Office of Transportation EPA420-B-04-012 

and Air Quality 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 

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 

Transportation and Regional Programs Division

Office of Transportation and Air Quality

U.S. Environmental Protection Agency
page 1 

[signed by Suzanne Rudzinski on July 21, 2004] 

MEMORANDUM: 

From: Suzanne Rudzinski, Director 

Transportation and Regional Programs Division 

Office of Transportation and Air Quality 

To: EPA Regional Air Directors, Regions I - X 

Subject: 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 

Part 1: Introduction 

1. Q. What is the purpose of this guidance? 

A. The Environmental Protection Agency (EPA) published a final transportation 

conformity rule for the new air quality standards on July 1, 2004 (69 FR 40004)1. The 

final rule describes in general terms how conformity will apply to new nonattainment and 

maintenance areas under the 8-hour ozone and PM2.5 standards, and how nonattainment 

areas for the 8-hour ozone standard will use existing adequate or approved motor vehicle 

emissions budgets (“budgets”) in state implementation plans (SIPs) prepared for the 1-

hour ozone standard. The transportation conformity rule (40 CFR part 93) outlines the 

procedures for determining whether federally funded or approved highway and transit 

projects are consistent with (“conform” to) state air quality goals. 

Both EPA and the U.S. Department of Transportation (DOT) agree it is necessary to 

provide additional guidance for conformity implementation to accompany the final rule. 

EPA is issuing this guidance to clarify how conformity determinations and the regional 

1

 This final rule was signed on June 14, 2004, and was available as of that date, before the 

effective date of the 8-hour ozone designations. However, EPA uses the Federal Register 

publication date when referring to a rule, so that readers know in which Federal Register issue to 

find it. 
page 2 

emissions analyses that support them are completed in existing and new nonattainment and 

maintenance areas, particularly those where multiple agencies or states are involved. 

This guidance covers questions such as: 

< What geographic area is covered by the conformity determination and regional 

emissions analysis? 

< How can the regional emissions analysis be implemented? 

< Who does what to develop the regional emissions analysis? 

< What regional emissions test or tests apply for 8-hour ozone nonattainment areas 

with 1-hour ozone SIP budgets? 

This guidance covers both existing nonattainment and maintenance areas as well as areas 

that are designated nonattainment under the new standards, and highlights opportunities 

for flexibility wherever possible. It provides examples and interpretations for generic 

scenarios that are present in the field and that are expected to occur under the new 

standards. It expands on the July 1, 2004, final rule by including additional detail, 

examples, and pictorial representations. However, there may be other cases in the field 

that this guidance does not address. In the event an area’s circumstances are not covered 

in this guidance, EPA, together with DOT, will work with implementers on a case-by-case 

basis. 

This guidance also stresses the importance of the interagency consultation in the 

conformity process. Given the fact that no two areas that implement conformity are 

exactly alike, the interagency consultation process can be used to make the best choices 

for an area’s circumstances, where the rule provides flexibility. The interagency 

consultation provision of the conformity rule, §93.105, requires that general processes be 

established for, and specific decisions be made through, interagency consultation. 

DOT, our federal partner in developing and implementing the conformity rule, assisted in 

the development of this guidance and concurred on its content. 

2. Q. Who can answer questions related to this guidance? 

A. For specific questions about circumstances in particular nonattainment or maintenance 

areas, the EPA Regional Offices, the FHWA Division Offices, and the FTA Regional 

Offices are the first point of contact. A list of EPA Regional conformity staff can be found 

on the web at: http://www.epa.gov/otaq/transp/conform/contacts.htm . 

General questions about this guidance can be directed to Laura Berry, a member of my 

staff at EPA’s Office of Transportation and Air Quality, via her email address: 

berry.laura@epa.gov or phone number: 734-214-4858. 
page 3

3. Q. Does this guidance create new conformity requirements? 

A. No. This guidance is based on conformity implementation precedent to date and the

July 1, 2004, final rule. This document provides guidance to EPA Regional Offices,

FHWA Divisional Offices, FTA Regional Offices, state and local agencies, and the general

public on how EPA intends to exercise its discretion in implementing the statutory and

regulatory provisions for determining conformity in multi-jurisdictional areas. The

guidance is designed to clarify and transmit national policy on these issues. The statutory

provisions and EPA regulations described in this document contain legally binding

requirements. This document does not substitute for those provisions or regulations, nor

is it a regulation itself. Thus, it does not impose legally binding requirements on EPA,

states, or the regulated community, and may not apply to a particular situation based upon

the circumstances. 

This guidance is based on conformity precedent and interpretations made to date. EPA is

issuing this guidance so that the precedents are gathered in one place as a reference for

conformity implementers. EPA retains the discretion to adopt approaches on a case-bycase basis that may differ from this guidance, but still comply with the statute and

conformity regulations. Any decisions regarding a particular conformity determination

will be made based on the statute and regulations. This guidance is a living document and

may be revised periodically without public notice.

4. Q. What do we mean by multi-jurisdictional nonattainment and maintenance areas? 

A. To answer this question, 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/maintenance area is exactly the same as the metropolitan planning

organization (MPO) boundary, as in Figure 1 below. 
page 4

The MPO is the agency that is responsible for preparing metropolitan transportation plans

(“plans”) and transportation improvement programs (TIPs) and demonstrating that plans

and TIPs conform before they are adopted. An MPO is established for each metropolitan

area that has an urbanized population of 50,000 or more according to Section 134 of Title

23, United States Code and Section 5303 of Title 49, United States Code. Section 93.101

of the conformity rule includes the following definition of an MPO: 

“that organization designated as being responsible, together with the state,

for conducting the continuing, cooperative, and comprehensive planning

process under 23 U.S.C. 134 and 49 U.S.C. 5303. It is the forum for

cooperative transportation decision-making.” 

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

from a plan or TIP includes a regional emissions analysis in which emissions from the

planned transportation system are estimated according to §93.122 of the conformity rule. 

In the case where an MPO’s boundaries are the same as the nonattainment (or

maintenance) area’s boundaries, the MPO is responsible for the regional emission analysis

in the entire area. 

However, the boundaries of an MPO do not always correspond to the nonattainment or

maintenance area boundary, nor does a nonattainment or maintenance area always contain

one single MPO. Furthermore, a nonattainment or maintenance area boundary may

encompass portions of more than one state. The conformity rule does not dictate how

MPO planning boundaries are established; MPOs are established according to Titles 23

and 49 of the U.S. Code (as cited above) and DOT’s metropolitan planning regulations. 

Therefore, there may be more than one MPO responsible for transportation planning, and

thus conformity determinations, in a nonattainment or maintenance area, as in Figure 2

below. 
page 5

Or, there may be some portion of the nonattainment or maintenance area that is not

included in an MPO’s jurisdiction, also known as a “donut area” under the conformity

rules. According to §93.101 of the conformity rule:

“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.”

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 in

Figure 3 below.

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

of more than one state, as in Figure 4 below. One MPO may cover the entire multi-state

nonattainment or maintenance area, or MPOs may be established for each state’s portion

of the area. In these situations, states may submit SIPs with identical budgets for the

entire nonattainment or maintenance area, or may submit SIPs with budgets that cover

only their state’s portion of the area.
page 6 

Finally, there are some MPOs in the country which are responsible for transportation 

planning in more than one nonattainment area. This guidance does in general apply to 

such MPOs. The November 24, 1993, conformity rule addresses the case where an MPO 

is responsible for more than one nonattainment 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). 

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

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

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

across the country. 

5. Q. How is this guidance organized? 

A. The remaining parts of this guidance cover how conformity determinations and 

regional emissions analyses that support them are done in nonattainment and maintenance 

areas (“areas”), in the following circumstances: 

• Part 2 covers conformity determinations and regional emissions analyses before an 

area has SIP budgets for conformity. Part 2 applies to all nonattainment areas 

where transportation conformity is required for existing and new air quality 

standards, except 8-hour ozone nonattainment areas with adequate or approved 

SIP budgets for the 1-hour ozone standard (“1-hour budgets”); 

• Part 3 covers conformity determinations and regional emissions analyses after SIP 

budgets are adequate or approved for the applicable pollutant and standard, and 

applies to all existing and newly designated areas where transportation conformity 

is required; and 

• Part 4 covers conformity determinations and regional emissions analyses in 8-hour 

ozone nonattainment areas that have 1-hour budgets, before such areas have 

adequate or approved SIP budgets for the 8-hour ozone standard. 
page 7 

Part 2: Conformity Determinations and Regional Emissions Analyses Before SIP Budgets 

Are Adequate or Approved 

1. Q. To what areas does this part of the guidance apply? 

Part 2 of this guidance applies to areas designated nonattainment for a pollutant identified 

in §93.102(b) of the conformity rule that do not yet have budgets for a standard that can 

be used in conformity. Some examples of areas include: 

• all PM2.5 nonattainment areas before PM2.5 SIP budgets are found adequate or 

approved; 

• 8-hour ozone areas without adequate or approved 1-hour ozone SIP budgets, 

before 8-hour ozone SIP budgets are found adequate or approved; 

• any 1-hour ozone, carbon monoxide, or PM10 nonattainment area that has no 

adequate or approved budgets for that standard. 

