Guidance for Transportation Conformity

Implementation in Multi-Jurisdictional

Nonattainment and Maintenance Areas 
Transportation and Climate Division

Office of Transportation and Air Quality

U.S. Environmental Protection Agency

Guidance for Transportation Conformity

Implementation in Multi-Jurisdictional

Nonattainment and Maintenance Areas 

EPA-420-B-12-046

July 2012
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Table of Contents 

Section 1: Introduction 6

1.1 What is the purpose of this guidance? ................................................................................ 6

1.2 Who can I contact for more information? ........................................................................... 7

1.3 Does this guidance create new conformity requirements? ................................................. 7

1.4 What is a multi-jurisdictional area? .................................................................................... 8

1.4.1 One MPO, One State (not a multi-jurisdictional area) ......................................... 9

1.4.2 More than One MPO ............................................................................................ 9

1.4.3 Donut Areas ........................................................................................................ 10

1.4.4 Multi-State Areas ................................................................................................ 11

1.4.5 One MPO that Covers More Than One Nonattainment or Maintenance Area .. 12

1.5 What are the general requirements for interagency consultation when determining 

conformity for a transportation plan/TIP? ........................................................................ 13

1.6 Who is responsible for estimating emissions in a donut area of a nonattainment or 

maintenance area? ............................................................................................................. 13

Section 2: Conformity Determinations and Regional Emissions Analyses in Areas 

without Any Budgets 15

2.1 To what areas does this section of the guidance apply? ................................................... 15

2.2 What tests are used for the regional emissions analysis before a nonattainment area has 

budgets for a relevant pollutant? ....................................................................................... 15

2.3 What geographic area must be examined in regional emissions analyses and conformity 

determinations before a nonattainment area has budgets? ................................................ 15

2.4 How can multiple agencies create a regional emissions analysis for the entire 

nonattainment area? .......................................................................................................... 16

2.4.1 More Than One MPO, in One or More States (without a Donut Area) ............. 17

2.4.2 One or More MPOs and a Donut Area ............................................................... 17

2.4.3 Coordinating Transportation Plan and TIP Update and Amendment Cycles 

among MPOs ...................................................................................................... 18

2.5 What decisions must be made in the interagency consultation process? .......................... 19

2.6 If one MPO in the area can meet the requirements of 40 CFR 93.119, but another MPO or 

a donut area cannot, can the MPO that meets the requirements show that its transportation 

plan and TIP conform and proceed? ................................................................................. 21

Section 3: Conformity Determinations and Regional Emissions Analyses with SIP 

Budgets for the Relevant NAAQS 23

3.1 What does this section of the guidance cover? ................................................................. 23

3.2 How do nonattainment and maintenance areas determine conformity for a given NAAQS 

once budgets are available for that NAAQS? ................................................................... 23
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3.3 What geographic areas might budgets from a SIP cover, and how is conformity generally 

determined in multi-jurisdictional areas with budgets? .................................................... 24

3.4 How is conformity demonstrated when budgets are established for an entire 

nonattainment or maintenance area that is within one state? ............................................ 26

3.4.1 More than One MPO .......................................................................................... 26

3.4.2 One or More MPOs and a Donut Area ............................................................... 26

3.4.3 Coordinating Transportation Plan and TIP Update and Amendment Cycles 

among MPOs ...................................................................................................... 27

3.5 How is conformity demonstrated when there is more than one MPO in a single state and 

the SIP establishes subarea budgets for each MPO? ........................................................ 28

3.6 Can an MPO that has its own subarea budgets determine conformity of its transportation 

plan and/or TIP when another MPO in the same area is in a conformity lapse or 

conformity lapse grace period? ......................................................................................... 30

3.6.1 Conformity Lapse ............................................................................................... 30

3.6.2 Conformity Lapse Grace Period ......................................................................... 31

3.7 Can a subarea budget be established for a donut area? ..................................................... 31

3.8 If a SIP establishes only subarea budgets, do MPOs have the option to use either an areawide SIP budget or subarea budgets? ............................................................................... 32

3.9 How do multi-state nonattainment and maintenance areas determine conformity if each 

state submits a SIP that contains the same budgets for the entire multi-state area? ......... 32

3.10 When would it be likely for state air agencies in a multi-state nonattainment or 

maintenance area to submit SIPs with budgets that apply to the entire area? .................. 33

3.11 How is conformity determined for multi-state nonattainment or maintenance areas when 

each state has a SIP that contains budgets only for its own state’s portion of the area? .. 34

3.12 How is conformity determined for a multi-state nonattainment or maintenance areas 

when one state has a budget for a NAAQS and the other state(s) does not have budgets 

for that pollutant? .............................................................................................................. 34

Section 4: Conformity Determinations and Regional Emissions Analyses with SIP 

Budgets for Another NAAQS of the Same Pollutant 35

4.1 To what areas does this section of the guidance apply? ................................................... 35

4.2 What scenarios could result when determining conformity for a NAAQS using a budget 

from another NAAQS of the same pollutant?................................................................... 35

4.3 What are the general test requirements for regional emissions analyses for these areas? 36

4.4 How is the budget test generally implemented in areas that do not have a budget for the 

relevant NAAQS but have a budget for another NAAQS of the same pollutant? ............ 37

4.5 Where relevant NAAQS areas have to use both the budget test and the interim emissions 

test(s), what analysis years must be chosen? .................................................................... 39
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4.6 In an area that has subarea budgets for another NAAQS of the same pollutant, how 

should MPOs demonstrate conformity for the first time under the relevant NAAQS and 

for subsequent conformity determinations? ...................................................................... 40

4.7 How would conformity be demonstrated in multi-state areas where each state has its own 

budget for another NAAQS of the same pollutant? .......................................................... 41

4.8 How is conformity demonstrated in Scenario 1 areas where one budget (or one set of 

budgets) apply for the entire area? .................................................................................... 42

4.9 How is conformity demonstrated in a Scenario 1 area when subarea budgets have been 

established? ....................................................................................................................... 43

4.10 How is conformity demonstrated in multi-state Scenario 1 areas, where each state has its 

own budget? ...................................................................................................................... 43

4.11 How is conformity demonstrated in a Scenario 2 area, when the budget applies to the 

entire area for the relevant NAAQS? ................................................................................ 44

4.12 How is conformity demonstrated in multi-state Scenario 2 areas, where each state has its 

own budget? ...................................................................................................................... 45

4.13 How is conformity demonstrated in a Scenario 3 area located entirely within one state? 46

4.14 How is conformity demonstrated in a Scenario 3 area located entirely within one state, 

when subarea budgets apply?............................................................................................ 47

4.15 How is conformity demonstrated in a multi-state Scenario 3 area, where all the states 

have their own budgets?.................................................................................................... 48

4.16 How is the regional emissions analysis done in multi-state Scenario 3 areas, where only 

one of the states has its own budget(s)? ............................................................................ 50

4.17 What are the special issues that the interagency consultation process should consider in 

Scenario 3 areas?............................................................................................................... 50

4.18 How is conformity demonstrated in a Scenario 4 area, when one budget applies for the 

entire area rather than subarea budgets? ........................................................................... 51

4.19 How does a multi-state Scenario 4 area determine conformity, when each state has its 

own budget(s)? .................................................................................................................. 53

4.20 How is the regional emissions analysis done in a multi-state Scenario 4 area, where only 

one of the states has its own budget? ................................................................................ 53

4.21 What are special issues that the interagency consultation process should consider in 

Scenario 4 areas?............................................................................................................... 54
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Section 1: Introduction 

1.1 What is the purpose of this guidance? 

This guidance describes how transportation conformity determinations are done in areas where 

multiple metropolitan planning organizations (MPOs), states, and/or other agencies have 

jurisdiction in a nonattainment or maintenance area. This guidance updates and supersedes the 

July 2004 “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). In the 2004 guidance, EPA 

clarified how transportation conformity determinations are completed where multiple agencies or 

states are involved in nonattainment and maintenance areas specifically for the 1997 ozone and 

PM2.5 National Ambient Air Quality Standards (NAAQS). EPA’s transportation conformity rule 

(40 CFR Parts 51 and 93) establishes the criteria and procedures for determining whether 

transportation plans, transportation improvement programs (TIPs), and federally funded or 

approved highway and transit projects are consistent with (“conform to”) state air quality goals. 

This updated guidance is being released as part of a larger EPA effort to restructure the 

transportation conformity regulations so that they apply to existing and future NAAQS. EPA 

published the Transportation Conformity Rule Restructuring Amendments (“Conformity 

Restructuring” rule) on March 14, 2012 (77 FR 14979), which restructures two sections of the 

transportation conformity rule so that existing requirements apply for any NAAQS, including 

new or revised NAAQS promulgated in the future. This guidance describes how the provisions 

that were updated in the Conformity Restructuring rule apply in various types of areas and will 

assist state and local governments in implementing conformity requirements. It does not change 

the substance of the 2004 guidance for addressing conformity requirements in multijurisdictional areas because the revisions to the conformity regulations did not change the 

requirements for the conformity tests. This guidance reflects the revised structure of the 

conformity regulations issued in the Conformity Restructuring rule.

Specifically, this guidance covers questions for multi-jurisdictional areas such as:

• What geographic area is covered by a conformity determination and regional emissions 

analysis?1

• How is the regional emissions analysis implemented?

• Who does what to develop the regional emissions analysis? 

• What regional emissions test or tests apply for multi-jurisdictional areas that have 

adequate or approved State Implementation Plan (SIP) motor vehicle emissions budgets 

(“budgets”) for a specific transportation-related criteria pollutant?2

• How can multiple agencies create a regional emissions analysis for the entire 

nonattainment area before the area has SIP budgets for a relevant criteria pollutant?

 

1 A regional emissions analysis is the part of a conformity determination that assesses whether the emissions 

produced by transportation activities are consistent with state air quality goals. See 40 CFR 93.122 for details.

2 Transportation conformity applies in nonattainment areas and areas designated attainment after 1990 

(“maintenance areas”) for ozone, carbon monoxide, nitrogen dioxide, PM10 and PM2.5 (40 CFR 93.102(b)).
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This guidance covers both existing and future nonattainment and maintenance areas and 

highlights opportunities for flexibility. It provides examples and interpretations for generic 

scenarios involving regional emissions analyses that may occur in the field. In the event 

implementers have questions that are not addressed in this guidance, they should consult EPA

and the U.S. Department of Transportation (DOT). 

DOT is EPA’s federal partner in implementing the conformity regulation. DOT participated in 

the development of this guidance and concurred on its content. 

The interagency consultation process is of key importance in multi-jurisdictional areas. Given 

the fact that no two areas that implement conformity are exactly alike, the interagency 

consultation process must be used to make the best choices for an area’s circumstances where the 

conformity rule provides flexibility. The interagency consultation provision of the conformity 

rule, 40 CFR 93.105, requires that general processes and specific decisions be made through 

established interagency consultation procedures. 

 

1.2 Who can I contact for more information?

For specific questions concerning a particular nonattainment or maintenance area, please contact 

the conformity staff person responsible for your state at the appropriate EPA regional office, 

Federal Highway Administration (FHWA) division office or Federal Transit Administration 

(FTA) regional office:

• A listing of the EPA Regions, the states they cover, and contact information for 

conformity staff can be found at the following website: 

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

• Contact information for FHWA division offices can be found at: 

http://www.fhwa.dot.gov/about/field.cfm 

• Contact information for FTA regional offices can be found at: 

http://www.fta.dot.gov/about/12926.html 

General questions about this guidance can be directed to EPA’s Office of Transportation and Air 

Quality: Laura Berry at berry.laura@epa.gov or (734) 214-4858, or Meg Patulski at

patulski.meg@epa.gov or (734) 214-4842. 

Readers can also find this guidance document, the complete transportation conformity 

regulation, and other materials on EPA’s website at: 

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

1.3 Does this guidance create new conformity requirements?

No. This guidance is based on the requirements for conformity implementation contained in 

CAA section 176(c) and 40 CFR Parts 51.390 and 93 Subpart A. This guidance does not create 

any new conformity requirements. This guidance merely explains how to implement conformity 

requirements in multi-jurisdictional areas. 
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The statutory provisions and the EPA regulations described in this document 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. EPA retains the discretion to adopt approaches on a case-by-case basis that may 

differ from this guidance, but still comply with the statute and conformity and other regulations. 

This guidance may be revised periodically without public notice. 

