Guidance for the Use of Latest Planning
Assumptions in Transportation Conformity
Determinations
Revision to January 18, 2001 Guidance
Memorandum
United States
Environmental Protection
Agency
US. Department of Transportation
December 2008
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Guidance for the Use of Latest Planning
Assumptions in Transportation Conformity
Determinations
Revision to January 18, 2001 Guidance
Memorandum
Transportation and Regional Programs Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
Office of Natural and Human Environment
Federal Highway Administration
U.S. Department of Transportation
Office of Planning and Environment
Federal Transit Administration
U.S. Department of Transportation
EPA420-B-08-901
December 2008
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Table of Contents
Page
Executive Summary 1
Section 1: Introduction 2
1.1 Why are EPA and DOT providing this guidance now?
1.2 What is transportation conformity?
1.3 What conformity requirements are covered by this guidance?
1.4 What latest planning assumption requirements apply in my nonattainment or
maintenance area?
1.5 Who can I contact for more information?
1.6 Does this guidance create any new requirements?
Section 2: Latest Planning Assumption Requirements 6
2.1 What are the conformity requirements for use of latest planning assumptions?
2.2 What do we mean by "latest" planning assumptions?
2.3 When should planning assumptions be updated? What process should be used
for updates?
2.4 What vehicle registration assumptions must be used in emissions modeling for
conformity determinations? What process should be used to update these
assumptions?
2.5 If a state government or other agency collects vehicle registration data on a
regular basis, should the most recent year of collected data be considered the
"latest" planning assumptions for the current conformity determination?
2.6 What are the planning assumption requirements for SIP development, and how
do they relate to the conformity rule's requirements?
2.7 What if the assumptions used in a submitted or approved SIP are not the most
current and best information for conformity determinations?
2.8 What are the requirements for periodic emissions inventory updates, and how do
they relate to the conformity rule's requirements for latest planning assumptions?
2.9 Are there any assumptions used in conformity analyses that must be consistent
with those in the SIP?
2.10 What are the requirements for taking credit in conformity analyses for approved
SIP control measures, such as I/M programs and TCMs? What should be
considered when determining the latest planning assumptions in conformity
regarding the implementation of approved SIP control measures?
2.11 Can an area that does conformity for several different pollutants rely on different
planning assumptions in its conformity determination?
2.12 Does a revision in latest planning assumptions trigger a new conformity
determination?
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2.13 Can an MPO rely on a previous regional emissions analysis even if planning
assumptions have changed?
2.14 How do the latest planning assumption requirements apply to project-level
conformity determinations and hot-spot analyses?
Section3: Implementation of the
Latest Planning Assumption Requirements 17
3.1 How should state and local agencies define the "time the conformity analysis
begins?"
3.2 To support a valid conformity determination, what planning assumption
information should be documented?
3.3 If new data becomes available after the analysis begins, should it be included in
the conformity determination?
3.4 Must an area wait to start the conformity analysis until anticipated changes in
planning data become available?
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Executive Summary
The Clean Air Act requires that transportation investments be based on the most
recent information that is available in order to protect public health over the long-term.
As such, conformity determinations must be based upon the most recent planning
assumptions in force at the time the conformity analysis begins (40 CFR 93.110(a)).
The Environmental Protection Agency (EPA) and Department of Transportation (DOT)
encourage state and local agencies to review and update their planning assumptions
regularly. Areas are strongly encouraged to review and update planning assumptions at
least every five years, especially population, employment, and vehicle registration
assumptions. Areas with network-based travel models should review their assumptions
and data used in model validation through the consultation process, and newer
assumptions and data must be used whenever available. Conformity determinations
that are based on assumptions that are older than five years should include written
justification for not reviewing and updating assumptions at least every five years. For
areas where updates are appropriate, the conformity determination should include an
anticipated schedule for updating assumptions for future conformity determinations. Air
quality and transportation agencies should use the consultation process to ensure that
the latest available planning assumptions are used in conformity determinations and
state implementation plan (SIP) development.
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Section 1: Introduction
1.1 Why are EPA and DOT providing this guidance now?
This update is necessary because the July 1, 2004 final conformity rule changed
the requirements regarding the use of the latest planning assumptions (69 FR 40052-
40056). Some examples of planning assumptions include population, employment, and
vehicle fleet information. This guidance supersedes the January 18, 2001 guidance
memorandum1 to address changes in the July 2004 conformity rule. All other aspects
related to conformity requirements and SIP development are consistent with the 2001
guidance.