This part of the guidance does not cover: 

• 8-hour ozone nonattainment areas without adequate or approved 8-hour budgets, 

but with adequate or approved 1-hour budgets; please refer to Part 4 of this 

guidance. 

• maintenance areas, as these areas by definition have approved SIPs with budgets.2 

2. Q. What tests are used for the regional emissions analysis before a nonattainment area has 

motor vehicle emissions budget(s) that are adequate or approved? 

A. Conformity applies for an air quality standard one year after the effective date of 

EPA’s nonattainment designation for that standard. EPA generally believes that 

conformity will apply for a standard before an area is able to submit a SIP for that 

standard containing budgets and those budgets are found adequate. Section 93.119 of the 

conformity rule provides direction for how the regional emissions analysis must be done 

before budgets are available. During this time period, these areas must use the interim 

emissions test or tests: the build/no-build test, and/or the baseline year test. 

2

A maintenance area could have a special type of maintenance plan called a limited 

maintenance plan. Please see the July 1, 2004, final rule at 69 FR 40063 and the June 30, 2003, 

proposed rule at 68 FR 38983-4 for more information about conformity and limited maintenance 

plans. 
page 8 

3. Q. What geographic area must be examined in regional emissions analyses and conformity 

determinations before a nonattainment area has adequate or approved budgets? 

A. In this case, a conformity determination for a transportation plan, TIP, or project not 

from a plan or TIP must be based on a regional emissions analysis that covers the entire 

nonattainment area, to satisfy the statute and regulations. Section 93.122(a)(1) of the 

conformity rule states: 

“the regional emissions analysis required by §§93.118 and 93.119 for the 

transportation plan, TIP, or project not from a conforming plan and TIP 

must include all regionally significant projects expected in the 

nonattainment or maintenance area.” 

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. Please see the next Q & A 

for the options in creating a regional emissions analysis for an entire area. 

For all nonattainment areas covered by Part 2 of the guidance, the MPO(s) must 

coordinate their plan/TIP conformity determinations together, pursuant to §93.124(d) of 

the final conformity rule. In the November 24, 1993, final rule, EPA stated: 

“Where a nonattainment area includes multiple MPOs, the control strategy 

SIP may either allocate emissions budgets to each metropolitan planning 

area, or the MPOs must act together to make a conformity determination 

for the nonattainment area.” 

Once DOT receives all plan/TIP conformity determinations for a given nonattainment 

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

MPO to update or revise its plan and TIP, a DOT conformity determination for each plan 

and TIP in that nonattainment area must be made at the same time, according to 

§93.124(d) of the rule. 

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

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

that the requirements of Clean Air Act section 176(c)(1) are met. That is, before SIP 

budgets are 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 or any other milestone in the nonattainment area, it is necessary to consider 

emissions from the entire area in one regional emissions analysis, and for DOT to make all 

plan/TIP conformity determinations at the same time. 
page 9 

4. Q. How can multiple jurisdictions create a regional emissions analysis for the entire 

nonattainment area? 

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

more than one MPO or a donut area must use the consultation process required by 

§93.105 of the conformity rule to decide how best to meet this requirement, regardless of 

whether the area is within one state or is a multi-state area. The 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 the next Q&A. 

Nonattainment Areas With More Than One MPO, In One or More States: 

In nonattainment areas where there is more than one MPO, the MPOs can develop the 

regional emissions analysis for the area in either one of two ways: 

1. by separate modeling by each MPO that is combined into one regional analysis; or 

2. by one modeling analysis for the entire nonattainment area. 

If MPOs in the nonattainment area want to model their emissions separately, each MPO 

would do a regional emissions analysis that includes the existing transportation system in 

its part of the nonattainment area as well as all new projects in its plan and TIP. Each 

MPO 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 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 compiled for the entire nonattainment area to satisfy conformity 

requirements for an MPO’s 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). 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 plans 

and TIPs. Again, these modeling results would be presented in one regional emissions 

analysis for the entire nonattainment area that would accompany the conformity 

determinations for new or revised plans/TIPs in the nonattainment area. 

As an 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, 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. 
page 10 

Alternatively, the MPOs could initially create one regional emissions analysis for the entire 

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

In either case, to make the demonstration required by the conformity rule, all MPOs must 

use the same test and the same analysis years for the regional emissions analysis. MPOs in 

one nonattainment area may want to coordinate their plan and TIP update cycles as well 

as the length of their plans, as described in the following bullets. 

< New or revised plans and TIPs, as well as significant changes to projects, could 

require a new regional emissions analysis (see §§93.104 and 93.122(g) of the 

conformity rule). Coordination of plan and TIP update 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. 

< Different transportation plan lengths within one nonattainment area would require 

additional analysis years, because according to §93.119(g), an analysis must be 

performed for the last year of each plan. For example, if one MPO’s plan ends in 

2025 and another MPO’s plan ends in 2030, both years would have to be analyzed 

in the regional analysis for the entire nonattainment area. Coordination of plan 

lengths may minimize the number of analysis years that have to be examined in any 

one regional emissions analysis. 

Nonattainment Areas With a Donut Area:

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

the conformity rule requires the MPO to include the emissions estimated from the donut

area’s existing and proposed transportation system in the regional emissions analysis for

metropolitan transportation plan and TIP conformity determinations. However, either the

MPO or the state transportation agency (“state DOT”) could estimate emissions from the

donut area as decided through interagency consultation, as explained in Q&A 7 of this

part.

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

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

interim emissions test or tests, according to the requirements of §93.119. Again, the 

consultation process would be used to coordinate the choice of tests and analysis years 

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

analysis years must be used as noted above. 
page 11 

5. Q. What decisions must be made in the interagency consultation process? 

A. 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 

donut area in a nonattainment area, should use the interagency consultation process to 

make certain decisions. Under the conformity rule, there are some 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 above. These 

include: 

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

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

same time; 

• how the regional emissions analysis is developed, i.e., whether emissions will be 

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

for the nonattainment area as a whole; 

• the interim emissions test the nonattainment area will meet, in the areas that must 

meet only one test as required by §93.119 (e.g., PM2.5 areas or 8-hour ozone areas 

that are classified as marginal or designated under Clean Air Act, part D, subpart 1 

that do not have 1-hour budgets). 

EPA believes that for consistency and in order to satisfy 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. 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 the rule requires that one 

test be met for the entire nonattainment area, according to §§93.119 and 

93.124(d);3 

• the analysis years for the interim emissions test(s), as required by §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 

3

In 8-hour and 1-hour 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 §93.119. Please read Section IV.D. of the preamble of the July 1, 2004, final rule 

for further explanation. 
page 12 

the same time period and thus need to include the last year of each transportation 

plan. 

As described in the above example, in a nonattainment area with two MPOs where 

one MPO’s transportation plan covers a 25-year period from 2005 to 2030, and 

the other MPO’s plan covers only a 20-year period from 2005 to 2025, the 

regional emissions analysis for both MPOs must examine emissions in the years 

2025 and 2030; and 

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

is more than one emissions model version that could be used, per §93.111 of the 

rule. 

In addition, the MPO jurisdictions 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. Section 93.105(c)(1)(i) of the rule 

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. 

6. Q. In a nonattainment area that does not have SIP budgets for conformity, if one MPO in 

the area can meet the requirements of §93.119 of the rule, but another MPO or a donut 

area cannot, can the MPO that meets the requirements show that its plan and TIP conform 

and proceed? 

A. No. EPA believes that before budgets are adequate or approved, the whole 

nonattainment area must conform to meet the Clean Air Act 176(c)(1) requirements. 

These requirements are that transportation activities will not: 

< cause a new air quality violation, 

< increase the frequency or severity of a violation, or 

< delay timely attainment or any other milestone in the area for an air quality 

standard. 