1.4 What is a multi-jurisdictional area?

A multi-jurisdictional area is a nonattainment or maintenance area with several agencies (e.g., 

MPOs, state agencies) that conduct transportation and/or air quality planning. Multijurisdictional areas are nonattainment and maintenance areas that:

• Have multiple MPOs, or 

• Have one or more MPOs and a donut area, and/or

• Are located in more than one state. 

One MPO that covers more than one nonattainment or maintenance area would also be 

considered a multi-jurisdictional area. The MPO is the agency that is responsible for preparing 

metropolitan transportation plans (hereafter called “transportation plans”) and TIPs and 

demonstrating that transportation plans and TIPs conform to the purpose of the SIP before they 

are adopted. An MPO is established for each metropolitan area according to Section 134 of Title 

23, United States Code and Section 5303 of Title 49, United States Code. The conformity rule at 

40 CFR 93.101 includes the following definition of an MPO: 

“...the policy board of an organization created as a result of the 

designation process in 23 U.S.C. 134(d).” 

MPO planning boundaries are established according to Titles 23 and 49 of the United States

Code (as cited above) and DOT’s metropolitan planning regulations. The conformity rule does 

not dictate how MPO planning boundaries are established. 

In most cases, a conformity determination for a transportation plan, TIP, or project not from a 

conforming transportation plan or TIP includes a regional emissions analysis in which emissions 

from the planned transportation system are estimated according to 40 CFR 93.122. 

Whether a nonattainment or maintenance area contains more than one MPO, a donut area, and/

or is located within more than one state, the conformity regulation process includes flexibility to 

accommodate the many differences in state and local agency roles and planning processes across 

the country. 

Sections 1.4.1 through 1.4.5 describe different situations of nonattainment/maintenance area 

boundaries, MPO boundaries, and state boundaries. 
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1.4.1 One MPO, One State (not a multi-jurisdictional area)

To contrast the remainder of this guidance, first it is useful to describe a conformity 

determination in the case where there is a single jurisdiction responsible for transportation

planning and a single jurisdiction responsible for air quality planning. In the simplest case, a 

nonattainment or maintenance area is located entirely within one state, and the boundary of the 

nonattainment or maintenance area is exactly the same as the MPO boundary, as shown in Figure 

1.1 below. 

This is not a multi-jurisdictional area. In this situation, there is just one MPO responsible for 

transportation planning and conformity determinations in the area and one air quality agency 

responsible for air quality planning. There is no donut area within the nonattainment or 

maintenance area and the area is located in just one state.

1.4.2 More than One MPO

The MPO boundary may not correspond to the nonattainment or maintenance area boundary, nor 

is a nonattainment or maintenance area always covered by a single MPO. In these cases, there 

may be more than one MPO responsible for transportation planning and conformity 

determinations in the nonattainment or maintenance area, as shown in Figure 1.2 below. 
10 

 

1.4.3 Donut Areas

There may be other cases where some portion of the nonattainment or maintenance area is not 

included in an MPO’s jurisdiction, also known as a “donut area.” As defined in 40 CFR 93.101: 

“Donut areas are geographic areas outside a metropolitan planning 

area boundary, but inside the boundary of a nonattainment or 

maintenance area that contains any part of a metropolitan area(s). 

These areas are not isolated rural nonattainment and maintenance 

areas.”

If the nonattainment or maintenance area includes an MPO, any areas outside of the MPO(s) 

boundaries would be the donut area(s). Though the word “donut” implies that the boundary of 

the MPO would be entirely within the nonattainment or maintenance area boundary to form two 

concentric circles, a nonattainment or maintenance area’s donut area may more typically 

resemble that shown in Figure 1.3 below. Donut areas could exist as part of a single state or 

multi-state nonattainment or maintenance area.
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1.4.4 Multi-State Areas

There are also cases where a nonattainment or maintenance area’s boundary includes parts of 

more than one state, as shown in Figures 1.4a and 1.4b below. One MPO may cover the entire 

multi-state nonattainment or maintenance area (Figure 1.4a), or separate MPOs may cover each 

state’s portion of the area (Figure 1.4b). These multi-state areas may also include donut areas in 

one or more states.
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1.4.5 One MPO that Covers More Than One Nonattainment or Maintenance Area

Finally, there are some MPOs that are responsible for transportation planning and conformity 

determinations in more than one nonattainment or maintenance area. This guidance applies to 

such MPOs as well. The November 24, 1993 conformity rule preamble addresses the case where 

an MPO is responsible for more than one area, which continues to apply: 

“If a metropolitan planning area includes more than one 

nonattainment area, a conformity determination must be made for 

each nonattainment area. Emissions budgets established in the 

SIP(s) for the included nonattainment areas may not be combined 

or reallocated. Build/no-build tests must be applied separately in 

each nonattainment area” (58 FR 62208). 

In these cases, a single MPO that is responsible for transportation planning for more than one 

nonattainment or maintenance area must determine conformity for each nonattainment or 

maintenance area separately. 

As an example, suppose an MPO encompasses two counties, as illustrated in Figure 1.5. One of 

these counties is located in one PM2.5 nonattainment area (Area A), while the other county is 

located in another, adjacent PM2.5 nonattainment area (Area B).

Sections 2 through 4 of this guidance include details for how conformity would be determined 

for the portion of such an MPO’s transportation plan and TIP for each nonattainment or 

maintenance area.
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1.5 What are the general requirements for interagency consultation when 

determining conformity for a transportation plan/TIP? 

Interagency consultation is required in all nonattainment and maintenance areas where 

conformity applies. Interagency consultation procedures for a nonattainment or maintenance 

area are formally integrated into the conformity SIP and are legally enforceable.3 A state’s 

conformity SIP, or the federal regulations at 40 CFR 93.105 govern the decision-making process 

and specifically require that a process be established to evaluate and choose a model, associated 

methods, and assumptions to be used in the regional emissions analysis. 

Interagency consultation ensures that agencies involved in the conformity process meet 

regularly, share information, and identify key issues early in the conformity process. 

Additionally, the process ensures that schedules are coordinated for transportation plan/TIP 

conformity determinations and SIP development. 

The agencies responsible for the conformity determination and regional emissions analysis in 

multi-jurisdictional nonattainment and maintenance areas must develop interagency consultation 

procedures to address certain decisions such as:

• The timing of individual transportation plan and TIP conformity determinations in those 

circumstances where they need to be coordinated; 

• The analysis years that will be examined in the regional emissions analysis;

• The agency that will analyze emissions for any donut area that is part of the 

nonattainment or maintenance area (see Section 1.6 for more information); 

• The emissions model to be used for the regional emissions analysis, in the case where 

there is more than one emissions model that could be used (e.g., during a new model 

grace period), per 40 CFR 93.111; 

• The planning assumptions to be used in the regional emissions analysis and the sources of 

that information. 

Per 40 CFR 93.105(b)(1), state air agencies must use the interagency consultation process in

developing SIP budgets, including establishing subarea budgets for MPOs or individual state 

budgets in multi-jurisdictional areas.

1.6 Who is responsible for estimating emissions in a donut area of a 

nonattainment or maintenance area? 

In a nonattainment or maintenance area with a donut area, the lead agency for developing the 

regional emissions analysis that applies to the donut area can be:

• The MPO within the nonattainment or maintenance area. In some cases, an adjacent 

MPO is best suited to conduct such an analysis. An MPO could run a separate analysis 

 

3 For additional information on conformity SIPs, please refer to the January 2009 guidance entitled, “Guidance for 

Developing Transportation Conformity State Implementation Plans” available on EPA’s website at 

www.epa.gov/otaq/stateresources/transconf/policy/420b09001.pdf. 
14 

for the donut area’s projects and add the emissions to the MPO’s analysis. The MPO 

could also include the donut area’s projects in its regional model and estimate emissions 

for the entire area. An MPO could also include the donut area’s projects in its 

transportation plan and TIP, but this practice is not common; 

• The state DOT. In some cases, the state DOT may take the lead in estimating emissions 

for the donut area and provide the results to the MPO; or 

• Another local planning agency. In limited cases, another local planning agency in the 

donut area (e.g., a county planning commission) may also be the lead agency for the 

donut area. 

The conformity rule at 40 CFR 93.105(c)(3) relies on the interagency consultation process 

(including the MPO and state DOT) to determine how best to consider projects that are planned 

for donut areas located outside the metropolitan area and within the nonattainment or 

maintenance area in the conformity process. Section 93.105 of the conformity rule also requires 

that such procedures for demonstrating conformity of donut area projects be included in an area’s 

conformity SIP that is approved by EPA, according to 40 CFR 51.390. 
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Section 2: Conformity Determinations and Regional Emissions 

Analyses in Areas without Any Budgets

2.1 To what areas does this section of the guidance apply?

Section 2 of this guidance applies to areas that are determining conformity for a NAAQS but do 

not yet have any budgets for that pollutant. 

This section of the guidance does not cover:

• Areas that have a budget for the NAAQS for which they are designated nonattainment 

(the relevant NAAQS);

• Areas that have a budget for another NAAQS of the same pollutant; 

• Maintenance areas, as these areas by definition have approved SIPs with budgets, in most 

cases.

2.2 What tests are used for the regional emissions analysis before a 

nonattainment area has budgets for a relevant pollutant?

Conformity applies for a NAAQS one year after the effective date of EPA’s nonattainment 

designation for that NAAQS typically before an area is able to submit a SIP for the NAAQS 

containing budgets and those budgets are found adequate. If an area does not have an adequate 

or approved budget(s) for the relevant NAAQS or another NAAQS of the same pollutant, the 

regional emissions analysis and conformity determination must be based on the interim 

emissions test(s) (40 CFR 93.109(c)(3)). The interim emissions tests, described in 40 CFR 

93.119, include different forms of the “build/no-build” test and “baseline year” test. 

In general, the regional emissions analysis using the build/no-build test compares emissions from 

the planned (or “build”) transportation system in an analysis year with emissions from the 

existing (or “no-build”) transportation system in the same analysis year. In the baseline year test, 

emissions from the planned transportation system in an analysis year are compared to emissions 

that occurred in the relevant baseline year.

2.3 What geographic area must be examined in regional emissions analyses 

and conformity determinations before a nonattainment area has 

budgets?

A conformity determination for a transportation plan, TIP, or project not from a conforming plan 

or TIP must be based on a regional emissions analysis that covers the entire nonattainment area, 

to satisfy the statute and regulations (40 CFR 93.122(a)(1)). 
16 

There must be a regional emissions analysis for the entire nonattainment area, whether the 

nonattainment area includes one MPO or more than one MPO, a donut area, portions of more 

than one state, or any combination of these jurisdictions. 

For all nonattainment areas covered by this section, the MPO(s) must complete their 

transportation plan/TIP conformity determinations for the entire nonattainment area and 

coordinate their conformity determinations, pursuant to 40 CFR 93.124(d). Specifically, 40 CFR 

93.124(d) states: 

“If a nonattainment area includes more than one MPO, the 

implementation plan may establish motor vehicle emissions 

budgets for each MPO, or else the MPOs must collectively make a 

conformity determination for the entire nonattainment area.”

Once DOT receives all transportation plan/TIP conformity determinations for MPOs in a given 

nonattainment area, DOT will make its conformity determinations at the same time. In order for 

one MPO to update or revise its transportation plan and TIP, a DOT conformity determination 

for each transportation plan and TIP in that nonattainment area must be made at the same time, 

according to 40 CFR 93.124(d). See Section 2.4.3 on coordinating transportation plan and TIP 

update cycles among MPOs. Therefore, in cases where no budgets exist, the MPOs would not be 

making conformity determinations for transportation plans and TIPs on independent schedules, 

but on the same schedule. 

EPA believes that it is necessary for conformity determinations and regional emissions analyses 

to include the entire nonattainment area when there are no budgets to ensure that the 

requirements of CAA section 176(c)(1) are met. That is, before budgets become available, in 

order to determine that transportation activities will not cause a new air quality violation, 

increase the frequency or severity of a violation, or delay timely attainment of the relevant 

NAAQS and interim milestones, it is necessary to consider emissions from the entire area in one 

regional emissions analysis, and for DOT to make all transportation plan/TIP conformity 

determinations at the same time.

2.4 How can multiple agencies create a regional emissions analysis for the 

entire nonattainment area?

