 2006 PM2.5 areas does not change how analyses are to be done for the 1997 

PM2.5 NAAQS, which is covered in “Guidance for Creating Annual On-Road Mobile Source Emission 

Inventories for PM2.5 Nonattainment Areas for Use in SIPs and Conformity,” EPA420-B-05-008, August 

2005, found on EPA’s website at: 

http://www.epa.gov/otaq/stateresources/transconf/policy/420b05008.pdf. In particular, Question 7 on pp. 

5-8 of that guidance addresses how analyses are to be done for the 1997 PM2.5 NAAQS. 

25 If a 24-hour emissions estimate is available in the appropriate season or month because this step has been 

completed for 1997 PM2.5 NAAQS conformity and conformity is being determined for the 1997 PM2.5

NAAQS and the 2006 PM2.5 NAAQS at the same time, it does not need to be redone but can be applied in 

the regional emissions analysis for 2006 PM2.5 conformity. 

26 Note that this guidance regarding the choice of season applies only when using MOBILE6.2 and not 

MOVES because MOBILE6.2 PM2.5 emission factors are not sensitive to changes in temperature. EPA’s 

MOVES guidance documents will differ from this interim guidance in this respect. 

17
date of the final rule, EPA has proposed in the PM Amendments proposed rule that the 

baseline year for the 2006 PM2.5 NAAQS would be a different year. See Section 3.6 of 

this guidance for additional discussion of the baseline year. 

3.5. Additional Guidance for 2006 PM2.5 Areas Using the Interim Emissions Tests 

Any areas that use one of the interim emissions tests may also want to refer to Part 2 of 

EPA’s multi-jurisdictional guidance.27 Part 2 of the multi-jurisdictional guidance covers 

conformity determinations and regional emissions analyses before SIP budgets are 

adequate or approved, and specifically addresses the following topics: 

 The geographic area to be examined in a regional emissions analysis and 

conformity determination before the area has adequate or approved budgets 

(Question 3, p. 8 of multi-jurisdictional guidance); 

 How multi-jurisdictional areas can create a regional emissions analysis for the 

entire nonattainment area (Question 4, p. 9 of multi-jurisdictional guidance); 

 The decisions to be made in the interagency consultation process (Question 5, p. 

11 of the multi-jurisdictional guidance); 

 What occurs when one MPO can meet the requirements in 40 CFR 93.119 and the 

other cannot (Question 6, p. 12 of the multi-jurisdictional guidance); and 

 Who has responsibility for estimating emissions in a donut area (Question 7, p. 13 

of the multi-jurisdictional guidance). 

3.6. Baseline Year for the Baseline Year Test 

The required baseline year for the 2006 PM2.5 NAAQS may change once the PM 

Amendments final rule is published and effective. Prior to the effective date of the final 

rule, the baseline year for these areas is 2002 (found in 40 CFR 93.119(e)). However, 

EPA has proposed to update the baseline year for 2006 PM2.5 areas, which if finalized, 

would result in baseline years of either 2005 or 2008. 

Any conformity determination finished28 before the PM Amendments final rule becomes 

effective must use 2002 as the baseline year. Such a determination will remain valid 

even after the effective date of the PM Amendments final rule, which may specify a 

different baseline year for 2006 PM2.5 areas. Any conformity determination finished after 

the effective date of the PM Amendments final rule must use the baseline year identified 

in the final rule. (EPA proposed that only one of the options would be finalized, therefore 

 

27 “Companion Guidance for the July 1, 2004, Final Transportation Conformity Rule: Conformity 

Implementation in Multi-jurisdictional Nonattainment and Maintenance Areas for Existing and New Air 

Quality Standards,” EPA420-B-04-012, July 2004, found on EPA’s website at 

http://www.epa.gov/otaq/stateresources/transconf/policy/420b04012.pdf . 

28 A conformity determination is finished on the date that DOT makes its conformity determination. 

18
only one of the two years identified above – either 2005 or 2008 – would be the resulting 

baseline year). 