In the July 2004 conformity rule, EPA changed 40 CFR 93.110(a) to allow a
conformity determination to be based on the latest planning assumptions in force at the
time the conformity analysis begins, rather than at the time of DOT'S conformity
determination2. EPA changed this provision so it is more workable for implementers
while remaining consistent with Clean Air Act requirements. Allowing conformity
determinations based on the latest information available at the time the conformity
analysis begins provides certainty for implementers and is a reasonable approach to
ensuring that conformity determinations are based on accurate and available
information.
EPA and DOT are issuing this guidance jointly to clarify our expectations for
implementing the transportation conformity rule's latest planning assumptions
requirements. This guidance also reiterates EPA's expectations for using latest
planning assumptions in the development of motor vehicle emissions budgets in SIPs.
1.2 What is transportation conformity?
Transportation conformity is required under Clean Air Act section 176(c) (42
U.S.C. 7506(c)) to ensure that federally supported highway and transit project activities
are consistent with ("conform to") the purpose of the SIP. Under this statute, conformity
to the purpose of the SIP means that transportation activities will not cause new air
quality violations, worsen existing violations, or delay timely attainment of the relevant
national ambient air quality standards. EPA's transportation conformity rule (40 CFR
Parts 51 and 93) establishes the criteria and procedures for determining whether
transportation plans, transportation improvement programs (TIPs), and projects conform
to the SIP. Transportation conformity applies to areas that are designated
nonattainment, and those redesignated to attainment after 1990 ("maintenance areas")
1 "Use of Latest Planning Assumptions in Conformity Determinations," memorandum from Robert
Perciasepe, Assistant Administrator for EPA's Office of Air and Radiation, Kenneth Wykle, FAA
Administrator and Nuria Fernandez, FTA Acting Administrator to FHWA Division Administrators, Federal
Lands Highway Division Engineers, FTA Regional Administrators, and EPA Regional Administrators,
Region I-X, January 18, 2001.
2 It is important to note that in certain situations, the previous requirements still apply. See Question 1.4
for further details.
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for transportation-related criteria pollutants: carbon monoxide, ozone, nitrogen dioxide,
PM2.5, and PMi0.
1.3 What conformity requirements are covered by this guidance?
This guidance document clarifies the implementation of the latest planning
assumption requirements in 40 CFR 93.110, which must be met at the time conformity
analysis begins as described later in this guidance. There are other transportation
conformity requirements that are not covered by the latest planning assumption
requirements that continue to be required to be met on the date of DOT'S conformity
determination.
EPA discussed some examples of requirements that are not considered part of
latest planning assumption requirements in the preamble to the July 1, 2004, final rule
(69 FR 40054-40055). For example, DOT'S conformity determination must be based on
whatever adequate or approved SIP motor vehicle emissions budgets apply at that time,
even if such budgets became available after the MPO's conformity determination (40
CFR 93.109 and 93.118). In addition, DOT'S conformity determination must be based
on a regional emissions analysis that accurately reflects control measures in the SIP,
transportation plan/TIP, or through written commitments (40 CFR 93.122(a)(1)-(4)), as
described further in Question 2.10.
1.4 What latest planning assumption requirements apply in my nonattainment or
maintenance area?
The latest planning assumption requirements for a conformity determination in a
given nonattainment or maintenance area can vary depending upon whether a state has
an EPA-approved conformity SIP3, and if so, when it was approved:
• If a state does not have an approved conformity SIP or if it has an approved
conformity SIP based on the July 2004 final rule, transportation planners and DOT
are required to meet the current conformity rule's requirement (40 CFR 93.110(a))
that latest planning assumptions be determined at the time the conformity
analysis begins.
• If a state has an approved conformity SIP based on the previous conformity rule,
transportation planners and DOT are required to meet that previous requirement.
3 A conformity SIP contains the state's criteria and procedures for interagency consultation. Unlike a
reasonable further progress SIP, an attainment demonstration, or maintenance plan, a conformity SIP
does not contain motor vehicle emissions budgets, emissions inventories, air quality demonstrations, or
control measures. A conformity SIP can be developed as a state rule, a memorandum of understanding
(MOD), or a memorandum of agreement (MOA). In general, once approved, the conformity SIP governs
the conformity process instead of the federal conformity rule for any provisions included in the conformity
SIP.