The agencies involved in the conformity process in a nonattainment area where there is more 

than one MPO and/or a donut area must use the interagency consultation process required by 40 

CFR 93.105 to decide how best to meet this requirement, regardless of whether the area is within 

one state or is a multi-state area. The interagency consultation process would be used to decide 

which interim emissions tests apply and what analysis years are used. MPOs must use the same 

tests and analysis years for the entire nonattainment area, as described in Section 2.5 of this 

guidance. 
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2.4.1 More Than One MPO, in One or More States (without a Donut Area)

In a nonattainment area where there is more than one MPO, the MPOs can develop the regional 

emissions analysis using either of the below options: 

Option 1: By separate modeling by each MPO that is combined into one regional 

emissions analysis for the entire nonattainment area

Option 2: By one modeling analysis for the entire nonattainment area

If MPOs in the nonattainment area want to model their emissions separately (Option 1), each 

MPO would perform a regional emissions analysis that would show that the applicable interim 

emissions test(s) are met for each analysis year under the regulations. These results would then 

be compiled in one regional emissions analysis for the entire nonattainment area that would 

accompany each transportation plan/TIP conformity determination. The MPOs in the 

nonattainment area can work independently to complete the regional emissions analysis for their 

own parts of the area, but a single analysis would be combined for the entire nonattainment area 

to satisfy conformity requirements for each MPO’s transportation plan/TIP. 

Alternatively, the regional emissions analysis could be completed by showing that the emissions 

in each analysis year for the entire nonattainment area meet the applicable interim emissions 

test(s) (Option 2). The MPOs in the area would work together to carry out a regional emissions 

analysis for the entire nonattainment area that includes all of their transportation plans and TIPs. 

Again, these modeling results would be presented in one regional emissions analysis for the 

entire nonattainment area that would accompany each transportation plan/TIP conformity 

determination. 

For example, suppose there are multiple MPOs within a nonattainment area and they are 

demonstrating conformity using the build/no-build test. If each MPO has its own travel demand 

model and prefers to run its own analysis, all MPOs must choose the same analysis years. The 

analysis must show either that each MPO passes its own build/no-build test; or the “build” 

scenarios and the “no-build” scenarios from each MPO must be aggregated, and the total “build” 

emissions from all MPOs must be less than the total “no-build” emissions from all MPOs. 

Alternatively, the MPOs could coordinate in creating one regional emissions analysis for the 

entire nonattainment area that meets the build/no-build test.

2.4.2 One or More MPOs and a Donut Area

If there is only one MPO in the nonattainment area conducting conformity determinations and a 

donut area exists, the conformity rule requires the MPO to include the emissions estimated from 

the donut area in the regional emissions analysis for the MPO’s transportation plan and TIP 

conformity determinations. However, either the MPO or the state DOT could estimate emissions 

from the donut area as decided through interagency consultation. See below for details. 

If there is more than one MPO as well as a donut area in a nonattainment area, the MPOs must 

work together and with the state DOT, as appropriate, to create one regional emissions analysis 
18 

for the entire nonattainment area that would accompany each transportation plan/TIP conformity 

determination. The emissions estimated from the entire area must meet the interim emissions 

test or tests, according to the requirements of 40 CFR 93.119. Again, the interagency 

consultation process would be used to coordinate the choice of tests (as applicable) and analysis 

years when several agencies are completing emissions analyses, because the same tests and 

analysis years must be used as noted above. 

If a project-level conformity determination is required for a new project in a donut area, the 

project would first need to be included in the associated MPO’s transportation plan and TIP’s 

conformity determination (including the regional emissions analysis) before the project-level 

conformity determination can proceed. There must be a currently conforming transportation 

plan and TIP at the time of project approval,4

 and for each MPO, only one transportation plan or 

TIP conformity determination (including the regional emissions analysis) may exist at any time 

(40 CFR 93.114). See Section 3.7 for when a donut area can operate independently from an 

adjacent MPO(s) for project approvals. 

Note that in the preamble to the November 24, 1993 final rule (58 FR 62207-62208), EPA 

described another option that EPA no longer believes is viable, and therefore, this option is not 

included in this guidance. The option was described in the preamble to the 1993 rule as follows: 

a new regional emissions analysis (separate from that completed for the MPO’s transportation 

plan and TIP) could be completed that hypothetically assumed a new donut area project would 

be added to the transportation plan and TIP, and the combination of emissions would be tested to 

see if it would satisfy all the conformity criteria for transportation plans and TIPs. EPA 

indicated in the preamble to the 1993 rule that this approach was not preferred, and that it would 

be better to include the project in the regional emissions analysis. Since the 1993 rule, this 

option has not been used, and as a result MPO transportation plan and TIP conformity 

determinations have been able to meet 40 CFR 93.114. The hypothetical analysis approach 

described in the 1993 rule preamble would effectively lead to having two separate regional 

emissions analyses for the same transportation plan and TIP – a hypothetical one that includes 

the donut project and an actual one that does not comply with this requirement of the conformity 

rule. This clarification in today’s guidance on this option continues to implement the conformity 

rule consistent with past practice. 

2.4.3 Coordinating Transportation Plan and TIP Update and Amendment Cycles among MPOs

All MPOs must use the same test and the same analysis years for the regional emissions analysis 

regardless of whether each MPO creates an analysis for its geographic area which is then 

aggregated, or the MPOs coordinate to create one analysis. MPOs in the same nonattainment 

area may want to coordinate their transportation plan and TIP update cycles as well as the 

timeframe of the conformity determination, as described below: 

• Updated transportation plans and TIPs or amendments that include non-exempt projects, 

require a new conformity determination and may require a new regional emissions 

 

4 Except during the lapse grace period, when a project can come from the most recent conforming transportation 

plan and TIP (or regional emissions analysis). Refer to Section 3.6.2.
19 

analysis (see 40 CFR 93.104 and 93.122(g)). When one of the MPOs in the area wants to 

update its transportation plan or TIP or make an amendment that includes one or more 

non-exempt projects, the other MPOs can rely on their portion of a previous regional 

emissions analysis for the conformity determination provided that they meet the criteria 

in 40 CFR 93.122(g).5

 Coordination of transportation plan and TIP update and 

amendment cycles among MPOs in the same nonattainment area may minimize the 

number of new regional emissions analyses and conformity determinations that have to 

be completed.

• Where one of the MPOs in the multi-jurisdictional area wants to update its transportation 

plan and TIP or make an amendment that includes one or more non-exempt projects, the 

public involvement requirements of 40 CFR 93.105(e) of the conformity rule would 

apply for all MPOs, including a public comment period on all MPO transportation 

plan/TIP conformity determinations. However, the requirements under DOT’s 

transportation planning requirements (23 CFR 450.316(b)) would not apply in this 

situation (including the requirement to hold a public hearing) for any MPOs that are not 

updating or amending their transportation plans or TIPs. 

• MPOs may have to analyze additional years if the timeframes of their conformity 

determinations differ. According to 40 CFR 93.119(g), an analysis must be performed 

for the last year of the timeframe of the conformity determination (generally, the last year 

of the transportation plan’s forecast period).6

 For example, if one MPO’s transportation 

plan forecast period ends in 2035 and another MPO’s transportation plan forecast period 

ends in 2040, both years would have to be analyzed in the regional emissions analysis for 

the entire nonattainment area. Coordination of transportation plan forecast periods may 

minimize the number of analysis years that have to be examined in any one regional 

emissions analysis.

2.5 What decisions must be made in the interagency consultation process?

The agencies responsible for the conformity determination and regional emissions analysis in a 

nonattainment area, which are the MPOs and possibly the state DOT(s) for a donut area in a 

nonattainment area, must use the interagency consultation process to make certain decisions. Per 

the conformity rule, there are certain aspects of conformity that must be consistent across the 

nonattainment area, even when there are more than one MPO and they each model their own 

portion separately, as described earlier in the guidance. Aspects that must be consistent include: 

• Timing of individual plan and TIP conformity determinations, so that DOT can make its 

conformity determinations for all transportation plans and TIPs in a nonattainment area at 

the same time;

 

5 This provision allows a conformity determination to be made without a new regional emissions analysis if the 

previous regional emissions analysis still applies. Please refer to the conformity regulation for more information.

6 The timeframe of a conformity determination could be shortened per 40 CFR 93.106(d).
20 

• How the regional emissions analysis is developed, e.g., whether emissions will be 

modeled for each MPO’s jurisdiction separately and summed together, or modeled for the 

nonattainment area as a whole;7

• The interim emissions test that will be used in nonattainment areas that have a choice of 

interim emissions test.8 

EPA believes that for consistency and in order to satisfy the requirements of the 

conformity rule, the same test must be used in all portions of the nonattainment area in 

areas that have the choice of interim emissions tests for a given conformity 

determination. In other words, it would not be acceptable for one MPO to use the 

build/no-build test and another MPO within the same nonattainment area to use the 

baseline year test, because 40 CFR 93.119 and 93.124(d) require that one test be met for 

the entire nonattainment area where only one test is required. 

The same test would be required to be used for each analysis year for a given conformity 

determination as well. EPA believes that sufficient flexibility exists without using 

different interim emissions tests for different analysis years within one conformity 

determination, which is unnecessarily complicated and may indicate that an area would 

not conform using one test consistently. 

• The analysis years that will be used for the interim emissions test(s), as required by 40 

CFR 93.119(g). 

Again, EPA believes that analysis years must be consistent in all portions of the 

nonattainment area, even if emissions are modeled for each MPO’s jurisdiction 

separately; otherwise, they cannot be summed together to produce a complete analysis to 

satisfy the test. Regional emissions analyses for all MPOs must cover the same time 

period and thus need to include the last year of each transportation plan or conformity 

determination as an analysis year.

For example, if the last year of one MPO’s transportation plan is 2035 and the last year of 

another MPO’s transportation plan is 2040, the regional emissions analyses for both 

MPOs must examine emissions in the years 2035 and 2040.9

 

• Who will analyze emissions for any donut area that is part of the nonattainment area? As 

mentioned above, any of the MPOs, the state DOT, or a local planning agency could 

 

7 Please note that there may be different travel activity models and methods used among MPOs and/or donut areas in 

a multi-jurisdictional area. Such differences between jurisdictions are acceptable as long as each MPO/donut area is 

using the latest models and methods available and 40 CFR 93.122 requirements are met. 8 Areas that have a choice of interim emissions tests include: Marginal and below ozone nonattainment areas and 

other ozone nonattainment areas that are not subject to reasonable further progress requirements of CAA section 

182(b)(1), moderate CO areas with a design value less than 12.7 ppm, PM2.5 areas, PM10 areas and NO2 areas. In 

ozone areas classified moderate or higher, serious CO, and moderate CO areas with a design value greater than 12.7 

ppm, both interim emissions tests must be met under 40 CFR 93.119. 

9 Assuming neither has elected to shorten the timeframe of the conformity determination (40 CFR 93.106(d)).
21 

estimate emissions from the donut area as decided through interagency consultation. See 

Section 1.6 for details.

• The emissions model to be used for the interim emissions test(s), in the case where there 

is more than one emissions model that could be used (e.g., during a new model grace 

period) (40 CFR 93.111). 

In addition, the MPOs involved in the conformity determination(s) for the nonattainment area 

should discuss the planning assumptions they will use in the regional emissions analysis and the 

sources of that information. The conformity regulation at 40 CFR 93.105(c)(1)(i) specifically 

requires that planning assumptions be discussed in the interagency consultation process. Where 

feasible and appropriate, MPOs (and where applicable, state DOTs) should use consistent 

planning assumptions for the regional emissions analysis in their jurisdictions. 

2.6 If one MPO in the area can meet the requirements of 40 CFR 93.119, 

but another MPO or a donut area cannot, can the MPO that meets the 

requirements show that its transportation plan and TIP conform and 

proceed?

No. Before a multi-jurisdictional nonattainment area has budgets, conformity must be 

demonstrated for the nonattainment area as a whole in order to meet CAA section 176(c)(1) 

requirements that transportation activities will not:

• cause or contribute to a new air quality violation(s); 

• increase the frequency or severity of any existing violation of any standard in any area; or

• delay timely attainment of the NAAQS or any required interim milestones.

It is necessary to estimate emissions from the entire nonattainment area in all transportation 

plan/TIP conformity determinations and the supporting regional emissions analysis because 

separate budgets are not available. For example, in Figure 2.1 below, there are two MPOs: West 

MPO and East MPO. 