EPA recommends that MPOs use the interagency consultation process to discuss the 

likely timing of DOT’s conformity determination, and which baseline year will most 

likely be in effect at that time. EPA Regional Offices are available for consultation on a 

case-by-case basis; refer to Section 1.5 for contact information. 

MPOs using the baseline year test could also compare emissions from the future planned 

transportation network to emissions in 2002, 2005, and 2008, since those are the baseline 

years that would result from the options EPA set forth in the PM Amendments proposed 

rule. However, EPA believes that the consultation process can help MPOs avoid this 

additional work. 

Note that the baseline year emissions need to be modeled rather than interpolated, based 

on the latest emissions model and appropriate methods for estimating travel and speeds as 

required by 40 CFR 93.110, 93.111, and 93.122. 

3.7. Using 1997 PM2.5 NAAQS Budgets for 2006 PM2.5 Conformity 

As discussed in preamble Section IV of the PM Amendments proposed rule, where a 

2006 PM2.5 area is covered by adequate or approved 1997 PM2.5 budgets, EPA believes 

that the 1997 PM2.5 budgets must be used for 2006 PM2.5 conformity. Most of the areas 

designated for both the 2006 and 1997 PM2.5 NAAQS have 2006 PM2.5 nonattainment 

boundaries that cover exactly the same geographic area as the 1997 PM2.5 boundaries. 

Therefore, in most cases if 1997 PM2.5 budgets are available, meeting the budget test will 

be sufficient because it will cover the entire 2006 PM2.5 area.29 Consistent with the Clean 

Air Act as interpreted by a court decision described below, these areas must meet the 

budget test for the 2006 PM2.5 NAAQS using existing adequate or approved SIP budgets 

for the 1997 PM2.5 NAAQS. 

For areas that use 1997 annual PM2.5 budgets to meet 2006 PM2.5 requirements, a 

regional emissions analysis for the 2006 PM2.5 NAAQS would necessarily be done based 

on an analysis of annual emissions (tons per year), rather than 24-hour emissions (tons 

per day). 

This requirement to use adequate or approved 1997 PM2.5 budgets is based on EPA’s 

existing rule for areas designated for the 1997 8-hour ozone NAAQS that had SIP 

budgets for the 1-hour ozone NAAQS and a 2006 court decision. EPA has proposed in 

the PM Amendments proposed rule to add a regulatory provision to clarify this 

requirement. Thus, EPA believes that using the existing 1997 PM2.5 budgets as a proxy 

 

29 At this time, it is known that in two areas the 2006 PM2.5 boundary is smaller than the 1997 PM2.5

boundary, and that one 2006 PM2.5 area comprised of two 1997 PM2.5 areas. EPA will work with all areas 

to ensure they know which type of test applies for conformity, particularly with the areas where the 2006 

PM2.5 area boundary is not identical to the 1997 PM2.5 area boundary. 

19
for the 2006 PM2.5 NAAQS is required by the Clean Air Act. In Environmental Defense 

v. EPA, 467 F.3d 1329 (D.C. Cir. 2006), the Court of Appeals for the District of 

Columbia Circuit held that in contrast to the provisions of EPA’s rules under review, 

where a motor vehicle emissions budget developed for the revoked 1-hour ozone 

NAAQS existed in an approved SIP, the Act requires that that budget must be used to 

demonstrate conformity to the 8-hour ozone NAAQS until the SIP is revised to include 

budgets for the new NAAQS. EPA reflected the court’s decision for ozone conformity 

tests in its January 24, 2008 final rule (73 FR 4434). While the Environmental Defense 

case concerned ozone, EPA believes the court’s holding is relevant for other pollutants 

for which conformity must be demonstrated. Consequently, EPA believes that 2006 

PM2.5 areas that have 1997 PM2.5 budgets must use them for 2006 PM2.5 conformity 

before 2006 PM2.5 SIP budgets are established. See Section VI of the preamble of the 

PM Amendments proposed rule (74 FR 23032 – 23035), and the proposed regulatory text 

in §93.109(k). 