It is necessary to estimate emissions from the entire nonattainment area in all plan/TIP 

conformity determinations and the supporting regional analysis because separate SIP 

budgets are not yet available. For example, in Figure 2 repeated below, there are two 

MPOs. If they choose to model their emissions separately and West MPO appears to pass 

the applicable test(s) of §93.119 but East MPO does not, West MPO cannot proceed to 

determine conformity alone. It cannot be known for sure that West MPO’s transportation 

plan and TIP would not cause a new violation, increase the frequency or severity of a 
page 13

violation, or delay timely attainment (or other milestone) in the area, because East MPO

cannot also pass the test. Thus, the nonattainment area in this example as a whole cannot

demonstrate that it will not cause or contribute to violations. To resolve this situation,

East and West MPOs would consult on what options are available for demonstrating

conformity, including the option of adding or modeling their emissions together to see if

they pass the applicable regional emissions test(s). 

7. Q. Who is responsible for estimating emissions in a donut area of a nonattainment or

maintenance area?

A. 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:

• he MPO within the nonattainment area. In some cases, an adjacent MPO is better

suited to conduct such an analysis. An MPO could run an analysis for the donut

area’s projects, or include the donut area’s projects in the regional emissions

analysis supporting its plan and TIP. An MPO could also include the donut area’s

projects in its plan and TIP, but this practice is not common;

• the state DOT. In some cases, the state DOT may take the lead in conducting

regional emissions analysis for the donut area; 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. 

Section 93.105(c)(3) of the conformity rule 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 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 §51.390 of the

rule.

t
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page 15 

Part 3: Conformity Determinations and Regional Emissions Analysis Once SIP Budgets 

Are Adequate/Approved 

General 

1. Q. To what areas does this part of the guidance apply? 

A. Part 3 applies to areas designated nonattainment for any pollutant identified in 

§93.102(b) of the rule, once the area has adequate or approved budgets from a SIP 

addressing a particular standard for a pollutant. This part of the guidance applies to: 

• an 8-hour ozone nonattainment area once it has adequate or approved budgets for 

the 8-hour standard, regardless of whether or not the area had 1-hour budgets; 

• a PM2.5 nonattainment area once it has adequate or approved PM2.5 SIP budgets; 

• any 1-hour ozone, carbon monoxide, or PM10 nonattainment area that has 

adequate or approved budgets from a SIP addressing that standard; and 

• maintenance areas, as these areas by definition have approved SIPs with budgets.4 

2. Q. How do nonattainment and maintenance areas determine conformity for a given 

standard once adequate or approved SIP budgets are available for that standard? 

A. Clean Air Act section 176(c)(1) states that federal activities must conform to the SIP. 

Once a SIP with budgets has been submitted and EPA finds the budgets adequate or 

approves the SIP, the “budget test” using the new budgets must be used for conformity 

determinations according to §§93.109 and 93.118 of the conformity rule. 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, 

attainment, or maintenance of an air quality standard; and 

4

A maintenance area could have a special type of maintenance plan called a limited 

maintenance plan. Please see the July 1, 2004, final rule at 69 FR 40063 and the June 30, 2003, 

proposed rule at 68 FR 38983-4 for more information about conformity and limited maintenance 

plans. 
page 16 

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

the control measures in the SIP.5 

3. Q. What geographic areas might budgets from a SIP address, and how is 

conformity generally determined in multi-jurisdictional areas with SIP budgets? 

A. In a nonattainment or maintenance area located entirely within one state, the state air 

agency may develop a SIP that establishes either: 

• a budget (or budgets) that applies to the entire nonattainment or maintenance area, 

or 

• a subarea budget (or budgets) for each MPO within the nonattainment or 

maintenance area. 

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

establish SIPs in each state that contain either: 

• identical budgets that apply to the entire nonattainment or maintenance area, or 

• unique budgets that apply only to one state’s portion of the nonattainment or 

maintenance area. 

State and local agencies can develop SIPs in many different ways. Section 93.124(d) of 

the conformity rule acknowledges this fact and covers SIPs developed in areas where 

there is more than one MPO: 

“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 approved, the conformity determination(s) and 

regional emissions analysis is 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 in how the regional emissions analysis is developed, and in coordinating 

conformity determinations, when several MPOs are involved. The table on the next page 

summarizes the general situations. The questions and answers that follow provide further 

detail on the different circumstances that can occur. 

5

 There are other criteria that SIP budgets must meet for EPA to find them adequate; for 

the full list of adequacy criteria, see §93.118(e) of the conformity rule. 
page 17 

Summary Table: How SIPs Affect Geographic Areas Considered in Conformity 

For a nonattainment 

or maintenance area 

located: 

where SIP budgets 

are established for: 

the geographic area 

considered in 

regional analysis 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 done when there is more 

than one MPO. See below for more details. 

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

maintenance area because there may be more than one MPO making determinations for 

separate plans and TIPs. There is flexibility in how these conformity determinations are 

coordinated. See below for more details. 

Nonattainment or Maintenance Areas Located in One State, Where Budgets Are Established for 

the Entire Area 

4. Q. How is conformity done when budgets are established for an entire nonattainment or 

maintenance area that is within one state? 

One MPO. In the simplest case, an area is located entirely within one state and the MPO 

boundary is the same as the nonattainment/maintenance area boundary (Figure 1). In 

Figure 1, the nonattainment or maintenance area boundary, the MPO, and the SIP budgets 

all address the same geographic area. In this case, because the SIP establishes budgets for 

the entire area, the MPO will use those budgets in the regional emissions analysis done for 

the MPO’s plan/TIP conformity determination for the entire nonattainment or maintenance 

area. 
page 18

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 plan/TIP conformity determinations and submit them to DOT, as

explained in Part 2, Q & A 3. Once all 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

§93.118 of the rule that would accompany all 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 plan and TIP using the regional

emissions analysis done for the entire area. See Part 2, Q & A 4 for more information.

The MPOs can develop the regional 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. EPA believes that the MPOs must all use the same analysis years when

completing the budget test in accordance with §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, §93.118 of the

conformity rule would be met if estimated emissions in each analysis year are less

than or equal to the area’s applicable budgets. 

MPOs in one nonattainment or maintenance area may want to coordinate their plan and

TIP update cycles as well as the length of their plans. 

< New or revised plans and TIPs, as well as significant changes to projects, could

require a new regional emissions analysis (see §§93.104 and 93.122(g) of the

conformity rule). Coordination of plan and TIP update 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. 
page 19 

< Different transportation plan lengths within one nonattainment or maintenance area 

would require additional analysis years, because according to §93.118(d), an 

analysis must be performed for the last year of each plan. For example, if one 

MPO’s plan ends in 2025 and another MPO’s plan ends in 2030, both years would 

have to be analyzed in the regional analysis for the entire nonattainment area. 

Coordination of plan lengths may minimize the number of analysis years that have 

to be examined in any one regional emissions analysis. 

One or More MPOs and a Donut Area: If there is only one MPO in the nonattainment 

or maintenance area conducting conformity determinations, the regulations require the 

MPO to include the emissions estimated from the donut area’s existing and proposed 

transportation system in the regional emissions analysis for the metropolitan transportation 

plan and TIP conformity determinations. However, either the MPO or the state 

transportation agency (“state DOT”) could estimate emissions from the donut area as 

decided through interagency consultation, as explained in Part 2, Q&A 7. 

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 plan/TIP conformity determinations. The emissions estimated from the 

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

according to the requirements of §93.118. The consultation process would be used to 

coordinate the analysis years when several agencies are completing emissions analyses, 

because the same analysis years must be used. 

Nonattainment or Maintenance Areas Within One State, Where the SIP Establishes Subarea 

Budgets 

5. Q. How do nonattainment or maintenance areas with more than one MPO in a single state 

determine conformity once SIP budgets are adequate or approved, and the SIP establishes 

subarea budgets for each MPO? 

A. 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 transportation sector and 

still make progress toward, attain, or maintain the standard. Therefore, if each MPO 

meets its subarea budgets for a pollutant and standard in accordance with the requirements 

of §93.118, then the entire area meets the total SIP’s purpose for that pollutant and 

standard. As EPA noted in the January 11, 1993, conformity proposal, 
page 20 

“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). 