 

 
22 

If they choose to model their emissions separately and West MPO appears to pass the applicable 

test(s) of 40 CFR 93.119 but East MPO does not, West MPO cannot proceed to determine 

conformity alone. Since East MPO does not pass the test, it is not known for certain that West 

MPO’s transportation plan and TIP will not cause a new violation, worsen an existing violation, 

or delay timely attainment in the nonattainment area. Therefore, the nonattainment area as a 

whole in this example, cannot demonstrate that transportation activities will not worsen air 

quality or will not delay timely attainment. 

To resolve this situation, East and West MPOs would consult on what options are available for 

demonstrating conformity, including the option to add or model their emissions together to see if 

they pass the applicable regional emissions test(s).
23 

Section 3: Conformity Determinations and Regional Emissions 

Analyses with SIP Budgets for the Relevant NAAQS 

General

3.1 What does this section of the guidance cover? 

Section 3 of this guidance applies to areas designated nonattainment or maintenance for a 

NAAQS that have an adequate or approved budget for that NAAQS (the relevant NAAQS). 

3.2 How do nonattainment and maintenance areas determine conformity 

for a given NAAQS once budgets are available for that NAAQS?

CAA section 176(c)(1) states that federal activities must conform to the SIP. Once a SIP with 

budgets has been submitted and EPA finds those budgets adequate or approves the SIP, the 

budget test using these budgets must be used for conformity according to 40 CFR 93.109(c)(1) 

and 93.118. For example, once a 2006 PM2.5 NAAQS area has budgets for the 2006 PM2.5

NAAQS, it would use those budgets for the budget test as the regional test of conformity for the 

2006 PM2.5 NAAQS. 

EPA’s adequacy finding or approval means that the SIP’s budgets are an appropriate measure for 

whether transportation activities conform due to many factors, including: 

• The budgets are identified and precisely quantified; 

• The budgets are consistent with the SIP’s purpose of reasonable further progress (RFP), 

attainment, or maintenance of a NAAQS; and

• The budgets are consistent with and clearly related to the emissions inventory and the 

control measures in the SIP.10

For a listing of SIP submissions with budgets that are currently under EPA adequacy review or 

that EPA has found adequate or inadequate for conformity purposes, please visit the EPA’s 

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

 

10 There are other criteria that budgets must meet for EPA to find them adequate; for the full list of adequacy criteria, 

see 40 CFR 93.118(e)(4).
24 

3.3 What geographic areas might budgets from a SIP cover, and how is 

conformity generally determined in multi-jurisdictional areas with 

budgets?

State and local agencies can develop SIPs in many different ways. In a multi-jurisdictional

nonattainment or maintenance area located entirely within one state, the state air agency may 

develop a SIP that establishes either:

• Budgets that cover the entire nonattainment or maintenance area, or 

• Subarea budgets that cover each MPO or county (or donut area) within the nonattainment 

or maintenance area.

In a multi-state nonattainment or maintenance area, the state air agencies may decide to establish 

SIPs that contain either:

• Identical budgets that cover the entire nonattainment or maintenance area, or

• Unique budgets that cover only each state’s portion of the nonattainment or maintenance 

area.

The conformity rule at 40 CFR 93.124(d) describes how conformity requirements are met in 

multi-jurisdictional areas: 

“If a nonattainment area includes more than one MPO, the 

implementation plan may establish motor vehicle emissions 

budgets for each MPO, or else the MPOs must collectively make a 

conformity determination for the entire area.”

Once budgets have been found adequate or the SIP containing budgets is approved, the 

conformity determination(s) and regional emissions analysis are done for the geographic area 

that is addressed by the budgets in the SIP. This general principle applies in all situations, 

although there is flexibility for developing the regional emissions analysis and coordinating 

conformity determinations, when several MPOs are involved. Table 3.1 summarizes the general 

situations. 
25 

Summary Table 3.1: How SIPs Affect Geographic Areas Considered in 

Transportation Conformity

For a nonattainment 

or maintenance area 

located:

Where SIP budgets 

are established for:

The geographic area 

considered in 

regional emissions 

analyses is:

The geographic area 

considered in final 

conformity 

determination(s) is:

Within one state The entire area The entire area* The entire area**

Within one state Subareas Each subarea Each subarea

In multiple states The entire area The entire area* The entire area**

In multiple states Each state Each state Each state

* There is flexibility in how the regional emissions analysis is conducted when there is more 

than one MPO. See Section 3.4 for details.

** There may be more than one transportation plan/TIP conformity determination in a 

nonattainment or maintenance area because there may be more than one MPO making 

conformity determinations for separate transportation plans and TIPs. There is flexibility in how 

these conformity determinations are coordinated. See Section 3.4 for details.

The questions and answers that follow in this section provide further detail on the different 

circumstances that can occur.
26 

Nonattainment or Maintenance Areas Located in One State, Where Budgets 

Are Established for the Entire Area

3.4 How is conformity demonstrated when budgets are established for an 

entire nonattainment or maintenance area that is within one state?

This section explains how conformity is demonstrated in a nonattainment or maintenance area 

that is located in a single state, where the SIP establishes one budget for the entire area and there 

is more than one MPO responsible for transportation planning in the area and/or there is a donut 

area.

3.4.1 More than One MPO

When budgets are established for the nonattainment or maintenance area as a whole, and there is 

more than one MPO, the MPOs would complete their respective transportation plan/TIP 

conformity determinations and submit them to DOT, as explained below. Once all conformity 

determinations for a given area are received, DOT would make its conformity determinations at 

the same time. The MPOs must collectively develop a regional emissions analysis for the entire 

area that meets the requirements of 40 CFR 93.118 and 93.122 that would accompany all 

transportation plan/TIP conformity determinations. For example, all MPOs would have to use 

the same analysis years for the regional emissions analysis. Each MPO would show conformity 

of its transportation plan and TIP using the regional emissions analysis done for the entire area. 

The MPOs can develop the regional emissions analysis for the area in either one of two ways:

1. Each MPO can model emissions for its geographic part of the nonattainment or 

maintenance area separately. For each analysis year, the emissions estimated by each 

MPO would be summed together and compared to the area’s applicable budgets. The 

MPOs must all use the same analysis years when completing the budget test, in 

accordance with 40 CFR 93.118. 

2. The MPOs could also work together to model the entire nonattainment or maintenance 

area as a whole at the same time. In this case, 40 CFR 93.118 requirements would be met 

if estimated emissions in each analysis year are less than or equal to the area’s applicable 

budgets. 

3.4.2 One or More MPOs and a Donut Area

If there is one MPO in the nonattainment or maintenance area conducting a conformity 

determination, the MPO must include the emissions estimated from the donut area’s existing and 

proposed transportation system in the regional emissions analysis for the transportation plan and 

TIP conformity determinations (40 CFR 93.118(d)). However, either the MPO or the state DOT 

could estimate emissions from the donut area as decided through interagency consultation. See 

Section 1.6 for details. 
27 

If there is more than one MPO as well as a donut area in a nonattainment or maintenance area, 

the MPOs must work together and with the state DOT or other donut area agency as appropriate 

to create one regional emissions analysis for the entire area that would accompany all 

transportation plan/TIP conformity determinations (40 CFR 93.124(d)). The regional emissions 

analysis would include estimated emissions associated with the transportation plan and TIP as 

well as emissions associated with the donut area(s), if any. The emissions estimated from the 

entire area must be less than or equal to the budget(s) established for the entire area (40 CFR 

93.118). The interagency consultation process would be used to coordinate the analysis years 

when several agencies are completing regional emissions analyses, because the same analysis 

years must be used. 

If a project-level conformity determination is required for a new project in a donut area, the 

project would first need to be included in the associated MPO’s transportation plan and TIP’s 

conformity determination (including the regional emissions analysis) before the project-level 

conformity determination can proceed. For each MPO, there must be a currently conforming 

transportation plan and TIP that meet the MPO’s subarea budgets at the time of any project 

approval,11 and for each MPO, only one conforming transportation plan or TIP (and regional 

emissions analysis) may exist at any time (40 CFR 93.114).12 See Section 3.7 for when a donut 

area can operate independently from an adjacent MPO(s) for project approvals. 

3.4.3 Coordinating Transportation Plan and TIP Update and Amendment Cycles among MPOs

When budgets are established for the entire area and where one MPO updates or amends its 

transportation plan and TIP with a non-exempt project, a DOT conformity determination must be 

made at the same time for all MPO transportation plans and TIPs in that nonattainment or 

maintenance area. This is the case even though the other MPOs in the area may not be updating 

or amending their respective transportation plans or TIPs (40 CFR 93.124(d)). Therefore, MPOs 

in this situation may want to coordinate their transportation plan and TIP update cycles and the 

timeframe of their transportation plans:

• Updated transportation plans and TIPs or amendments that include non-exempt projects 

require a new conformity determination and may require a new regional emissions 

analysis (see 40 CFR 93.104 and 93.122(g)). Where one of the MPOs in the area wants 

to update its transportation plan or TIP or make an amendment that includes one or more 

non-exempt projects, the other MPOs can rely on their portion of a previous regional 

emissions analysis for the conformity determination provided that they meet the criteria 

in 40 CFR 93.122(g).13 Coordination of transportation plan and TIP update and 

 

11 Except during the lapse grace period, where a project could come from the most recent conforming transportation 

plan and TIP (or regional emissions analysis). Refer to Section 3.6.2.

12 As described in Section 2.4.2, EPA believes that there are no other options available before donut area projects 

can proceed in cases where an MPO’s transportation plan and TIP conformity determination and regional emissions 

analysis covers a donut area. Separate regional emissions analyses for donut areas would be inconsistent with 40 

CFR 93.114. 

13 This provision allows a conformity determination to be made without a new regional emissions analysis if the 

previous regional emissions analysis still applies. Please refer to 40 CFR 93.122(g) for more information.
28 

amendment cycles among MPOs in the same nonattainment or maintenance area may 

minimize the number of new regional emissions analyses and conformity determinations 

that have to be completed. 

• Where one of the MPOs in the multi-jurisdictional area wants to update its transportation 

plan and TIP or make an amendment that includes one or more non-exempt projects, the 

public involvement requirements of 40 CFR 93.105(e) of the conformity rule would 

apply for all MPOs, including a public comment period on all MPO transportation 

plan/TIP conformity determinations. However, the requirements under DOT’s 

transportation planning requirements (23 CFR 450.316(b)) would not apply in this 

situation (including the requirement to hold a public hearing) for any MPOs that are not 

updating or amending their transportation plans and TIPs. 

• MPOs may have to analyze additional years if the timeframes of their conformity 

determinations differ. According to 40 CFR 93.118(d)(2), an analysis must be performed 

for the last year of the timeframe of the conformity determination (generally, the last year 

of the transportation plan’s forecast period). 14 For example, in a nonattainment area in 

which one MPO’s transportation plan ends in 2035 and another MPO’s transportation 

plan ends in 2040, both years would have to be analyzed in the regional emissions 

analysis for the entire nonattainment area. Coordination of the transportation plan 

lengths or timeframe for the conformity determinations may minimize the number of 

analysis years that have to be examined in any one regional emissions analysis. 

Nonattainment or Maintenance Areas Located in One State, Where the SIP 

Establishes Subarea Budgets

3.5 How is conformity demonstrated when there is more than one MPO in a 

single state and the SIP establishes subarea budgets for each MPO?

When subarea budgets are created for each MPO, the sum of the subarea budgets equals the total 

amount of emissions the area can have from the on-road mobile source sector and still meet the 

CAA purpose of the SIP for reasonable further progress, attainment, or maintenance. Therefore, 

if each MPO meets its subarea budget(s) for a pollutant and NAAQS in accordance with 40 CFR 

93.118, then the entire area meets the SIP’s purpose for that pollutant and NAAQS. As EPA 

noted in the January 11, 1993 conformity proposal: 

“subarea budgets provide additional assurance that through future 

conformity determinations transportation plans and TIPs will 

produce emission patterns that will achieve attainment.” (58 FR 

3780) 

 

14 The timeframe of a conformity determination could be shortened per 40 CFR 93.106(d).
29 

When the SIP for an area establishes subarea budgets for conformity purposes, these subarea 

budgets must be met for transportation plans and TIPs in the area to conform, as required by 40 

CFR 93.124(c): 

“If the applicable implementation plan (or implementation plan 

submission) estimates future emissions by geographic subarea of 

the nonattainment area, the MPO and DOT are not required to 

consider this to establish subarea budgets, unless the applicable 

implementation plan (or implementation plan submission) 

explicitly indicates an intent to create such subarea budgets for the 

purposes of conformity.” 