The 2006 PM2.5 areas with adequate or approved 1997 PM2.5 budgets can determine 

conformity for both of these NAAQS at the same time. When using the budget test, the 

regional emissions analysis must be performed for: 

 The attainment year for the applicable NAAQS, if it is in the timeframe of the 

transportation plan and conformity determination; 

 The last year of the transportation plan/conformity determination; and 

 Intermediate years as necessary such that analysis years are no more than ten 

years apart (40 CFR 93.118(d)). 

Note that the analysis years chosen must meet 40 CFR 93.118(d) for each NAAQS. The 

last year of the transportation plan will be the same regardless of NAAQS, but the 

attainment years for the two NAAQS will be different. Based on Clean Air Act section 

172(a)(2), the attainment year for the 2006 PM2.5 areas will be 2014, five years after the 

effective date of designations, (December 13, 2009).30 

For areas where 1997 PM2.5 subarea budgets are established, or where 1997 PM2.5

budgets are established for individual states in a multi-state area, the 2004 multijurisdictional guidance addresses how conformity is done. See Section 3.8 for more 

information. This information is also discussed in the PM Amendments proposed rule at 

74 FR 23032 – 23035. 

3.8. Multi-jurisdictional 2006 PM2.5 Areas That Have 1997 PM2.5 Budgets 

In 2006 PM2.5 areas that include more than one MPO, an MPO and a donut area, or more 

than one state, the multi-jurisdictional guidance referenced above provides relevant 

guidance for preparing conformity determinations. The most relevant information from 

the multi-jurisdictional guidance has been adapted and included here for 2006 PM2.5

 

30 Areas may be eligible for attainment date extensions, which is determined through the SIP process and 

should not be relevant for the first conformity determination under the 2006 PM2.5 NAAQS. Please consult 

the appropriate EPA Regional Office (see Section 1.5) for more information. 

20
areas, but please refer to the multi-jurisdictional guidance for further information 

regarding how a regional emissions analysis could be completed for these areas. 

More than one MPO. Where 1997 PM2.5 budgets cover more than one MPO, the 

planning agencies will have to work together to develop one regional emissions analysis 

for the entire 2006 PM2.5 area under 40 CFR 93.109(e)(2)(i), just as they have been doing 

for the 1997 PM2.5 NAAQS. MPOs must coordinate their plan/TIP conformity 

determinations and submit them to DOT. Once DOT receives all plan/TIP conformity 

determinations for the 2006 PM2.5 area, DOT will make its conformity determinations at 

the same time. 

Subarea budgets. Where subarea budgets31 exist for the 1997 PM2.5 NAAQS, EPA 

believes that these subarea budgets must also be used in the 2006 PM2.5 conformity 

determination, because using the existing budgets will ensure that air quality progress to 

date is maintained. In general, where a 2006 PM2.5 area has multiple MPOs with subarea 

budgets for the 1997 PM2.5 NAAQS, EPA and DOT believe it is necessary for the first 

conformity determination under the 2006 PM2.5 NAAQS to be conducted as follows: 

each MPO would independently demonstrate conformity of its transportation plan and 

TIP for the 2006 PM2.5 NAAQS using its 1997 PM2.5 subarea budgets. All of the MPOs’ 

plan/TIP conformity determinations would be submitted to DOT for DOT to make its 

conformity determination. DOT will not make a conformity determination on any of the 

plans or TIPs from the 2006 PM2.5 area until every MPO in the area has made a 

conformity determinations for its plan and TIP. All MPOs in the 2006 PM2.5 area must 

have an initial valid conformity determination for the 2006 PM2.5 NAAQS by the end of 

the one-year grace period. If any do not, DOT will be unable to make a 2006 PM2.5

conformity determination for the 2006 PM2.5 area, and all of the MPOs’ plans and TIPs 

within that area would lapse.32 

Multi-state areas. For multi-state 2006 PM2.5 nonattainment areas, the fact that existing 

1997 PM2.5 budgets must be used preserves states’ ability to determine conformity 

independently from one another, if a state has already established budgets for its own 

state for the 1997 PM2.5 NAAQS. In other words, states can operate independently for 

conformity to the 2006 PM2.5 NAAQS if they have adequate or approved 1997 PM2.5

budgets for their portion of the nonattainment area. 