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In such a case, conformity determinations would be required to be based on the
latest planning assumptions available at the time of DOT'S final conformity
determination.
Section 51.390(b) of the conformity rule requires conformity determinations in a
given nonattainment or maintenance area to meet any applicable requirements in an
EPA-approved conformity SIP. Any out-dated requirements, such as the previous rule's
latest planning assumptions requirements, would no longer apply when the state either
withdraws or updates such requirements, and EPA approves the revised conformity
SIP. Section 3 of today's guidance document does not apply to areas operating under
approved conformity SIPs that include the previous latest planning assumptions
requirements.
1.5 Who can I contact for more information?
For specific questions concerning a particular nonattainment or maintenance
area, please contact the transportation conformity staff person responsible for your state
at the appropriate EPA regional office, Federal Highway Administration (FHWA) division
office or Federal Transit Administration (FTA) regional office:
• A listing of EPA regional offices, the states they cover, and contact information
for conformity staff can be found at the following website:
http://www.epa.gov/otaq/stateresources/transconf/contacts.htm,
• Contact information for FHWA division offices can be found at:
http://www.fhwa.dot.qov/field.html, and
• Contact information for FTA regional offices can be found at:
http://www.fta.dot.gov/reqional offices.html.
General questions about this guidance can be directed to:
• Patty Klavon of EPA's Office of Transportation and Air Quality,
klavon. pattv@epa.gov or at (734) 214-4476,
• Cecilia Ho of FHWA's Office of Natural and Human Environment,
cecilia.ho@dot.qov or at (202) 366-9862, or
• Abbe Marner of FTA's Office of Planning and Environment,
abbe.marner@dot.gov or at (202) 366-4317.
Readers can also find this guidance document, the complete transportation
conformity regulation, and other materials on the EPA's website at:
http://www.epa.gov/otaq/stateresources/transconf/conf-reqs.htm
1.6 Does this guidance create any new reguirements?
No, this guidance is based on the requirements for latest planning assumptions
contained in Clean Air Act section 176(c) and 40 CFR 93.110, and does not create any
new requirements. This guidance merely explains how to implement the latest planning
assumption provisions and related requirements.
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The statutory provisions and the EPA regulations described in this document
contain legally binding requirements. This document is not a substitute for those
provisions or regulations, nor is it a regulation itself. Thus, it does not impose legally
binding requirements on EPA, DOT, states, or the regulated community, and may not
apply to a particular situation based upon the circumstances. EPA and DOT retain the
discretion to adopt approaches on a case-by-case basis that may differ from this
guidance, but still comply with the statute and conformity and SIP regulations. Any
decisions regarding a particular area's use of the latest planning assumptions will be
made based on the statute and regulations, after appropriate public input and
rulemaking procedures where applicable. This guidance may be revised periodically
without public notice.
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Section 2: Latest Planning Assumption Requirements
2.1 What are the conformity requirements for use of latest planning assumptions?
Section 176(c)(1)(B)(iii) of the Clean Air Act states that "[t]he determination of
conformity shall be based on the most recent estimates of emissions, and such
estimates shall be determined from the most recent population, employment, travel, and
congestion estimates as determined by the MPO or other agency authorized to make
such estimates." The Clean Air Act requires that transportation investments be based
on the most recent information that is available, in order to protect public health over the
long-term.
The conformity regulations at 40 CFR 93.110 provide the requirements for using
the latest planning assumptions in transportation conformity determinations. The
requirements apply to all assumptions used in demonstrating conformity, including
assumptions that are used in transportation demand and emissions modeling.
Examples of assumptions are land use, vehicle age and fleet mix, and the most recent
information regarding the implementation of control measures in approved SIPs (e.g.,
inspection and maintenance (I/M), fuels programs, and transportation control
measures). Section 93.110(a) of the transportation conformity rule requires conformity
determinations to be based on the "most recent planning assumptions in force at the
time the conformity analysis begins." Section 93.110(a) of the conformity rule also
requires that, "New data that becomes available after an analysis begins is required to
be used in the conformity determination only if a significant delay in the analysis has
occurred, as determined through interagency consultation." See Section 3 of this
guidance for further discussion on when a "conformity analysis begins," and for what
may be considered "a significant delay."
As applicable, specific latest planning requirements are further outlined in 40
CFR 93.110(b)-(f):
"(b) Assumptions must be derived from the estimates of current and future
population, employment, travel, and congestion most recently developed by the
MPO or other agency authorized to make such estimates and approved by the
MPO. The conformity determination must also be based on the latest
assumptions about current and future background concentrations.