The MPOs can make independent conformity determinations for their transportation plans and 

TIPs as long as all of the other subareas in the nonattainment or maintenance area have 

conforming transportation plans and TIPs in place at the time of each MPO’s and DOT’s 

conformity determination. The preamble to the November 24, 1993 conformity final rule 

explains this as follows:

“The SIP may specify emissions budgets for subareas of the 

region, provided that the SIP includes a demonstration that the 

subregional emissions budget, when combined with all other 

portions of the emissions inventory, will result in attainment and/or 

maintenance of the standard. The conformity determination must 

demonstrate consistency with each subregional emissions budget 

in the SIP” (58 FR 62196). 

Thus, when any subarea demonstrates conformity, all subareas within the nonattainment area 

must have conforming transportation plans and TIPs. 

For example, suppose the subarea budgets in a SIP have been found adequate, and one of the 

MPOs for the nonattainment area needs to update its TIP. That MPO can demonstrate 

conformity using its subarea budgets without waiting for the other MPOs in the nonattainment 

area to demonstrate conformity using their subarea budgets, as long as the other MPOs have 

conforming transportation plans and TIPs in place, even if these transportation plans and TIPs 

were previously found to conform using the interim emissions test(s).

The SIP must specifically state that it creates subarea budgets. County-by-county emissions 

projections in a SIP inventory are not subarea budgets unless they are specifically labeled as 

such. If county level emissions projections are included in a SIP but not explicitly defined as 

subarea budgets for the purposes of conformity, the SIP is considered to have budgets for the 

entire area and MPOs must work together to have transportation plan/TIP conformity 

determinations for the entire nonattainment or maintenance area approved by DOT at the same 

time, as described in Sections 3.4, 3.9, 4.8, 4.11, 4.13 and 4.18. 

If MPOs within one nonattainment or maintenance area would prefer to have subarea budgets, 

they would need to communicate their preference to the state and local air agencies during the 
30 

development of the SIP. The conformity rule at 40 CFR 93.105 requires interagency 

consultation on the development of SIPs, as well as transportation plans, TIPs and conformity 

determinations.

3.6 Can an MPO that has its own subarea budgets determine conformity of 

its transportation plan and/or TIP when another MPO in the same area 

is in a conformity lapse or conformity lapse grace period? 

3.6.1 Conformity Lapse

CAA section 176(c) clearly states that conformity applies in nonattainment and maintenance 

areas, rather than individual metropolitan planning areas. Section 176(c) also states that the 

federal government and MPOs cannot approve transportation activities unless they conform to 

the SIP and its budgets. Therefore, in a nonattainment or maintenance area with more than one 

MPO, all MPOs must conform even if the SIP has established subarea budgets. 

If an individual MPO’s transportation plan lapses, it has not demonstrated that it can conform to 

its subarea budget(s). Therefore, there is no way for the other MPOs in the same area to know 

whether their transportation plans and TIPs are consistent with the SIP either. Using Figure 3.2 

below as an example, if East MPO is in a conformity lapse, it cannot be assured that West 

MPO’s transportation activities will meet the purpose of the SIP, even if West MPO meets its 

subarea budgets. 

That is, it is unknown whether the total amount of emissions in the area from the planned 

transportation sector would still meet the CAA requirements of the SIP,because East MPO 

cannot meet its subarea budgets. When one subarea lapses, there is no way for the other MPO to 

show that their planned transportation activities would conform to the SIP for the whole area 

until the lapse is resolved.

If conformity lapses for one MPO’s subarea, the other MPO(s) in the area can continue to 

implement projects in their currently conforming transportation plans and TIPs, but they cannot 

make new transportation plan and TIP conformity determinations until a conformity 
31 

determination has been made for the subarea that is in a conformity lapse. In other words, if the 

conformity status of one subarea lapses, the existing conforming transportation plan and TIPs in 

other subareas continue to be valid, but they cannot adopt new transportation plans, TIPs, or 

plan/TIP amendments that contain non-exempt projects. Therefore, the MPOs should work to 

resolve the lapse in one subarea before the other subareas need to make new transportation 

plan/TIP conformity determinations. 

3.6.2 Conformity Lapse Grace Period

CAA Section 176(c)(9) and 40 CFR 93.104(f) provide a 12-month grace period before a 

conformity lapse occurs in certain situations. During the lapse grace period, a conformity lapse 

has not yet occurred. Therefore, if one MPO in a multi-MPO area with subarea budgets enters a 

lapse grace period, the other MPOs that are not in the lapse grace period can proceed with 

additional conformity determinations for their transportation plans, TIPs, and projects as long as 

conformity requirements in those MPOs are met. 

For the MPO that is in the conformity lapse grace period, project-level conformity 

determinations can continue to be made. The regulation at 40 CFR 93.104(f) allows projects to 

be found to conform during the lapse grace period as long as they were included in either the 

currently conforming transportation plan and TIP (or regional emissions analysis) or the most 

recent conforming transportation plan and TIP (or regional emissions analysis) and other projectlevel conformity requirements are met. However, if an MPO’s TIP has expired, that MPO could 

not meet DOT’s transportation planning requirements. See 73 FR 4423-4424 (January 24, 2008) 

for additional details about the conformity lapse grace period. 

If an MPO in a multi-MPO area enters the one-year conformity lapse grace period and does not 

make a transportation plan and TIP conformity determination by the end of the one year, 

conformity for that MPO would lapse, and all other MPOs would also be affected. Refer to 

Section 3.6.1 above for information in this situation. 

3.7 Can a subarea budget be established for a donut area?

Yes. While the subarea budget provisions of the conformity rule at 40 CFR 93.124(c) and (d) 

specifically address MPOs, the conformity rule does not explicitly prohibit donut areas from 

having subarea budgets. Therefore, EPA has determined that subarea budgets may be 

established for donut areas. 

If this option is chosen, in addition to the MPO(s) determining conformity to their respective 

transportation plans and TIPs every four years, the interagency consultation process must ensure 

that conformity is demonstrated to any subarea budget for a donut area at least every four years 

as well. In the event that an MPO or donut area cannot demonstrate conformity on a four-year 

cycle, the other subareas may not complete a conformity determination until all subareas 

conform. Note that donut areas are not isolated rural areas. Therefore, conformity for donut 

areas must be determined according to the frequency requirements in 40 CFR 93.104. 
32 

3.8 If a SIP establishes only subarea budgets, do MPOs have the option to 

use either an area-wide SIP budget or subarea budgets?

No, not unless the SIP establishes both an overall area budget and subarea budgets, and the SIP 

specifically allows either the area-wide budget or subarea budgets to be used for conformity 

purposes. Specifically, the SIP would need to explicitly state which budget or budgets the MPOs 

would initially use and what must occur if the MPOs want to switch to the other type of 

budget(s). Further, the SIP must clearly explain this flexibility and provide a clear process for 

implementing it. 

MPOs will have to make the switch in a way that meets the conformity rule’s requirements under 

40 CFR 93.124. That is: 

• If the MPOs want to switch to using the area-wide budget, the MPOs must all agree to do 

so and from that point forward, they must make conformity determinations collectively. 

• If the MPOs want to switch to using subarea budgets, then they must all agree, and they 

must all demonstrate conformity to their own subarea budgets at the same time. Once 

that occurs and DOT makes its conformity determination on all the MPO transportation 

plans and TIPs, the MPOs may act separately again.

For more information about establishing both area-wide and subarea budgets, please contact the 

EPA regional office. See Section 1.2 for contact information. 

Multi-State Nonattainment or Maintenance Areas

3.9 How do multi-state nonattainment and maintenance areas determine 

conformity if each state submits a SIP that contains the same budgets 

for the entire multi-state area?

If a multi-state area has a SIP that contains budgets for the multi-state area as a whole, one 

regional emissions analysis would be completed for the entire area using the budget test, 

according to the requirements in 40 CFR 93.118. 

• If just one MPO is involved as in Figure 3.3 below, it would complete the regional 

emissions analysis for the entire multi-state area and submit it to DOT with its 

transportation plan and TIP conformity determination.

• If more than one MPO is involved, the MPOs must collectively develop a regional 

emissions analysis for the entire area that meets the requirements of 40 CFR 93.118 and 

93.122 that would accompany all transportation plan and TIP conformity determinations. 

Once all determinations for a given area are submitted, DOT would make its conformity 

determinations at the same time. In the second case, all MPOs would have to use the same 
33 

analysis years for the regional emissions analysis. Each MPO would show conformity of its 

transportation plan and TIP using the regional emissions analysis done for the entire area. 

For example, in Figure 3.3 below, suppose there is one budget for the multi-state area, but each 

state has its own MPO. 

In this case, one regional emissions analysis would be made for the entire area and the 

conformity determinations for each MPO’s transportation plan and TIP within the area would be 

based on this regional emissions analysis. Any donut area emissions would also be included in 

the regional emissions analysis for the area. DOT would not make its conformity determinations 

for the transportation plans and TIPs until it receives the conformity determinations from all of 

the MPOs in the area. This is similar to single state areas with SIP budgets that cover the entire 

nonattainment or maintenance area. See Sections 3.4, 4.8, 4.11, 4.13, and 4.18 for further 

information. 

3.10 When would it be likely for state air agencies in a multi-state 

nonattainment or maintenance area to submit SIPs with budgets that 

apply to the entire area?

This option would most likely be chosen in areas where there is one MPO responsible for 

transportation planning of the entire multi-state nonattainment or maintenance area. However, 

the option is available to any multi-state nonattainment or maintenance area. In areas with more 

than one MPO, additional coordination would be necessary for transportation plan and TIP 

conformity determinations and the regional emissions analysis because they would need to cover 

the entire nonattainment or maintenance area pursuant to 40 CFR 93.118 and 93.124(d). 
34 

3.11 How is conformity determined for multi-state nonattainment or 

maintenance areas when each state has a SIP that contains budgets only 

for its own state’s portion of the area?

States in a multi-state area have the option of submitting SIPs with budgets for just their own 

portion of the area that, when taken together, meet the applicable CAA requirement. Where 

states have done so and EPA has found such budgets adequate or approved the SIP containing 

the budgets, the MPO or MPOs in each state with such budgets can determine conformity 

completely independently of the other states.15 

EPA concluded that states can operate independently for conformity because the CAA refers to 

conformity to a SIP. Each state’s RFP plan, attainment demonstration, or maintenance plan 

includes inventories, control measures and programs, and budgets that apply to only that state’s 

portion of the nonattainment or maintenance area. 

3.12 How is conformity determined for a multi-state nonattainment or 

maintenance areas when one state has a budget for a NAAQS and the 

other state(s) does not have budgets for that pollutant?

A SIP budget must be used for conformity once EPA finds the budget adequate or approves the 

SIP. Consistent with CAA section 176(c), once a state in a multi-state nonattainment or 

maintenance area has an adequate or approved budget, it can determine conformity completely 

independently of the other states. This is the case even if it is the only state in the nonattainment 

or maintenance area that has such a budget. 

If the area is a two-state area, and one state has a budget(s), then MPOs (with any applicable 

donut areas) in both states can determine conformity on their own: 

• The MPO(s) in the state with the budget(s) would use it to determine conformity for the 

area covered by the budget; 

• The MPO in the state without a budget(s) would use the interim emissions test(s), as 

applicable (see 40 CFR 93.119) for that state’s portion of the area. 

However, if the multi-state area is a three-state area and only one state has a budget(s), only the 

MPO(s) in the state with the budget(s) could determine conformity on its own. The MPOs in the 

other two states would determine conformity for that NAAQS together, using the interim 

emissions test(s).

 

15 For example, this is the case even when one state has a maintenance plan for a NAAQS and the other state(s) have 

budgets for another type of SIP for that pollutant.
35 

Section 4: Conformity Determinations and Regional Emissions 

Analyses with SIP Budgets for Another NAAQS of the Same 

Pollutant 

4.1 To what areas does this section of the guidance apply? 

This section of the guidance applies to areas that are determining conformity for a relevant 

NAAQS that do not have a budget for that NAAQS but have a budget for another NAAQS of the 

same pollutant (another NAAQS).

16 Conformity tests for these areas are covered by 40 CFR 

93.109(c)(2). 

For example, an area designated nonattainment for the 2006 PM2.5 NAAQS that does not have 

adequate or approved budgets for that NAAQS but has budgets for the 1997 PM2.5 NAAQS

would be covered by this section of the guidance. 