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

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

§93.124(c) and (d) of the conformity rule. Section 93.124(c) states: 

“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 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 

plan/TIP determination. In other words, under the conformity rule in order for an MPO or 

DOT to determine conformity for its subarea, the rest of the area must also be in 

conformity. The preamble to the November 24, 1993, conformity 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, it must be demonstrated that all 

subareas have conforming plans and TIPs. For example, suppose the subarea budgets in a 

SIP have just been found adequate, and one of the MPOs in the area needs to update its 

TIP. That MPO can make a conformity determination using its subarea budgets for the 

first time without waiting for the other MPOs in the area, as long as the other MPOs have 

conforming plans and TIPs in place, even if these plans and TIPs were previously found to 

conform using the interim emissions test(s). 
page 21 

Once an area has adequate or approved subarea budgets, if conformity lapses6

 for one 

subarea, the other subarea(s) can continue to implement projects in their currently 

conforming plans and TIPs, but they cannot make new plan and TIP conformity 

determinations until the lapse is resolved and conformity is determined in the lapsed 

subarea. In other words, if the conformity status of one subarea lapses, the existing plans 

and TIPs in other subareas continue to be valid and consequences would not apply to any 

other subareas unless the lapse is not resolved by the time other subareas need to make 

new conformity determinations. 

6. Q. Why can’t an MPO that has its own subarea budgets determine conformity of its 

transportation plan and TIP when another MPO in the same area is in a lapse? 

A. Section 176(c) of the Clean Air Act 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 lapses, it has not demonstrated that it can conform to its subarea 

budgets. 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 as a whole. Using 

Figure 2 again as an example (found in Part 2, Q & A 6), if East MPO is in a conformity 

lapse, it cannot be assured that West MPO’s transportation activities still 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 SIP’s purpose of progress toward, attainment of, or maintenance of the standard, 

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. 

6

A lapse is defined in §93.101 of the rule: “Lapse means that the conformity determination 

for a transportation plan or TIP has expired, and thus there is no currently conforming 

transportation plan or TIP.” A lapse occurs when conformity of a plan or TIP is not determined 

according to the frequency requirements of §93.104 of the conformity rule. 
page 22 

7. Q. How do I know whether the SIP establishes subarea budgets? Are county-by-county 

emissions projections subarea budgets? 

A. 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. Section 93.124(c) of the conformity rule states, 

“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.” 

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 plan/TIP conformity determinations 

for the entire nonattainment or maintenance area approved by DOT at the same time, as 

described above in Q & A 4 of this part and Part 2, Q & A 4. According to §93.124(d), 

“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.” 

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

budgets, they should communicate their preference to the state and local air agencies 

within the interagency consultation process during the development of the SIP. Section 

93.105(c) of the conformity rule requires interagency consultation on the development of 

SIPs, as well as transportation plans, TIPs, and conformity determinations. 

Multi-State Nonattainment/Maintenance Areas: 

8. Q. 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? 

A. If these multi-state areas have SIPs that contain 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 §93.118 of the conformity rule. This 

regional analysis would accompany all plan/TIP conformity determinations in the area that 

would be submitted to DOT. Once all determinations for a given area are received, DOT 

would make its conformity determinations at the same time. The MPOs must collectively 
page 23

develop a regional emissions analysis for the entire area that meets the requirements of

§93.118 that would accompany all 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 plan and TIP using the regional emissions analysis

done for the entire area. 

For example, in Figure 4, repeated 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 oval and the conformity determinations for each MPO’s plans and

TIPs within the area would be based on this regional emissions analysis. DOT would wait

to make its conformity determinations for the plans and TIPs in the area until it receives all

of them. This answer is similar to single state areas with SIP budgets that cover the entire

nonattainment or maintenance area. See Q & A 4 of the part, and Part 2, Q & A 4, for

further information.

9. Q. When would it be likely for state air agencies in a multi-state nonattainment or

maintenace area to submit SIPs with budgets that apply to the entire area? 

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

for the 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

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

would need to cover the entire nonattainment or maintenance area pursuant to

§§93.124(d) and 93.118. 
page 24 

10. Q. How is conformity determined for multi-state nonattainment or maintenance areas 

when each state submits a SIP that contains budgets only for its state’s portion of the 

area? 

A. 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 Clean Air Act 

requirement. Where states have done so and EPA has found such budgets adequate, the 

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

independently of the other states. EPA concluded that these states can operate 

independently for conformity because the Clean Air Act refers to conformity to a SIP. 

Each state’s SIP in these cases includes inventories, control measures and programs, and 

budgets that apply to only that state’s portion of the nonattainment or maintenance area. 

States that have SIPs with adequate or approved budgets for only their own portions of a 

multi-state area are distinct from MPOs in a nonattainment or maintenance area that have 

subarea budgets within the same SIP, and also distinct from states that have SIP budgets 

that apply to an entire multi-state nonattainment or maintenance area. Where states have 

their own SIP budgets, if a conformity lapse is occurring in one state’s portion of an area, 

the MPO(s) in the other state(s) in the nonattainment or maintenance area can continue to 

make conformity determinations for new or revised transportation plans and TIPs because 

they continue to show conformity to their SIP’s budgets. 

Using Figure 4 above as an example, suppose States A, B, and C each have SIPs with 

adequate or approved budgets that apply only to their own state’s portion of the area. If 

State A lapses, States B and C can continue to make new conformity determinations. In 

contrast, as described previously: 

• MPOs that have subarea budgets within one SIP are determining conformity to the 

same SIP, therefore when one makes a conformity determination, all other 

subareas must be in conformity as well in order to show conformity to the SIP; and 

• multi-state areas that have budgets for the entire nonattainment or maintenance 

area are also determining conformity to the same SIP, therefore, there must be one 

regional emissions analysis for this area and conformity determinations for plans 

and TIPs in the area must be made at the same time as described in Q & A 8 of this 

part. 
page 25 

Part 4: Conformity Determinations and Regional Emissions Analyses in 8-Hour Ozone 

Nonattainment Areas With Adequate or Approved 1-Hour SIP Budgets 

Background 

1. Q. To what areas does this part of the guidance apply? 

A. This part of the guidance clarifies the implementation of conformity in nonattainment 

areas for the 8-hour ozone standard that were nonattainment or maintenance areas for the 

1-hour ozone standard and have adequate or approved SIP budgets that address the 1-

hour ozone standard. However, this part of the guidance applies only until these areas 

have 8-hour budgets that they can use for conformity. Once an area submits an 8-hour 

SIP with budgets and EPA finds the budgets adequate or approves the 8-hour SIP that 

contains budgets, that area must use the 8-hour budgets for conformity according to 

§93.109(e)(1) of the conformity rule. At that point, Part 3 of this guidance would apply, 

and Part 4 would no longer be relevant to that area. In Part 4 of the guidance, the terms: 

• 8-hour area means a nonattainment area for the 8-hour ozone standard, and 

• 1-hour area means a nonattainment or maintenance area for the 1-hour standard. 

The July 2004 final rule allows 8-hour areas with 1-hour SIPs to implement conformity in 

the same way as they have been under the 1-hour standard, to the extent possible. In 

other words, the 8-hour areas with 1-hour budgets will continue to use them wherever 

possible. This part of the guidance is intended to assist in understanding how that general 

principle applies in various circumstances. 

2. Q. How is Part 4 organized? 

A. Part 4 is organized under headings for background, boundary scenario, and general 

implementation topics, as follows: 

Background (questions 1 - 8); 

Scenario 1 (questions 9 - 11); 

Scenario 2 (questions 12 - 13); 

Scenario 3 (questions 14 - 18); 

Scenario 4 (questions 19 - 22); and 

General Implementation of the Final Rule (questions 23 - 25). 
page 26

3. Q. What are the ways an 8-hour area could be related to a 1-hour area that has adequate

or approved 1-hour budgets?

A. As described in the July 1, 2004, conformity rule, there are four generic scenarios for

how 8-hour area boundaries relate to 1-hour area boundaries, and the conformity rule is

written with these four scenarios in mind. 

To determine which scenario appropriately describes an area, it is necessary to consider

the boundary of the entire 8-hour area. For example, in a multi-state 8-hour area, the 8-

hour boundary refers to the entire multi-state area, rather than each state’s individual

portion. Figure 5 illustrates the four generic boundary scenarios. 

• Scenario 1: the 8-hour area boundary and the 1-hour area boundary are identical.

• Scenario 2: he 8-hour area boundary is smaller than the 1-hour area boundary.

• Scenario 3: the 8-hour area boundary is larger than the 1-hour area boundary. 

• Scenario 4: he 8-hour area boundary partially overlaps the 1-hour area boundary. 

4. Q. Do 8-hour areas with 1-hour budgets have to use the 1-hour budgets for conformity

determinations under the 8-hour standard?