Specifically, conformity determinations for the 2006 PM2.5 NAAQS can be made in one 

state of a multi-state 2006 PM2.5 area if it has adequate or approved 1997 PM2.5 budgets 

 

31 Areas may have subarea budgets when there is more than one MPO in a nonattainment area (within one 

state) per 40 CFR 93.124(d); in this case, each MPO must meet its own subarea budgets. See Part 3 of the 

multi-jurisdictional guidance for more information. 

32 In general, for subsequent conformity determinations, the MPOs can make conformity determinations 

independently as long as all other MPOs in the area must have a conforming plan and TIP in place. If one 

subarea is in a conformity lapse, conformity determinations for new or revised plans and TIPs cannot be 

made in other subareas until the lapse ends. 

21
even if a lapse is occurring in another state in the 2006 PM2.5 area, or conformity had not 

yet been determined for the 2006 PM2.5 NAAQS in another state in the area. 

22
Section 4. Project-level Conformity Requirements in 2006 PM2.5 Areas 

4.1. Timing of Project-level Conformity Determinations for the 2006 PM2.5 NAAQS 

The one-year grace period for conformity in newly designated areas described in Section 

2.1 of this guidance also applies to project-level conformity determinations (including 

hot-spot analyses in certain cases) in 2006 PM2.5 nonattainment areas. At the end of the 

one-year grace period for conformity, requirements for project-level conformity 

determinations must be met for the 2006 PM2.5 NAAQS before any new federal 

approvals or authorizations for non-exempt FHWA and FTA projects can occur. 

For non-exempt FHWA or FTA projects, a conformity determination is typically 

completed as part of the National Environmental Policy Act (NEPA) process and prior to 

issuance of a categorical exclusion, finding of no significant impact, or record of decision 

under NEPA. If a non-exempt project still requires FHWA or FTA approval or 

authorization after the last day of the one-year grace period, a project-level conformity 

determination will be required for the 2006 PM2.5 NAAQS even if the project has already 

completed the NEPA process, or for multi-phase projects, even if other phases of the 

project have already been constructed. If no new FHWA or FTA approvals or 

authorizations are required for a non-exempt project after the end of the one-year grace 

period, then project-level conformity will not be required for the 2006 PM2.5 NAAQS. 

Before the end of the one-year grace period, FHWA or FTA could choose to make a 

project-level conformity determination that meets the conformity rule’s requirements. 

Please consult with the FHWA Division and FTA Regional Offices if you have questions 

concerning how project-level conformity determinations are addressed in the NEPA 

process. 

This information is also found in the PM Amendments proposed rule preamble Section 

III.B (74 FR 23026-8). 

4.2. General Requirements 

The existing conformity requirements that apply to PM2.5 areas (see Table 1 in 40 CFR 

93.109) also apply to 2006 PM2.5 nonattainment or maintenance areas: 

 Project-level conformity determinations. All FHWA/FTA non-exempt projects 

must have a project-level conformity determination (40 CFR 93.116(a)); 

 Hot-spot analyses. A PM2.5 hot-spot analysis is required only for certain kinds of 

projects (listed at 40 CFR 93.123(b)(1)); in all other cases, a hot-spot analysis is 

not required (according to 40 CFR 93.116(a)). 

23
 Interagency consultation. The procedures for interagency consultation found in a 

state’s approved conformity SIP or 40 CFR 93.105 must be used in making 

project-level conformity determinations. See specifically 40 CFR 93.105(c)(1)(i), 

and refer to Section 2.3 of this guidance for additional information about 

interagency consultation. 

 Compliance with PM2.5 SIP control measures in approved SIPs, if any. See 

Section 4.6 below. 

4.3. What is a hot-spot analysis? 

A hot-spot analysis is defined in 40 CFR 93.101 as an estimation of likely future 

localized PM2.5 pollutant concentrations and a comparison of those concentrations to the 

NAAQS. A hot-spot analysis assesses the air quality impacts on a scale smaller than an 

entire nonattainment area, including for example, congested roadway intersections and 

highways or transit terminals. Such an analysis is a means of demonstrating that a 

transportation project meets Clean Air Act conformity requirements to support state and 

local air quality goals with respect to potential localized air quality impacts. 