Once the area submits a SIP that contains a budget for the NAAQS for which it is designated 

nonattainment and for which conformity requirements apply (relevant NAAQS), and EPA finds 

the budget adequate or approves the SIP that contains it, the area must use it for conformity for 

that NAAQS (40 CFR 93.109(c)). When that occurs, this section of the guidance no longer

applies; readers should consult Section 3 of this guidance. 

General

4.2 What scenarios could result when determining conformity for a 

NAAQS using a budget from another NAAQS of the same pollutant? 

As described in the Conformity Restructuring rule (77 FR 14979), there are four generic 

scenarios for how an area’s boundaries for the relevant NAAQS relate to boundaries covered by 

budgets for another NAAQS of the same pollutant. The conformity rule is written with these 

four scenarios in mind. 

To determine which scenario describes an area, it is necessary to consider the boundary of the 

entire area designated for the relevant NAAQS. For example, in a multi-state 2006 PM2.5 area, 

the 2006 PM2.5 area nonattainment boundary refers to the entire multi-state area, rather than each 

state’s individual portion. 

Figure 4.1 below illustrates the four generic boundary scenarios. 

 

16 A precursor budget for one pollutant cannot be used as the test of conformity for any other pollutant. If, for 

example, an area has an approved 1997 ozone attainment demonstration with a NOx budget, this NOx budget must 

be used to demonstrate conformity for the 1997 ozone NAAQS and would also be used to demonstrate conformity 

for any future ozone NAAQS before the area has a budget for it. However, this ozone SIP NOx budget could not be 

used to demonstrate conformity for a PM or NO2 NAAQS because doing so would not be consistent with the Clean 

Air Act. See the Conformity Restructuring rule (77 FR 14979) for details.
36 

Figure 4.1: The Four Boundary Scenarios

 Scenario 1 Scenario 2 Scenario 3 Scenario 4

= Another NAAQS area for the same pollutant 

 

= Relevant NAAQS area (i.e., for which conformity applies) 

• Scenario 1: Boundaries for both areas are identical. 

• Scenario 2: The boundary of the relevant NAAQS area is smaller than and 

completely within the area designated for another NAAQS of the same pollutant. 

• Scenario 3: The boundary of the relevant NAAQS area is larger than and contains the 

area designated for another NAAQS of the same pollutant. 

• Scenario 4: The boundary of the relevant NAAQS area overlaps with a portion of the 

area designated for another NAAQS of the same pollutant. 

It is possible that, in any scenario, the boundary of the relevant NAAQS could include portions 

of one or more areas designated for another NAAQS. For example, a Scenario 1 area could be 

formed from two areas designated for another NAAQS. In these cases, the interagency 

consultation process should be used to determine how the budgets from another NAAQS will 

apply. The information below covers further details on all of the scenarios. 

4.3 What are the general test requirements for regional emissions analyses 

for these areas?

In general, if an area does not have budgets for the relevant NAAQS but has budgets from 

another NAAQS of the same pollutant, these budgets must be used in the budget test. Where 

such budgets do not cover the entire area, the interim emissions test(s) may also have to be used 

(40 CFR 93.109(c)(2)). 

A 2006 court decision established the legal parameters for using existing budgets as the regional 

conformity test (Environmental Defense v. EPA, 467 F.3d 1329 (DC Cir. 2006)). EPA 

incorporated the court’s decision for ozone conformity tests in its January 24, 2008 final rule (73 

FR 4424). While the court’s decision concerned ozone, EPA believes the court’s holding is 

relevant for other pollutants for which conformity must be demonstrated. Therefore, EPA 
37 

incorporated the court’s decision regarding conformity tests in its March 24, 2010 final rule (the 

“PM Amendments” rule, 75 FR 14260). Most recently, in its Conformity Restructuring rule (77 

FR 14979), EPA reorganized 40 CFR 93.109(c) so that the court’s decision is incorporated in the 

regulation for all NAAQS for which conformity applies. 

This requirement also applies when areas have subarea budgets for another NAAQS of the same 

pollutant. Where subarea budgets exist for another NAAQS, MPOs must use them to 

demonstrate conformity for the relevant NAAQS until they have budgets for the relevant

NAAQS. In general, each subarea can determine conformity independently as long as they are

using subarea budgets for another NAAQS and other applicable tests to determine conformity. 

See Section 4.14 for details. See also Section 3 of this guidance for further information on 

conformity determinations using subarea budgets. 

4.4 How is the budget test generally implemented in areas that do not have 

a budget for the relevant NAAQS but have a budget for another 

NAAQS of the same pollutant?

The budget test requirements in 40 CFR 93.118 for relevant NAAQS areas with a budget for 

another NAAQS of the same pollutant will generally be implemented in the same manner as the 

budget test for another NAAQS. First, as described above, the geographic area covered by the 

relevant NAAQS may be different than that covered by the other NAAQS of the same pollutant 

in some cases. Second, the years for which the regional emissions analysis is required (i.e., 

analysis years) may differ. 

Areas that use budgets from another NAAQS for their relevant NAAQS conformity 

determinations will need to determine the modeling analysis years that apply for the relevant 

NAAQS per 40 CFR 93.118(d)(2). Under this section, a regional emissions analysis for the 

budget test must be performed for: 

• the attainment year, if it is within the timeframe of the transportation plan and 

conformity determination, 

• the last year of the timeframe of the conformity determination, and 

• intermediate years as necessary, such that analysis years are no more than ten years 

apart.

The attainment year analysis is to be for an area’s attainment year for the relevant NAAQS, and 

not the attainment year for the other NAAQS of the same pollutant. The area must calculate 

emissions in the analysis years from the planned transportation system, and compare them to the 

budget. Emissions projected for each analysis year must be within the budget for the most recent 

prior year. Interpolation can be used between analysis years for demonstrating consistency with 

budgets. Refer to 40 CFR 93.118 for specific details. 

For example, consider an area designated nonattainment for the 2006 PM2.5 NAAQS which has 

an attainment year of 2014. The boundary for the 2006 PM2.5 area and the 1997 PM2.5 area are 

exactly the same (a Scenario 1 area), and 1997 annual PM2.5 budgets cover all of the 2006 24-

hour PM2.5 area. The 1997 PM2.5 budgets are for the years 2009 and 2014 (the RFP year and the 
38 

attainment year, respectively.) This 2006 PM2.5 area must use the 1997 PM2.5 budgets to 

determine conformity for the 2006 PM2.5 NAAQS. 

Suppose the 2006 PM2.5 NAAQS area is demonstrating conformity in the year 2012 for a 

transportation plan that covers the years 2012 through 2035 and has not elected to shorten the 

timeframe of the conformity determination per 40 CFR 93.106(d)(2). This area would examine 

the following analysis years in its 2006 PM2.5 NAAQS conformity determination: 

• 2014, which fulfills the 40 CFR 93.118(d)(2) requirement to analyze the 2006 PM2.5

attainment year,

• 2020 and 2030, which fulfills the 40 CFR 93.118(d)(2) requirement to analyze an 

intermediate year so that analysis years are no more than 10 years apart; and

• 2035, which fulfills the requirement in 40 CFR 93.118(d)(2) requirement to analyze the 

last year of the transportation plan/timeframe of the conformity determination.

In addition, the conformity rule at 40 CFR 93.111(b) requires that the 2006 PM2.5 area must also 

demonstrate consistency with the 1997 PM2.5 budgets for the year 2014. Note that, in this 

example, because there is no analysis year required prior to 2014 and the year 2009 is no longer 

within the timeframe of the conformity determination, the budget for 2009 does not need to be 

assessed. 

In the example, the budget test would then be satisfied as follows: 

• 2014: budget test, using the 2014 budgets 

• 2020: budget test, using the 2014 budgets 

• 2030: budget test, using the 2014 budgets 

• 2035: budget test, using the 2014 budgets 

EPA notes that under 40 CFR 93.118(d)(2), interpolating between analysis years can be used to 

demonstrate consistency with budgets in some cases. However, this was not necessary in this 

example. 

As stated earlier, once adequate or approved budgets are established for the 2006 PM2.5 NAAQS, 

the budget test would be completed using only those budgets, rather than budgets for the 1997 

PM2.5 NAAQS.

Note there can be limited cases where an area has a budget for another NAAQS of the same 

pollutant that cannot be used for all analysis years because it is established for a later year. 

When this occurs, the interim emissions test(s) would have to be used for analysis years that are 

earlier than the budget year. For example, suppose there is a 2008 ozone NAAQS area that is a 

Scenario 1 area. This area has 1997 ozone NAAQS maintenance budgets for the year 2022, and 

that is the only year for which ozone budgets exist. In this case, the 2008 ozone area must use 

the budget test according to 40 CFR 93.118 for 2022 and later years, and the interim emissions 

test(s) according to 40 CFR 93.119 for analysis years earlier than 2022. The EPA regional office 

is available to discuss what analysis years apply in different situations. See contact information 

in Section 1.2. 
39 

4.5 Where relevant NAAQS areas have to use both the budget test and the 

interim emissions test(s), what analysis years must be chosen? 

As described in the March 24, 2010 and July 1, 2004 final rules (75 FR 14260 and 69 FR 40004, 

respectively), there will be cases in Scenario 3 or 4 areas where both the budget and interim 

emissions tests are used.17 In cases where both the budget and interim emissions tests are used, 

the interagency consultation process can be used to choose analysis years that meet the 

requirements of both 40 CFR 93.118 and 93.119 so that the number of analysis years is 

minimized. 

In the budget test, the years that must be analyzed (40 CFR 93.118(d)(2)) are: 

• the attainment year, if it is within the timeframe of the transportation plan and conformity 

determination,

• the last year of the timeframe of the conformity determination, and

• intermediate years as necessary, such that analysis years are no more than ten years apart.

In the interim emissions tests, the years that must be analyzed (40 CFR 93.119(g)) are: 

• a year no more than five years beyond the year in which the conformity determination is 

being made,

• the last year of the timeframe of the conformity determination, and

• intermediate years as necessary, such that analysis years are no more than ten years apart.

For example, consider an area designated nonattainment and classified as moderate for the 2008 

ozone NAAQS that is larger than and encompasses the area covered by the 1997 ozone budgets 

(i.e., budgets for NOx and VOC). The area’s attainment year for the 2008 ozone NAAQS is 

2018. The 1997 ozone budgets are for the years 2007 and 2009 (the RFP year and the attainment 

year for moderate 1997 ozone areas). Per 40 CFR 93.109(c)(2)(iii)(A), this area is going to use 

both the budget and interim emissions tests to determine conformity for the 2008 ozone 

NAAQS.18 

Suppose this 2008 ozone NAAQS area is demonstrating conformity in the year 2012 for a 

transportation plan that covers the years 2012 through 2035 and has not elected to shorten the 

timeframe of the conformity determination per 40 CFR 93.106(d)(2). This area would examine 

the following analysis years in its 2008 ozone NAAQS conformity determination: 

• 2018, which fulfills the 40 CFR 93.118(d)(2) requirement to analyze the attainment year 

for areas classified moderate under the 2008 ozone NAAQS, 

• 2015 and 2025, which fulfill the 40 CFR 93.119(g) requirement to analyze a year not 

more than five years beyond the year in which the conformity determination is being 

made (2015, in this example), and the requirement in both rule sections to analyze an 

intermediate year so that analysis years are no more than 10 years apart (2015 and 2025 

in this example), and 

 

17See Section 4.2 for details on various boundary scenarios.

18 The conformity rule at 93.109(c)(2)(iii)(B) provides the option to use the budget test as the sole test for 

conformity for a Scenario 3 area; however, the Scenario 3 area in this example will be using both the budget and 

interim emissions tests to determine conformity for the 2008 ozone NAAQS.
40 

• 2035, which fulfills the requirement in both rule sections to analyze the last year of the 

transportation plan/timeframe of the conformity determination.

In addition, the conformity rule requires that the portion of the area covered by the 1997 ozone 

budgets must also demonstrate consistency in the years budgets are established. However, in this 

example, because the years 2007 and 2009 are no longer within the timeframe of the conformity 

determination, and an analysis year is not chosen before 2015, consistency with the budgets for 

2007 and 2009 does not need to be demonstrated. 