A. Yes, in most cases. As required in §93.109(e)(2) of the July 2004 final rule, the 1-

hour budgets must be used for 8-hour conformity determinations, unless the interim

emissions test(s) is more appropriate as decided through the interagency consultation

process (see §93.109(e)(2)(v)). Section 176(c) of the Clean Air Act states that

transportation activities must not cause new violations, increase the frequency or severity

t

t
page 27 

of existing violations, or delay timely attainment. Using 1-hour budgets where available 

and appropriate ensures that air quality progress to date is maintained, air quality will not 

be worsened and attainment of the 8-hour standard will not be delayed because of 

emissions increases prior to the development of SIPs with 8-hour budgets. Once EPA 

finds a budget adequate or approves the SIP that includes it, the budget test provides the 

best means to determine whether transportation plans and TIPs meet Clean Air Act 

conformity requirements. EPA believes this principle applies with respect to the 1-hour 

budgets in 8-hour nonattainment areas as well: in most cases, the 1-hour budgets are the 

best test for determining conformity to the 8-hour standard before 8-hour budgets are 

available because the 1-hour budgets have led to current air quality improvements. 

5. Q. Are there circumstances under which an 8-hour area with 1-hour budgets would not 

use them? 

As described in the preamble to the July 2004 final rule (69 FR 40025), though EPA 

anticipates that exceptions to the use of the 1-hour budgets will be infrequent, there are 

some cases where using the interim emissions test(s) may be more appropriate to meet 

Clean Air Act requirements. EPA expects such limited cases to be supported and 

documented in the 8-hour conformity determination for a given area. EPA notes that an 

adequate or approved 1-hour SIP budget cannot be considered inappropriate simply 

because it is difficult to pass for 8-hour conformity purposes. In addition, as noted below 

and consistent with past conformity precedent, 1-hour budgets cannot be discarded simply 

because they are based on older planning assumptions or emissions models, unless through 

interagency consultation it is determined that a different emissions test(s) is more 

appropriate to ensure that air quality is not worsened for all 8-hour areas and that 

reductions are achieved in certain ozone areas. 

The most likely example of when the 1-hour budgets may not be the most appropriate test 

is where a 1-hour budget is not currently used in conformity determinations for the 1-hour 

standard, and thus is currently not relied upon to measure whether transportation activities 

are consistent with Clean Air Act requirements. Such a case would happen when the 1-

hour budget year is no longer in the timeframe of the transportation plan and there is no 

requirement to meet the budget test prior to the year in which the next 1-hour budget is 

established, (e.g., the SIP established a budget for the 1-hour attainment year, but that 

attainment year has passed and budgets for future years are available). For example, 

suppose a 1-hour maintenance area attained in 1999 and has a maintenance plan with 

budgets for 2009. If the area has an 8-hour attainment date of 2007, for an 8-hour 

conformity determination it would have to compare emissions in 2007 to the budgets from 

the most recent prior year, which would be the 1-hour attainment budgets for the year 

1999. In this case, the budgets are not currently in use for the 1-hour standard, and it may 

be more appropriate for an area to use the 2002 baseline year test for the 2007 analysis 

year in the 8-hour conformity determination, since the 2002 baseline could be lower and 
page 28 

therefore more protective than the 1999 budgets. However, the maintenance area would 

use its 2009 budgets in the 1-hour maintenance plan to show 8-hour conformity for 2009 

and all future analysis years. 

However, if the budget year has passed but the budgets have continued to be used for 

conformity for the 1-hour standard, they would likely continue to apply for 8-hour 

conformity. For example, suppose a severe 1-hour nonattainment area has budgets only 

for its 2005 attainment year. Once the 8-hour standard applies and before the area has 

adequate or approved 8-hour budgets, the area would likely continue to use its 1-hour 

attainment budgets for all analysis years for 8-hour conformity determinations, even after 

the year 2005 is no longer in the timeframe of the transportation plan. Note, although the 

2005 budgets would be used after 2005 is no longer in the timeframe of the plan, 2005 

would no longer be a required analysis year. 

Another example of when the interim emissions test(s) would be more appropriate than 

existing adequate or approved 1-hour budgets would be in certain Scenario 4 areas where 

it is impossible to determine which portion of a 1-hour budget covers an 8-hour 

nonattainment area. In this case, applying the budget test with 1-hour budgets is not 

feasible, and consequently, only the interim emissions test(s) are available for such unique 

areas. 

As described in Section V. of the July 1, 2004, preamble (69 FR 40019 - 21), when a SIP 

budget is not established a moderate or above ozone area would need to pass both interim 

emissions tests. Areas classified as marginal or designated under Clean Air Act, Part D, 

subpart 1 can choose between the two tests when no budgets apply. However, in these 

cases where a 1-hour budget is available but the area demonstrates it is not the most 

appropriate test, EPA believes that the no-greater-than-2002 baseline year test would 

most likely be used. EPA believes it is extremely unlikely that the build/no-build test alone 

would ever be a more appropriate test than the budget test with existing 1-hour budgets 

that are currently used for conformity purposes. Please refer to the July 1, 2004, rule 

preamble on this point (69 FR 40025). 

Areas must use the consultation process to decide whether the applicable interim 

emissions tests are more appropriate to meet Clean Air Act requirements than the budgets 

in each 1-hour SIP. As described in the first example above, there may be cases where an 

area has multiple 1-hour SIPs, some of which have appropriate budgets while others do 

not. In areas where only one interim emissions test may be selected, the rule requires that 

areas must also justify selection of the specific test chosen as being more appropriate for 

meeting Clean Air Act requirements than the available 1-hour budgets. This decision 

should be discussed with all interagency consultation parties and documented in the 

conformity determination for the 8-hour standard. (Please refer to the preamble of the 

July 2004 final conformity rule at 69 FR 40025 for more information.) 
page 29 

6. Q. In 8-hour areas with 1-hour subarea budgets, do all subareas have to use the 1-hour 

budgets for 8-hour conformity determinations? Likewise, in multi-state 8-hour areas 

where each state has separate 1-hour budgets, do all states have to use their 1-hour 

budgets for 8-hour conformity? 

A. In general, each subarea or state can determine conformity independently as long as 

everyone is using 1-hour budgets to determine conformity. However, in the unlikely 

event that one subarea or state determines that its 1-hour budgets are inappropriate, other 

subareas or state budgets may also be inappropriate. See Part 3 of this guidance for 

further rationale for conformity determinations using subarea and multi-state SIP budgets. 

When any subarea or state believes that is inappropriate to use its budgets, all subareas or 

states would consult to determine the impact on future conformity determinations. EPA 

believes that where one subarea or state determines its budgets are inappropriate, it is 

likely that the other budgets are also inappropriate because they are collectively intended 

to address the same Clean Air Act purpose. 

EPA notes, however, that in a Scenario 4 area, the circumstances are different and more 

complex. In these areas, the 8-hour area partially overlaps the 1-hour area. In a multiple 

MPO or multi-state Scenario 4 area, it may be the case that one or more other MPOs or 

states cannot use their 1-hour budgets because it is not possible to determine what portion 

of the budgets apply. However, other MPOs or states may still be able to use their 1-

hour budgets for their portions of the 8-hour area. See below for further information on 

the various scenarios. 

7. Q. In an 8-hour area with a 1-hour SIP that establishes subarea budgets, how should 

MPOs demonstrate conformity for the first time under the 8-hour standard? 

A. As described in Part 3 of this guidance, when an area has subarea budgets, conformity 

for an MPO’s plan and TIP can only be determined if all other subareas have conforming 

transportation plans and TIPs in place for a given pollutant and standard. 

To the extent possible, EPA believes that the subarea budgets must be used in the 8-hour 

conformity determination, unless it is determined through consultation that they are not 

appropriate for meeting Clean Air Act conformity requirements. Subarea budgets in 1-

hour SIPs must continue to be used under the conformity rule for the 8-hour standard, 

because they ensure that air quality progress to date is maintained. 

In general, where an 8-hour area has multiple MPOs with subarea budgets for the 1-hour 

standard, EPA and DOT believe it is necessary for the first conformity determination 

under the 8-hour standard to be done as follows: each MPO would show its plan and TIP 

conform to its 1-hour subarea budgets independently. All of the MPOs’ plan/TIP 

conformity determinations would then be submitted to DOT for its determinations. DOT 
page 30 

will not make its conformity determination on any of the plans or TIPs from the 8-hour 

area until every MPO in the area has made a conformity determination for its plan and 

TIP. Please note that this answer may differ for Scenario 3 and 4 areas where an 

additional portion of the 8-hour area is not covered by the 1-hour budgets (these 

Scenarios are discussed later in this part, beginning with Q & 14). All MPOs in the 8-hour 

area must have an initial valid conformity determination for the 8-hour standard by the end 

of the one-year grace period. If any do not, DOT will be unable to make any 8-hour 

conformity determinations for the 8-hour area, and all of the MPOs’ plans and TIPs will 

lapse. 