Note that in the PM Amendments proposed rule, EPA has proposed minor wording 

changes to the hot-spot rules at 40 CFR 93.116(a). These proposed changes, if finalized, 

would not affect the substantive requirements in EPA’s current hot-spot regulations. See 

Section IX of the preamble of the May 2009 PM Amendments proposal (74 FR 23037-

40) and proposed regulatory text in §93.116(a).

4.4. Which PM2.5 NAAQS has to be considered in a hot-spot analysis? 

 

A hot-spot analysis must consider any PM2.5 NAAQS for which an area has been 

designated nonattainment. A hot-spot analysis would have to demonstrate that the 

project meets the conformity rule’s hot-spot requirements for all of the PM2.5 NAAQS for 

which the area is designated nonattainment, e.g.: 

 if an area is designated nonattainment for only the 2006 24-hour NAAQS, the 

analysis would have to consider only that NAAQS; 

 if an area is designated nonattainment for the 1997 annual NAAQS and the 2006 

24-hour NAAQS, the analysis would have to consider both NAAQS; 

 if an area is designated nonattainment for both the 1997 annual and 24-hour 

NAAQS, as well as the 2006 24-hour NAAQS, the analysis would have to 

consider all of these NAAQS.33 

 

33 While both 24-hour NAAQS must be considered, in practice if the more stringent 2006 24-hour PM2.5

NAAQS is met, then the 1997 24-hour PM2.5 NAAQS is met as well. 

24
25

EPA and DOT will work with PM2.5 nonattainment areas as needed to ensure that state 

and local agencies can meet existing and new conformity requirements for the 2006 

PM2.5 NAAQS in a timely and efficient manner. If you need assistance regarding a hotspot analysis, see Section 1.5 of this guidance for contact information for EPA regional 

offices, and the following websites for FHWA division and FTA regional offices, 

respectively: 

http://www.fhwa.dot.gov/field.html

http://www.fta.dot.gov/regional_offices.html 

4.5. Where can I find more information about PM2.5 hot-spot analyses? 

Please refer to the March 10, 2006 final rule for additional information regarding PM hotspot analyses (71 FR 12468) and EPA and FHWA’s current guidance for implementing 

this requirement, entitled, “Transportation Conformity Guidance for Qualitative Hot-spot 

Analyses in PM2.5 and PM10 Nonattainment and Maintenance Areas,” March 2006, 

(EPA420-B-06-902). This guidance can be found on EPA’s website at: 

http://www.epa.gov/otaq/stateresources/transconf/policy/420b06902.pdf 

The qualitative hot-spot guidance answers questions such as: 

 What projects need a PM2.5 hot-spot analysis? 

 What methods can be used for performing qualitative PM2.5 hot-spot analyses? 

 What should be documented for a qualitative PM2.5 hot-spot analysis? 

 What emissions are considered in a PM2.5 conformity analysis for a project? 

 What time frame and analysis years should be used in hot-spot analyses? 

Note that the qualitative guidance is to be used for hot-spot analyses until the requirement 

for quantitative analysis takes effect. During the time that this interim guidance is in 

effect, PM2.5 hot-spot analyses will be done qualitatively.34 

4.6. Compliance with PM2.5 SIP Control Measures 

In PM2.5 areas, the conformity rule at 40 CFR 93.117 requires that before FHWA and 

FTA projects can be determined to be in conformity, written commitments from the 

project sponsor or operator to implement any PM2.5 project-level mitigation or control 

measures in an approved SIP must be obtained. See EPA’s July 2004 final rule for 

further information on this requirement (69 FR 40036-40037). 

 

34 The requirements for quantitative analysis will take effect when EPA releases modeling guidance on this 

subject and announces it in the Federal Register, based on the regulation at 40 CFR 93.123(b)(4). EPA 

will establish a grace period before quantitative analysis is required. See EPA’s website at: 

http://www.epa.gov/otaq/stateresources/transconf/policy.htm for upcoming MOVES SIP and conformity 

policy guidance, including upcoming quantitative hot-spot modeling guidance.