In the example, the regional conformity test requirements would then be satisfied as follows: 

• 2015: budget test (using 2014 budgets) and interim emissions tests (40 CFR 

93.119(b)(1)) 

• 2018: budget test (using 2014 budgets) and interim emissions tests (40 CFR 

93.119(b)(1)) 

• 2025: budget test (using 2014 budgets) and interim emissions tests (40 CFR 93.119 

(b)(1)) 

• 2035: budget test (using 2014 budgets) and interim emissions tests (40 CFR 

93.119(b)(1)) 

As described in 40 CFR 93.109(c)(2)(iii)(A), the regional emissions analysis for the budget test 

in this Scenario 3 area example would cover the portion of the nonattainment area covered by the 

1997 ozone budgets. The regional emissions analyses for the interim emissions test(s) in a multistate area would cover the portion of the state’s 2008 ozone area not covered by the 1997 ozone 

budgets. 

As stated earlier, once adequate or approved budgets are established for the 2008 ozone NAAQS, 

the budget test would be completed using only those budgets, rather than by using budgets for 

the 1997 ozone NAAQS and the interim emissions tests. 

4.6 In an area that has subarea budgets for another NAAQS of the same 

pollutant, how should MPOs demonstrate conformity for the first time 

under the relevant NAAQS and for subsequent conformity 

determinations? 

As described in Section 3 of this guidance, when a nonattainment or maintenance area has 

subarea budgets, conformity for an MPO’s transportation plan and TIP can be determined only if 

all other subareas have conforming transportation plans and TIPs in place for a given pollutant 

and NAAQS. This requirement applies also to cases where MPOs are demonstrating conformity 

for the first time using subarea budgets for another NAAQS of the same pollutant. 

In general, EPA and DOT believe it is necessary for the first conformity determination under the 

relevant NAAQS to be performed as follows: each MPO would demonstrate conformity of its 

transportation plan and TIP to the relevant NAAQS using the subarea budgets for another 

NAAQS. All of the MPOs’ transportation plan/TIP conformity determinations would then be 
41 

submitted to DOT. DOT will not make its conformity determination on any of the transportation 

plans or TIPs for the relevant NAAQS until every MPO in the area has made a conformity 

determination for its transportation plan and TIP. Please note that this answer may differ for 

Scenario 3 and 4 areas where an additional portion of the relevant NAAQS area is not covered 

by budgets for another NAAQS. See below for details.

All MPOs must have an initial valid conformity determination for the relevant NAAQS by the 

end of the one-year grace period under 40 CFR 93.102(d). If any do not, DOT will be unable to 

make any conformity determinations for the relevant NAAQS, and all of the MPOs’ 

transportation plans and TIPs in the area will lapse.

In general, once DOT has made its initial conformity determination for the area, the MPOs will 

operate as usual: before any MPO in the area determines conformity, all other MPOs in the area 

must have a conforming transportation plan and TIP in place for the relevant NAAQS. If one 

subarea is in a conformity lapse, conformity determinations for new or revised transportation 

plans and TIPs cannot be made in other subareas until the lapse ends. 

4.7 How would conformity be demonstrated in multi-state areas where each 

state has its own budget for another NAAQS of the same pollutant? 

Where a state has an adequate or approved budget for another NAAQS of the same pollutant for 

its portion of the nonattainment area, the MPOs in the state would determine conformity 

independently from MPOs in the other states, including the initial conformity determination. 

The MPO in that state’s portion of the area must use such budget(s) to demonstrate conformity 

for the relevant NAAQS. 

For example, in the case where a multi-state area is designated nonattainment for the 2006 PM2.5

NAAQS and all the states have adequate or approved 1997 PM2.5 NAAQS budgets for their 

portion of the 2006 PM2.5 area, the MPO(s) in each state can each demonstrate conformity 

independently of the other MPOs in the other states. The MPOs would use 1997 PM2.5 NAAQS 

budgets for the 2006 PM2.5 NAAQS until they have adequate or approved 2006 PM2.5 NAAQS 

budgets. 

In another example of a two-state area, if only one of the states has a budget for another NAAQS 

of the same pollutant, then MPOs in both states can determine conformity independently: 

• The MPO in the state with the budget for another NAAQS would continue to use it for 

the relevant NAAQS; and

• The MPO in the state without such a budget would use the interim emissions test(s).

However, if the area is a three-state area and only one state had budgets from another NAAQS, 

only the MPO in the state with the budgets could determine conformity on its own. MPOs in the 

other two states would determine conformity for the relevant NAAQS together using the interim 

emissions test(s).
42 

If the MPO in one of the states cannot demonstrate conformity at the end of the one-year grace 

period under 40 CFR 93.102(d), the MPO(s) in the other state(s) in the nonattainment area can 

continue to make conformity determinations. This is because, where they have their own SIP 

and budgets, the states operate independently for conformity purposes. 

EPA notes, however, that in Scenario 3 and 4 areas, the circumstances are more complex. In 

those cases, budgets for another NAAQS may not be the sole test of conformity for a state’s 

portion of the relevant NAAQS area since the conformity determination must include a regional 

emissions analysis that includes the entire relevant NAAQS area. See below for how this applies 

to the various boundary scenarios.

See Section 3 of this guidance for further details on conformity determinations using multi-state 

budgets. 

Scenario 1 Areas

As described in Section 4.2, the boundary for the Scenario 1 area designated for the relevant 

NAAQS is identical to the boundary for the area designated for another NAAQS of the same 

pollutant: 

= Another NAAQS area for the same pollutant 

= Relevant NAAQS area (i.e., for which conformity applies) 

Scenario 1

4.8 How is conformity demonstrated in Scenario 1 areas where one budget 

(or one set of budgets) apply for the entire area? 

Conformity determinations are straightforward in Scenario 1 areas, because the area boundaries 

for the relevant NAAQS area and another NAAQS area are exactly the same. Where the area is 

covered by more than one MPO, they must coordinate their transportation plan/TIP conformity 

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

conformity determinations for the relevant NAAQS, DOT will make its conformity 

determinations at the same time. Further, the planning agencies will have to work together to 

develop one regional emissions analysis for the relevant NAAQS per 40 CFR 93.109(c)(2)(i), 

just as they would when determining conformity in the past. See Section 3.4 and 3.9 of this 

guidance for further information regarding how a regional emissions analysis could be completed 

for these areas.
43 

4.9 How is conformity demonstrated in a Scenario 1 area when subarea 

budgets have been established? 

As discussed in Section 3.2 of this guidance, conformity follows the SIP. Therefore, when 

budgets to be used for conformity are subarea budgets from another NAAQS of the same 

pollutant, conformity determinations and the supporting regional emissions analyses for the 

relevant NAAQS area are done using these subarea budgets. See Sections 3.5 through 3.8 for 

additional information. 

4.10 How is conformity demonstrated in multi-state Scenario 1 areas, where 

each state has its own budget?

As discussed in Section 3.3, conformity and the supporting regional emissions analysis are done 

for the geographic area that is covered by the SIP’s budgets, i.e., each state’s portion of the 

nonattainment area.

 

An MPO in a state with a budget for another NAAQS of the same pollutant can determine 

conformity for the relevant NAAQS independent of MPOs in the other states. This is true 

whether the other state or states do not have budgets and must use the interim emissions test(s), 

or the MPOs in the other state or states in the area are in a conformity lapse, or the MPOs in the 

other state or states have not yet determined conformity for the relevant NAAQS. 

Please see Sections 3.11 and 3.12 of this guidance for further information regarding how a 

regional emissions analysis could be completed for these areas.

Scenario 2 Areas

As described in Section 4.2, the boundary for the Scenario 2 area designated for the relevant 

NAAQS is smaller than and completely within the area designated for another NAAQS of the 

same pollutant:

= Another NAAQS area for the same pollutant

= Relevant NAAQS area (i.e., for which conformity applies) 

Scenario 2

 
44 

4.11 How is conformity demonstrated in a Scenario 2 area, when the budget 

applies to the entire area for the relevant NAAQS? 

In a Scenario 2 area, the relevant NAAQS area is smaller than and completely encompassed by 

an area designated for another NAAQS of the same pollutant. In this situation, one of the 

following options must be met for the relevant NAAQS area: 

• The budget test using the subset or portion of the budget for the other NAAQS that 

applies to the relevant NAAQS area, where such portion(s) can be reasonably identified 

(40 CFR 93.109(c)(2)(ii)(A)). 

For example, a three-county area designated for the relevant NAAQS is entirely within a

four-county area that has a budget for another NAAQS, and the SIP identified emissions 

by county. In this case, the portion of that other NAAQS budget that applies to the 

relevant NAAQS area can be identified, so it could be used to demonstrate conformity for 

the relevant NAAQS; 

OR

• The budget test using the budget for another NAAQS of the same pollutant for the entire 

area designated for that other NAAQS. In this case, any additional emissions reductions 

beyond those addressed by control measures in the SIP for that other NAAQS would be 

required to come from the relevant NAAQS area (40 CFR 93.109(c)(2)(ii)(B)). 

For example, in the case of the three-county area, the four-county area’s budget for 

another NAAQS could be used for the four-county area (i.e., the area designated for that 

other NAAQS) to demonstrate conformity for the three-county area (i.e., the relevant 

NAAQS area). Any reductions needed would have to come from within the three-county 

area. 

The interagency consultation process must be used to determine which of these options will be 

used. Through interagency consultation, it can be determined whether using a portion of the 

budgets covered by another NAAQS is feasible and, if so, how deriving such a portion would be 

accomplished. It may be possible to create budgets for only the relevant NAAQS area, for 

example if the budget contains estimates of emissions by county, and emissions from the county 

or counties not included in the relevant NAAQS area can be subtracted. 

Areas that can identify that portion of the budget(s) that applies to the relevant NAAQS area 

could choose to use either option each time they make a conformity determination. For any 

particular conformity determination, however, the same choice would have to be used for each 

analysis year. EPA believes that to do otherwise would be unnecessarily complicated and may 

indicate that one option used consistently for all analysis years would not demonstrate 

conformity. 
45 

The MPO or MPOs must coordinate transportation plan/TIP conformity determinations and 

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

DOT will make its conformity determinations at the same time. 

If it is not possible to determine what portion of the budget for another NAAQS applies to the 

relevant NAAQS area, the MPO or MPOs will have to determine conformity for the area covered 

by the budget for another NAAQS, and if reductions are needed to meet the budgets, they must 

come from within the relevant NAAQS area as required by 40 CFR 93.109(c)(2)(ii)(B).

4.12 How is conformity demonstrated in multi-state Scenario 2 areas, where 

each state has its own budget? 

As discussed in Section 3.3, conformity is determined for the geographic area that is covered by 

the SIP’s budgets, i.e., each state’s portion of the nonattainment area. 

For Scenario 2 areas, the MPO in each state can choose either of two options for the budget test 

for its portion of the relevant NAAQS area: 

• The budget test using the subset or portion of the budget for another NAAQS of the same 

pollutant that covers the relevant NAAQS area within that state, where such portion(s) 

can reasonably be identified (40 CFR 93.109(c)(2)(ii)(A)); 

OR

• The budget test using the budget for another NAAQS of the same pollutant for the entire 

area covered by that budget within the state. In this case, if additional emissions 

reductions are necessary to meet the budget test, these emissions reductions must come 

from within that state’s portion of the relevant NAAQS area (40 CFR 

93.109(c)(2)(ii)(B)). 

Consistent with Section 4.11, the interagency consultation process must be used to determine 

which of these options will be used. 
46 

Scenario 3 Areas 

As described in Section 4.2, the boundary for the Scenario 3 area designated for the relevant 

NAAQS is larger than and contains the area designated for another NAAQS of the same 

pollutant: 

= Another NAAQS area for the same pollutant

= Relevant NAAQS area (i.e., for which conformity applies)

Scenario 3

Scenario 3 Areas within One State

4.13 How is conformity demonstrated in a Scenario 3 area located entirely 

within one state? 

In this case, the nonattainment area for the relevant NAAQS covers a larger geographic area and 

encompasses an entire area for another NAAQS of the same pollutant. In this situation, 

conformity for the relevant NAAQS is determined by meeting either 40 CFR 93.109(c)(2)(iii)(A) 

or (B): 

(A)The budget test using the budgets for another NAAQS of the same pollutant for the 

portion of the relevant NAAQS area that it covers AND the interim emissions test(s) for:

o The remaining portion of the relevant NAAQS area; or

o The entire relevant NAAQS area

OR

(B) The budget test using the budget(s) for another NAAQS of the same pollutant for the 

entire relevant NAAQS area. 