8. Q. How are subsequent 8-hour conformity determinations made in an 8-hour area where 

the 1-hour SIP establishes subarea budgets? 

A. In general, once DOT has made its initial 8-hour conformity determination for the area, 

the MPOs will operate as usual: before any MPO in the area determines conformity using 

subarea budgets, all other MPOs in the area must have a conforming plan and TIP in 

place. If one subarea is in a conformity lapse, conformity determinations for new or 

revised plans and TIPs cannot be made in other subareas until the lapse ends. This answer 

may differ for Scenario 3 and 4 areas where an additional portion of the 8-hour area is not 

covered by the 1-hour budgets (discussed later in this part, beginning with Q & A 14). 

Scenario 1 Areas 

9. Q. How is conformity demonstrated in Scenario 1 areas when the 1-hour SIP budgets 

apply to the entire 1-hour area? 

A. Using 1-hour budgets for 8-hour conformity determinations is straightforward in 

Scenario 1 areas, because the boundaries of the 8-hour area and 1-hour area(s) are exactly 

the same. The MPO or MPOs must coordinate their plan/TIP conformity determinations 

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

the 8-hour area, DOT will make its conformity determinations at the same time. If there is 

more than one MPO, the planning agencies will have to work together to develop one 

regional emissions analysis for the entire 8-hour area under §93.109(e)(2)(i), just as they 

would have been doing for the 1-hour standard. Please see Part 3 of this guidance for 

further information regarding how a regional emissions analysis could be completed for 

these areas. 

Note that a Scenario 1 8-hour area could be formed from one or more 1-hour areas with 

adequate or approved 1-hour budgets for the entire 8-hour area. 
page 31 

10. Q. How is conformity demonstrated in Scenario 1 areas when the 1-hour SIP includes 

subarea budgets? 

A. As discussed in Part 3, Q & A 1, conformity follows the SIP. Therefore, conformity 

and the supporting regional emissions analysis is done for the geographic area that is 

covered by the SIP’s budgets, i.e., each subarea’s portion of the nonattainment area. See 

Part 3, Qs & As 5 - 7, and Qs & As 7 and 8 of this part for additional information. 

11. Q. How is conformity demonstrated in multi-state Scenario 1 areas, where each state has 

its own separate 1-hour SIP budgets? 

A. As discussed in Part 3, Q & A 1, conformity follows the SIP. Therefore, conformity 

and the supporting regional emissions analysis is done for the geographic area that is 

covered by the SIP’s budgets, i.e., each state’s portion of the nonattainment area. 

Before 8-hour ozone budgets are found adequate or approved, EPA concludes that where 

each state has its own 1-hour budgets, each state can continue to demonstrate conformity 

to its SIP independently for the 8-hour ozone standard. Therefore, conformity 

determinations for the 8-hour standard can be made in one state of a multi-state 8-hour 

area even if a lapse is occurring in another state in the 8-hour area, or conformity had not 

yet been determined for the 8-hour ozone standard in another state in the area. This 

independence in a multi-state 8-hour area applies as long as all states are using 1-hour 

budgets to determine conformity. Please see Part 3 of this guidance for further 

information regarding how a regional emissions analysis could be completed for these 

areas. 

Scenario 2 

12. Q. How is conformity demonstrated in Scenario 2 areas, when the 1-hour SIP establishes 

budgets that apply to the entire 1-hour area? 

A. Regardless of whether the area is located entirely within one state, or is a multi-state 

area, the MPO or MPOs must coordinate plan/TIP conformity determinations and submit 

them to DOT to satisfy the conformity rules. Once DOT receives all plan/TIP conformity 

determinations for the 8-hour or 1-hour area (as applicable), DOT will make its 

conformity determinations at the same time. Please see Part 3 of this guidance for further 

information regarding how a regional emissions analysis could be completed for these 

areas. 

[answer continues next page] 
page 32

These areas can choose either of two versions of the budget test, as required by

§93.109(e)(2)(ii): 

• the budget test using the subset or portion of existing adequate or approved 1-hour

budgets that cover the 8-hour area, where such portion can be appropriately

identified (§93.109(e)(2)(ii)(A)); or

• the budget test using the existing adequate or approved 1-hour budgets for the

entire 1-hour area, however in this case any additional emissions reductions needed

to pass the budget test must come from within the 8-hour area

(§93.109(e)(2)(ii)(B)).

The interagency consultation process should be used to determine whether budgets for the

8-hour area can reasonably be derived from the 1-hour budgets. It may be possible to

create budgets for only the 8-hour area, for example if the 1-hour SIP contains estimates

of emissions by county in the years for which budgets are established, and emissions from

the county or counties not included in the 8-hour area can be subtracted from the 1-hour

budgets. 

In Figure 6 below:

Budget for 8-hour area 1-hour budget – county or counties not in the 

8-hour area

(Area in the bold line) = (emissions in the – (emissions from 

 gray circle) the crescent shape)

If is not possible to create budgets that apply to only the 8-hour area, the MPO or MPOs

will have to determine conformity to the 1-hour budgets for 8-hour conformity as they

have for the 1-hour standard, and if reductions are needed to meet the budgets, they must

come from within the 8-hour area (inside the bold line in Figure 6) as required by the

conformity rule.

= 
page 33

Note that a Scenario 2 8-hour area could be formed from one 1-hour area as in Figure 6

above, or more than one 1-hour area with adequate or approved 1-hour budgets for the 8-

hour area, as depicted in Figure 7, below. In these cases, consultation should be used to

determine how the 1-hour budgets will apply.

13. Q. How is conformity demonstrated in multi-state Scenario 2 areas, where each state has

its own separate 1-hour SIP budgets?

A. As discussed in Part 3, Q & A 1, conformity follows the SIP. Therefore, 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. 

Before 8-hour ozone budgets are found adequate or approved, EPA concludes that where

each state has its own 1-hour budgets, each state can continue to demonstrate conformity

to its SIP independently for the 8-hour ozone standard. Therefore, conformity

determinations for the 8-hour standard can be made in one state of a multi-state 8-hour

area even if a lapse is occurring in another state of the area. This independence in a multistate area applies as long as all states are using 1-hour budgets to determine conformity. 

For these Scenario 2 8-hour areas, each state can choose either of two versions of the

budget test:

• the budget test using the subset or portion of existing adequate or approved 1-hour

budgets that cover the 8-hour area within its state, where applicable and when such

portion can be appropriately identified (§93.109(e)(2)(ii)(A)); or

• the budget test using the existing adequate or approved 1-hour budgets for the

portion of the 1-hour area within its state, however in this case any additional

emissions reductions needed to pass the budget test must come from within that

state’s portion of the 8-hour area (§93.109(e)(2)(ii)(B)).
page 34

Scenario 3 Areas Within One State

14. Q. How is conformity demonstrated in a Scenario 3 area located entirely within one state,

when the 1-hour SIP establishes budgets that apply to the entire 1-hour area?

A. In this case, the conformity rule requires that the MPO or MPOs must work together

to apply the 1-hour budgets to the portion of the 8-hour area covered by them. An 8-hour

area whose boundary is larger than the 1-hour area boundary includes one or more new

counties that were not covered by the 1-hour standard. According to §93.109(e)(2)(iii),

conformity can be determined for the 1-hour area by using the 1-hour budgets for that

portion of the 8-hour area covered by them, plus the interim emissions test(s) for either:

• the remaining portion of the 8-hour area (the new county or counties), or 

• the entire 8-hour area.

In Figure 8 below, the budget test must be used for the gray portion of the area, and the

interim emissions test either for the white portion of the 8-hour area, or the entire 8-hour

area.
page 35

15. Q. How is conformity demonstrated in a Scenario 3 area located entirely within one state,

when the 1-hour SIP establishes subarea budgets that apply for each MPO? 

A. As described in Part 3, Q& As 5 - 7, and in Q & As 6 - 8 of this part, each MPO can

develop its own regional emissions analysis and conformity determination for its plan and

TIP, as long as all of the other MPOs in the area have a conforming plan and TIP in place

The twist for a Scenario 3 area is that there is a portion of the 8-hour area that is not

covered by 1-hour budgets. For this portion of the 8-hour area, a regional emissions

analysis using the interim emissions test(s) must be done for either: 

< the part of the 8-hour area not covered by 1-hour budgets, or

< the entire 8-hour area. 

As addressed in Q & A 7 of this part, for the initial conformity determinations under the 8-

hour standard, each MPO can determine conformity for its own plan and TIP and DOT

will wait to receive a conformity determination for each MPO before making its

conformity determination for the plans and TIPs in the area.