If the MPOs choose an option that requires the use of an interim emissions test, once they select 

a particular interim emissions test and the geographic area it will address, the same test must be 

used consistently for all analysis years. The interagency consultation process must be used to 

determine which analysis years should be selected for regional emissions analyses where the 

budget test and interim emissions tests are used. It may be possible to choose analysis years that 

satisfy both the budget and interim emissions test(s) requirements if both tests are used. See 

Section 4.5 for more information.
47 

If the relevant NAAQS area includes a donut area, the interagency consultation partners must 

decide which agency will be responsible for the donut area regional emissions analysis. See 

Section 1.6 for details.

4.14 How is conformity demonstrated in a Scenario 3 area located entirely 

within one state, when subarea budgets apply? 

As described in Sections 3.5 through 3.8 and in Sections 4.3, 4.6 and 4.9, each MPO can develop 

its own regional emissions analysis and conformity determination for its transportation plan and 

TIP, as long as all of the other MPOs in the area have a conforming transportation plan and TIP 

for the relevant NAAQS in place. The unique aspect in a Scenario 3 area is that there is a 

portion of the relevant NAAQS area that is not covered by the subarea budgets for another 

NAAQS of the same pollutant. For this portion of the relevant NAAQS area, a regional 

emissions analysis using the interim emissions test(s) must be done, and this regional emissions 

analysis can be done for either:

• The part of the relevant NAAQS area not covered by the subarea budgets for another 

NAAQS of the same pollutant, 

OR

• The entire relevant NAAQS area.

As addressed in Section 4.6, for the initial conformity determination under the relevant NAAQS, 

each MPO can determine conformity for its own transportation plan and TIP, including any 

donut portion of the area where applicable, and DOT will make its conformity determination for 

all MPOs at the same time. 

Figure 4.2: A Scenario 3 Area within One State with Subarea Budgets from 

Another NAAQS of the Same Pollutant

 = Another NAAQS area

 

 = Relevant NAAQS area 

A,B,C,D = MPOs with subarea budgets from 

 another NAAQS of the same 

 pollutant 

E = New county in relevant NAAQS area
48 

In Figure 4.2 above, MPOs A, B, C, and D can develop conformity determinations for the 

relevant NAAQS for just their own transportation plans and TIPs using their subarea budgets for 

another NAAQS of the same pollutant. The regional emissions analysis for Part E must be done 

using the interim emissions test(s). Part E may be a donut area or may have its own MPO. If 

Part E is a donut area, the parties involved in interagency consultation must discuss which MPO

will be responsible for Part E’s emissions, and for what geographic area the regional emissions 

analysis will be done (either just Part E, or the entire area A through E). See Sections 1.6 and 3.5 

through 3.8 for details. 

Once an area selects a particular interim emissions test and the geographic area it will address, 

the same test must be used consistently for all analysis years. The consultation process must be 

used to determine which analysis years should be selected for regional emissions analyses where 

the budget test and interim emissions test(s) are used. It may be possible to choose analysis 

years that satisfy both the budget and interim emissions test(s) requirements. See Section 4.5 for 

more information. 

Scenario 3 Multi-State Areas

4.15 How is conformity demonstrated in a multi-state Scenario 3 area, where 

all the states have their own budgets?

As described above, conformity determinations can be made independently in any state that has 

its own budget(s). In addition, there are several options for completing the regional emissions 

analysis if the relevant NAAQS area within a state is larger than the area covered by another 

NAAQS of the same pollutant: 

Option 1: The budget test for each state’s portion of the relevant NAAQS area covered by the 

budget(s) AND the interim emissions test(s) for either:

• the portion of the relevant NAAQS area within that state that is not covered by the 

budget(s), 

• that state’s entire portion of the relevant NAAQS area; or 

• the entire multi-state area for the relevant NAAQS.

For Scenario 3 areas, any of these approaches could be implemented under 40 CFR 

93.109(c)(2)(iii)(A).

Option 2: The budget test for the entire relevant NAAQS area using the budget(s) for another 

NAAQS of the same pollutant (40 CFR 93.109(c)(2)(iii)(B)). 

For example, in Figure 4.3 below, an area designated for a relevant NAAQS includes parts of 

three states, and the boundary in States A and B is unchanged from the area covered by the 

budgets, but the boundary in State C is larger. 
49 

Figure 4.3: A Multi-State Scenario 3 Area

States A, B, and C can continue to determine conformity independently from one another for the 

relevant NAAQS. MPOs in States A and B would determine conformity for their own portions 

of the relevant NAAQS area using their respective budgets for another NAAQS of the same 

pollutant. 

The MPO in State C could choose to determine conformity for its portion of the relevant

NAAQS area as follows:

Option 1: The budget test using the budget(s) for another NAAQS for the geographic area 

covered by such budgets, plus the interim emissions test(s) for either one of the following: 

• the portion of the relevant NAAQS area in State C not covered by budget(s) (white 

portion of Figure 4.3); 

• the entire portion of the relevant NAAQS area that lies within State C (gray and white 

within State C portion of Figure 4.3) ; or

• the entire multi-state relevant NAAQS area (all of Figure 4.3). 

OR 

Option 2: Using its budget(s) for another NAAQS for the budget test, the entire portion of the 

relevant NAAQS area in State C (including that portion of the relevant NAAQS area that lies 

within State C that is not covered by another NAAQS budget). 
50 

4.16 How is the regional emissions analysis done in multi-state Scenario 3 

areas, where only one of the states has its own budget(s)? 

As discussed elsewhere in this guidance, if one state has a budget(s) for another NAAQS of the 

same pollutant and the relevant NAAQS area is comprised of two states, then MPOs in both 

states can determine conformity on their own: 

• The MPOs in the state with the budget would use it to demonstrate conformity for its 

portion of the relevant NAAQS area. 

• The MPOs in the state without a budget would use the interim emissions test(s). 

In Figure 4.4 below, the MPOs in each state can determine conformity for its own portion of the 

relevant NAAQS area, even though State B does not have any budget for that pollutant. 

Figure 4.4: A Two-State Scenario 3 Area 

However, if the relevant NAAQS area is a three-state area and only one state has a budget for 

another NAAQS of the same pollutant, only the MPO in the state with the budget would 

determine conformity on its own. MPOs in the other two states would determine conformity for 

the relevant NAAQS together using the interim emissions test(s). See Section 2 for guidance on 

determining conformity using the interim emissions test(s).

Scenario 3 - General

4.17 What are the special issues that the interagency consultation process 

should consider in Scenario 3 areas?

The interagency consultation process is of key importance in these areas. Because the boundary 

of the relevant NAAQS area is larger than the area covered by the budget(s) for another 

NAAQS, one or more planning agencies previously not involved in conformity may become part 
51 

of the interagency process. These planning agencies need to be included in the decision-making 

process for the area.

Through the interagency consultation process (40 CFR 93.105), the involved parties must decide: 

• whether it is more appropriate for the state DOT or an MPO to prepare the regional 

emissions analysis for a donut area, if there is one; 

• which interim emissions test will be used, in areas that can select only one test; 

• analysis years for the budget test and interim emissions test(s) when both are used. It 

may be possible to choose analysis years that satisfy both the budget and interim 

emissions test requirements in 40 CFR 93.118(d)(2) and 93.119(g); and

• whether the relevant NAAQS area can meet the budget(s) without the interim emission 

test. Scenario 3 areas may be able to demonstrate conformity without an interim 

emissions test if the entire relevant NAAQS area can meet the budget for another 

NAAQS of the same pollutant and if not, what portion of the area the interim emissions 

test(s) will cover. 

Scenario 4 Areas 

As described in Section 4.2, the boundary for the Scenario 4 area designated for the relevant 

NAAQS overlaps with a portion of the area designated for another NAAQS of the same 

pollutant: 

= Another NAAQS area for the same pollutant

= Relevant NAAQS area (i.e., for which conformity applies) 

Scenario 4

Scenario 4 Areas within One State

4.18 How is conformity demonstrated in a Scenario 4 area, when one budget 

applies for the entire area rather than subarea budgets? 

In a Scenario 4 area, the boundaries partially overlap for the relevant NAAQS area and the area

designated by another NAAQS of the same pollutant. Unlike Scenario 3 areas, the relevant

NAAQS area does not contain the entire area designated for another NAAQS. Therefore, the 

budgets cannot be the sole test of conformity for the relevant NAAQS, since a conformity 

determination must include a regional emissions analysis that includes the entire relevant

NAAQS area.
52 

In this scenario, conformity for the relevant NAAQS is determined with the budget test using the 

budgets for another NAAQS for the portion of the relevant NAAQS area that the budget covers, 

AND the interim emissions test(s) for: 

• the remaining portion of the relevant NAAQS area, (i.e., the portion not covered by the 

budgets), 

OR

• the entire relevant NAAQS area (40 CFR 93.109(c)(2)(iv). 

If the relevant NAAQS area includes a donut area, the interagency consultation partners must 

decide which agency will be responsible for the donut area regional emissions analysis. See 

Section 1.6 for details.

Similar to Scenario 3 areas, the same test and geographic portion of the relevant NAAQS area 

must be used consistently for all analysis years. 

For example, in Figure 4.5 below, a relevant NAAQS area partially overlaps an area designated 

nonattainment previously for another NAAQS of the same pollutant. 

Figure 4.5: A Scenario 4 Area within One State

In this example, the conformity determination for the relevant NAAQS area would be completed 

using: 

• The budget test, for that portion of the relevant NAAQS area covered by the budget (as 

indicated by the arrow in Figure 4.5),

AND 

• The interim emissions test for either:
53 

o The part of the relevant NAAQS area not covered by the budget(s) for another 

NAAQS of the same pollutant – in Figure 4.5, the white portion inside the bolded 

circle, 

OR

o The entire relevant NAAQS area (the entire area inside the bolded circle). 

Scenario 4 Multi-State Areas

4.19 How does a multi-state Scenario 4 area determine conformity, when 

each state has its own budget(s)? 

Multi-state Scenario 4 areas are a unique case. Where each state has its own budget(s) for 

another NAAQS of the same pollutant that applies only to its portion of the relevant NAAQS

area, MPOs in each state can determine conformity for the relevant NAAQS independently. 

Where the budget for another NAAQS can be reasonably identified through the interagency 

consultation process, it must be used (40 CFR 93.109(c)(2)(iv)). In addition, any portion of a 

state’s area not covered by those budgets would have to be included in an interim emissions 

test(s), for 

• that part of the relevant NAAQS area not covered by the budget; 

• the state’s entire portion of the relevant NAAQS area; 

OR

• the entire relevant NAAQS area.

The interagency consultation process would be used to determine which test option is selected in 

Scenario 4 areas. Once an area selects a particular interim emissions test and the geographic area 

it will address, the same test must be used consistently for all analysis years. 

4.20 How is the regional emissions analysis done in a multi-state Scenario 4 

area, where only one of the states has its own budget?

The conformity rule requires that if any state has a budget(s), that budget must be used and 

therefore the state would determine conformity independently from the other states in the 

relevant NAAQS area (40 CFR 93.109(c)(2)(iv)). The state or states that have budgets for 

another NAAQS of the same pollutant would use them or portions of them for their regional 

emissions analyses and conformity determinations for the relevant NAAQS area. The state or 

states without those budgets would use the interim emissions test(s) for conformity in the 

relevant NAAQS area and, in the case where two or more states do not have budgets, they would 

determine conformity together. See Section 2 for guidance on determining conformity using the 

interim emissions test(s).
54 

Scenario 4 - General

4.21 What are special issues that the interagency consultation process should 

consider in Scenario 4 areas?

The interagency consultation process is also of key importance in Scenario 4 areas. Where a 

relevant NAAQS area partially covers an area designated for another NAAQS of the same 

pollutant, one or more MPOs may no longer have to determine conformity and one or more new 

MPOs may become part of the interagency consultation process. All MPOs in the relevant

NAAQS area as well as the other parties involved in interagency consultation need to be 

involved in the decision-making process for the area.

Through the interagency consultation process (40 CFR 93.105), the involved parties must decide: 

• whether to apply the interim emissions test(s) to the entire relevant NAAQS area (or in a 

multi-state area, to one state’s portion of the area) or to just the portion not covered by a 

budget for another NAAQS of the same pollutant; 

• whether it is more appropriate for the state DOT or an MPO to prepare the regional 

emissions analysis for a donut area, if there is one; 

• which interim emissions test will be used, in areas that can select only one test; and

• analysis years for the budget test and interim emissions test(s). It may be possible to 

choose analysis years that satisfy both the budget and interim emissions test requirements 

in 40 CFR 93.118(d) and 93.119(g).