In Figure 9, above, MPOs A, B, C, and D can develop conformity determinations for just

their own plans and TIPs using their 1-hour subarea budgets. The regional emissions

analysis for Part E must be done using the interim emissions test(s), according to

§93.109(e)(2)(iii)(B) of the conformity rule. Part E may be a donut area or may have its

own MPO. If Part E is a donut area, per §93.105(c)(3) of the rule, the parties involved in

interagency consultation must discuss which agency will be responsible for Part E’s

regional emissions analysis, and for what geographic area it will be done. DOT would

wait until it had conformity determinations for all MPO plans/TIPs and the donut area

before making its initial conformity determinations for the 8-hour standard.
page 36 

Scenario 3 Multi-State Areas 

16. Q. How is conformity demonstrated in multi-state Scenario 3 areas, where all of the states 

have their own separate 1-hour SIP budgets? 

A. As described above, conformity determinations can continue to be made independently 

in each state that has separate 1-hour budgets, as long as all states in the area use their 

respective 1-hour budgets for their 8-hour conformity determinations. In addition, if the 

8-hour boundary in a state is larger than the 1-hour boundary in that state, the interim 

emissions test(s) must be met for either: 

• the portion outside the 1-hour boundary and inside the 8-hour boundary in that 

state, 

• that state’s entire portion of the 8-hour nonattainment area, or 

• the entire multi-state 8-hour area.7 

The provision of the rule that requires the interim emissions test(s) in Scenario 3 areas, 

§93.109(e)(2)(iii)(B), could apply to any of these three geographic choices. 

For example, in Figure 10 below, an 8-hour nonattainment area includes parts of three 

states. The 8-hour boundary in States A and B is unchanged from the 1-hour boundary, 

but the 8-hour boundary in State C is larger. States A, B, and C can continue to 

determine conformity independently from one another for the 8-hour standard as follows: 

• States A and B would determine conformity by meeting their 1-hour budgets. 

• State C would determine conformity by meeting its 1-hour budgets, plus the 

interim emissions test(s) either for: 

< the portion in State C not covered by the 1-hour budgets (in Figure 10, the 

white portion inside the bold line), 

< the entire portion of the 8-hour area in State C, or 

< the entire multi-state area (see footnote 7). 

7

Though the interim emissions test(s) could be done for the entire 8-hour nonattainment 

area under the final rule, as explained in the preamble (69 FR 40023), “doing so may not allow 

each MPO in this example to develop transportation plans and TIPs and conformity 

determinations independently.” Please consult with EPA and DOT to discuss the implications for 

all states before choosing this option. 
page 37

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

one of the states has its own 1-hour SIP budgets? 

A. Consistent with Clean Air Act section 176(c), EPA interprets §93.109(e)(2)(iii) of the

conformity rule to mean that a state can determine conformity completely independently,

even if it is the only state in the 8-hour area that has 1-hour budgets. If one state has 1-

hour budgets and the 8-hour area is a two-state area, then both states can determine

conformity on their own:

• the state with the 1-hour budgets would continue to use them for 8-hour

conformity;

• the state without budgets would use the interim emissions test(s). 

In Figure 11 below, each state can determine conformity for its own portion of the 8-hour

area, even though State B does not have 1-hour budgets.

However, if the 8-hour area was a three-state area and only one state had 1-hour budgets,

only the state with the budgets could determine conformity on its own. The other two

states would determine conformity for the 8-hour standard together using the interim

emissions test(s).
page 38 

Scenario 3 – General 

18. Q. What are the special issues that the interagency consultation process should consider 

in Scenario 3 areas? 

A. The interagency consultation process is of key importance in these areas. Because the 

8-hour area is larger than the 1-hour area, one or more planning agencies previously not 

involved in conformity may become part of the interagency process. These planning 

agencies need to be included in the decision-making process for the area. 

Through the interagency consultation process as required by §93.105 of the conformity 

rule, the involved parties must decide: 

• whether to apply the interim emissions test(s) to the entire 8-hour area (or in a 

multi-state area where one or more of the states have 1-hour budgets, to one 

state’s entire portion of the area) or just the portion not covered by the 1-hour 

budgets; 

• 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 permitted to 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 §§93.118(d)(2) and 93.119(g), as described below. 

Scenario 4 Areas Within One State 

19. Q. How is conformity done in a Scenario 4 area, when 1-hour budgets apply to the entire 

1-hour area, that is, the SIP does not establish subarea budgets? 

A. It may be possible to use the budgets from the 1-hour SIP, if the SIP includes 

emissions by county and it is possible to determine which portions of the 1-hour budgets 

apply to the 8-hour area. In this case, the 8-hour area would show conformity in a manner 

similar to a Scenario 3 area. It would use: 

• the relevant portion of the 1-hour budgets for the portion of the 8-hour area where 

it has them, plus 

• the interim emissions test(s), either for: 

< the remaining portion of the 8-hour area, or 

< the entire 8-hour area. 
page 39

8

 This statement does not preclude agencies from developing a reasonable way to utilize

the 1-hour budgets, via the interagency consultation process where possible. The final conformity

rule requires the use 1-hour budgets where ever it is appropriate and possible.

For example, in Figure 12 below, if it is possible to determine what portion of the 1-hour

budgets apply for the portion of the 1-hour area that is now inside the 8-hour area

boundary, the area would use:

• the budget test, for that portion of the 8-hour area that has them (as indicated by

the arrow in Figure 12), and 

• the interim emissions test(s) must be met for either:

< the part of the 8-hour area not covered by budgets – n Figure 12, the

portion shaded with the pattern, or

< the entire 8-hour area. 

However, it may not be possible for the 8-hour area to use the 1-hour budgets at all. This

outcome would occur, for example, if 1-hour SIP does not include an emissions inventory

by county. It could also occur if the 8-hour boundary includes and excludes portions of

counties instead of entire counties. The interagency consultation process would be used

to discuss use of 1-hour budgets in Scenario 4 areas. When such cases occur, a Scenario

4 area would determine conformity using the applicable interim emissions test(s) for the

entire area.8

Scenario 4 Multi-State Areas

20. Q. How does a multi-state Scenario 4 area determine conformity when the 1-hour SIPs

have separate budgets that apply to each state?

A. As described above, multi-state Scenario 4 areas are a unique case. Where each state

has separate 1-hour budgets that apply only to its portion of the nonattainment or

maintenance area, each state in a multi-state Scenario 4 area can operate entirely

independently. Where a state’s portion can use its 1-hour budgets, it must use them

i
page 40 

according to §93.109(e)(2)(iv) of the rule. Any portion of a state’s area not covered by 

the budgets would have to be included in an interim emissions test(s), for: 

• that part not covered by 1-hour budgets, 

• the state’s entire portion of the 8-hour area, or 

• the entire 8-hour area. 

The consultation process would be used to determine which test option is selected in 

Scenario 4 areas. 

21. Q. How is the regional emissions analysis done in a multi-state Scenario 4 area, where 

only one of the states has its own 1-hour SIP budgets? 

A. EPA interprets §93.109(e)(2)(iv) to mean that if any state in the 8-hour area has 1-

hour budgets, that state can determine conformity completely independently from the 

other states in the 8-hour area. The state or states that have 1-hour budgets would 

continue to use them or portions of them as appropriate, to the extent possible, for their 8-

hour regional emissions analysis and conformity determination. The state or states 

without 1-hour SIP budgets would use the interim emissions test(s) for 8-hour conformity; 

if there is more than one state in the area without 1-hour budgets, these states would 

determine conformity together. 

22. Q. What are special issues that the interagency consultation process should consider in 

Scenario 4 areas? 

A. As in Scenario 3 areas, the interagency consultation process is of key importance in 

Scenario 4 areas. Where an 8-hour area partially overlaps a 1-hour area, one or more 

MPOs may no longer have to determine conformity, and one or more new MPOs may 

become part of the interagency process. All MPOs in the 8-hour 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 as required by §93.105 of the conformity 

rule, the involved parties must decide: 

• whether to apply the interim emissions test(s) to the entire area (or in a multi-state 

area, to one state’s portion of the area) or just the portion not covered by the 1-

hour budgets; 

• 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 permitted to select only one test; 

and 
page 41 

• 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 §§93.118(d) and 93.119(e) of the rule, as described below. 

General Implementation of Final Rule 

23. Q. What precursors must be examined in 8-hour areas with 1-hour budgets? 

A. As described in the preamble to the July 1, 2004, final transportation conformity rule 

the regional emissions analyses for ozone areas must address the ozone precursors 

nitrogen oxides (NOx) and volatile organic compounds (VOC) (§93.102(b)(2)(i)). In 

cases where budgets are used, conformity is demonstrated with the budget test for 

adequate and approved NOx and VOC budgets (§93.118). In all cases where areas use 

the interim emissions test(s), both precursors must be analyzed unless EPA issues a NOx 

waiver for the 8-hour standard for an area under Clean Air Action section 182(f). These 

requirements are consistent with the conformity rule to date, although the July 2004 final 

rule moves these provisions to §93.119(f) due to reorganization of §93.119. Areas must 

also complete the interim emissions test(s) for NOx if the only SIP available is a 

reasonable further progress SIP for either the 1-hour or 8-hour standard that contains a 

budget for VOCs only (e.g., a 15% SIP). See §93.109(e)(3) of the final rule for further 

information. 

24. Q. How is the budget test generally implemented in 8-hour areas with 1-hour budgets? 

A. The budget test requirements in §93.118 for 8-hour areas will be generally 

implemented in the same manner as in 1-hour areas, with a few exceptions. First, as 

described above, the geographic area covered by the 8-hour standard may be different 

than that covered by the 1-hour standard and SIP budgets in some cases. Second, the 

years for which regional modeling is required (i.e., analysis years) may differ. 

Areas that use 1-hour budgets for their 8-hour conformity determinations will need to 

determine the modeling analysis years that apply for the 8-hour standard per §93.118(d). 

Under this section, a modeling analysis must be completed for: 

• the last year of the transportation plan, 

• the attainment year for the relevant pollutant and standard, and 

• an intermediate year(s) such that analysis years are not more than 10 years apart. 

The attainment year analysis is to be for an area’s attainment year for the 8-hour standard, 

which probably will be different than the attainment year under the 1-hour standard. The 
page 42 

area must then calculate emissions in the analysis years from the planned transportation 

system. 

Once modeling is completed per §93.118(d)(2), 8-hour areas using 1-hour SIPs will also 

demonstrate consistency with the 1-hour budgets according to §93.118(b), except for 

cases where it is determined that 1-hour budgets are not appropriate through the 

consultation process as described above and in §93.109(e)(2)(v) of the conformity rule. 

According to §93.118(b) the July 1, 2004, final rule, consistency with 1-hour budgets 

must be shown for: 

• all 1-hour budget years that are within the timeframe of the transportation plan, 

• the 8-hour attainment year, 

• the last year of the plan, and 

• an intermediate year(s) so that all years are not more than 10 years apart. 

Emissions projected for each analysis year must be within the budgets in the 1-hour SIP 

from the most recent prior year. Interpolation can be used between analysis years for 

demonstrating consistency with budgets, just as has been done under the 1-hour standard. 

For example, suppose an area designated nonattainment for the 8-hour ozone standard 

with an 8-hour attainment date of 2010 has the following 1-hour budgets: 

• 2005 rate-of-progress (ROP) budgets for NOx and VOCs, 

• 2007 ROP budgets for NOx and VOCs, and 

• 2007 attainment budgets for NOx and VOCs. 

By 2005, this area would determine conformity for its 2005-2025 transportation plan and 

its TIP, and the conformity determination would be accomplished as follows: 

• 2005 budget test, using the 2005 ROP budgets; 

• 2007 budget test, using both 2007 ROP and attainment budgets; 

• 2010 budget test, using the 2007 attainment budgets

9

; 

• 2020 budget test,10 using the 2007 attainment budgets; and 

• 2025 budget test, using the 2007 attainment budgets. 

As described in §93.118(d)(2), emissions for the year 2005 could be generated with a 

regional emissions analysis, or could be interpolated if the area has run a regional 

9

EPA has previously interpreted that only attainment budgets apply beyond the attainment 

year, in cases where ozone areas also have budgets for ROP SIPs. 

10The year 2020 is chosen for this example, but any year from 2015 through 2019 would 

also be acceptable for the interim year analysis. 
page 43 

emissions analysis for an earlier year. Emissions for the year 2007 could also be 

interpolated or the area could choose to model emissions for this year. A regional 

modeling analysis must be done for the year 2010 (the 8-hour attainment year), any year 

between 2015 and 2020 for the intermediate year (in this example, 2020 is the 

intermediate year), and the year 2025 (the last year of the transportation plan) as required 

by §93.118(d)(2). 

As stated above, once adequate or approved 8-hour budgets are established for a given 

precursor, the budget test would be completed with only the 8-hour budgets for that 

precursor, rather than the 1-hour budgets. 

25. Q. Where 8-hour areas have to use both the budget test and the interim emissions test(s), 

what analysis years would be chosen? 

A. As described in the July 2004 final rule, there will be cases in Scenario 3 or 4 areas 

where both the budget and interim emissions tests are used. Sections 93.118 and 93.119 

of the conformity rule cover the criteria and procedures for the budget test and the interim 

emissions tests, respectively. Each of these sections define the analysis years that must be 

examined in the particular test. 

In the budget test, the years that must be analyzed (§93.118(d)(2)) are: 

• the 8-hour attainment year, 

• the last year of the transportation plan, and 

• an intermediate year or years as necessary, so that analysis years are no more than 

ten years apart. 

In the interim emissions tests, the years that must be analyzed (§93.119(g)) are: 

• a year no more than five years in the future (from the year in which the conformity 

determination is made) 

• the last year of the transportation plan, and 

• an intermediate year or years as necessary, so that analysis years are no more than 

ten years apart. 

The interagency consultation process can be used to choose analysis years that meet the 

requirements of both §§93.118 and 93.119 so that the number of analysis years is 

minimized. For example, consider a Scenario 3 area in one state that is classified as 

moderate for the 8-hour standard that has 1-hour budgets for the years 2005 and 2007. 

This area needs to use both the budget and interim emissions tests to determine conformity 

for the 8-hour standard, because there is a portion of the area that is not covered by the 1-

hour budgets. The plan covers the years 2005 through 2025 and the conformity 

determination will be made in the year 2005. This area could examine the following 

analysis years in its 8-hour conformity determination: 
page 44 

• 2010, which fulfills the §93.118 requirement to analyze the 8-hour attainment year, 

and the §93.119 requirement to analyze a year no more than five years in the 

future; 

• 2015, which fulfills the requirement in both rule sections to analyze an intermediate 

year so that analysis years are no more than 10 years apart; and 

• 2025, which fulfills the requirement in both rule sections to analyze the last year of 

the plan. 

In addition, the rule requires that the portion of the area covered by the 1-hour budgets 

must also demonstrate consistency with the budgets for the years 2005 and 2007. 

Consistency can be demonstrated using interpolation for a year between two analysis years 

as described in §93.118(d)(2) of the conformity rule. In this example, the area could do a 

regional emissions analysis for 2005 and interpolate emissions for 2007 using the 2005 and 

2010 analyses. Alternatively, the area could interpolate 2005 and 2007 emissions by using 

an analysis for a year before 2005 done for model validation purposes, if such a year is not 

more than 10 years earlier than 2010 (so that analysis years are no more than 10 years 

apart). 

In this example, the budget test and interim emissions test requirements would then be 

satisfied as follows: 

• 2005: budget test, using the 2005 budgets 

• 2007: budget test, using the 2007 budgets 

• 2010: budget test, using the 2007 budgets 

and interim emissions test(s) for 2010 

• 2015: budget test, using the 2007 budgets 

and interim emissions test(s) for 201511 

• 2025: budget test, using the 2007 budgets 

and interim emissions test(s) for 2025 

As described in §93.109(e)(2)(iii) of the July 1, 2004, final rule, the regional emissions 

analysis for the budget test in Scenario 3 would cover the 1-hour area portion of the 8-

hour area (i.e., the portion covered by the 1-hour budgets). The regional analyses for the 

interim emissions tests in an area located within a single state would cover either the 

portion of the 8-hour area not covered by the 1-hour budgets, or the entire 8-hour area. 

[answer continues on the next page] 

11The year 2015 is chosen for this example, but any year between 2016 and 2020 would 

also be acceptable for the interim year analysis. 
page 45 

The regional analyses for the interim emissions tests in a multi-state area would cover 

either the portion of a state’s 8-hour area not covered by its 1-hour budgets, or a state’s 

entire 8-hour area.12 

12The July 1, 2004, final rule also provides a third interim emissions test option for certain 

Scenario 3 multi-state areas: the regional emissions analysis could cover the entire multi-state 

area. Please consult EPA before choosing this option to discuss its implications.