(c) The conformity determination for each transportation plan and TIP must
discuss how transit operating policies (including fares and service levels) and
assumed transit ridership have changed since the previous conformity
determination.
(d) The conformity determination must include reasonable assumptions about
transit service and increases in transit fares and road and bridge tolls over time.
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(e) The conformity determination must use the latest existing information
regarding the effectiveness of the transportation control measures (TCMs) and
other implementation plan measures which have already been implemented.
(f) Key assumptions shall be specified and included in the draft documents and
supporting materials used for the interagency and public consultation required by
§93.105."
EPA, DOT, and state and local transportation and air quality agencies participate
in the interagency consultation process to review and comment on assumptions (40
CFR 93.105), and the latest planning assumption requirements must be met before
DOT can make a conformity determination (40 CFR 93.109(b)).
As assumptions are expected to change over time, it is important that state, local,
and federal transportation and air quality planners evaluate on a regular basis existing
assumptions and new information as it becomes available. Conformity determinations
that are based on assumptions that are older than five years should include written
justification for not using more recent information. See Question 2.3 for more details on
when latest planning assumption updates are needed.
2.2 What do we mean by "latest" planning assumptions?
Using the "latest" planning assumptions means that the conformity determination
is based on the most current information that is available to state and local planners
(e.g., the MPO or other agency can obtain the information from another agency, the
information is appropriate for the current conformity determination, the information is
readily transferable for use in transportation and/or emissions modeling, etc.).
Latest planning assumptions must be derived from the population, employment,
travel, and congestion estimates that have been most recently developed by the MPO
(or other agency authorized to make such estimates), and approved by the MPO (40
CFR 93.1 10(b)). Once approved, these estimates must be used for determining the
latest planning assumptions (40 CFR 93.1 10(a)). In areas using network-based travel
models, scenarios of land development and use must be consistent with the future
transportation system for which emissions are being estimated, and the distribution of
employment and residences for the transportation system must be reasonable (40 CFR
The interagency consultation process must be used to determine which planning
assumptions are considered the latest and best assumptions for conformity
determinations. The conformity rule specifically requires that the interagency
consultation process be used to evaluate and choose assumptions to be used in
conformity analyses (40 CFR 93.105(c)(1)(i)).
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The consultation process should be used to evaluate assumptions for quality and
accuracy as needed prior to use in conformity. Whenever Highway Performance
Monitoring System (HPMS) data is used for current and future years in conformity
analyses, the most recently available HPMS estimates of vehicle miles traveled (VMT)
must be used (40 CFR 93.110(a)). Historical trends and other factors should be
considered as a primary source of information from which planning assumptions should
be evaluated (e.g., population, employment). If assumptions are used that contradict
historical trends, the conformity determination should include an explanation regarding
why the assumptions are appropriate. This explanation should be included when the
conformity determination is provided for public comment. The consultation process
should not be used to unduly delay or exclude the use of new information or to
selectively employ it for the convenience of the conformity process.
Areas that rely on the U.S. Census for certain planning assumptions must use
the most recent estimates available from the Census Bureau (40 CFR 93.110(a)).
Areas that are using assumptions based on data collected through local or state
surveys or other mechanisms should use the consultation process to determine whether
older state or local data is more appropriate than the most recently available U.S.
Census.
2.3 When should planning assumptions be updated? What process should be used
for updates?
EPA and DOT encourage nonattainment and maintenance areas to review and
update their planning assumptions on a regular basis. Although regular updates of
assumptions are not required by the transportation conformity rule, areas are strongly
encouraged to review and update planning assumptions at least every five years,
especially for population, employment, and vehicle registration assumptions, or to justify
in the conformity determination why planning assumptions have not been reviewed and
updated at least every five years.
As planning assumptions are expected to change over time, it is important that
state, local, and federal transportation and air quality planners evaluate, on a regular
basis, existing assumptions and new information as it becomes available. This may be
especially important in areas that are experiencing higher population and employment
growth than is reflected in current planning assumptions. Conformity determinations that
are based on information that is older than five years should include written justification
for not using more recent information. For areas where future updates are determined
to be necessary, the conformity determination should include an anticipated schedule
for updating assumptions.
Planning assumptions must be reviewed through the interagency consultation
process to determine whether they are adequate for conformity purposes (see 40 CFR
93.105(c)(1)(i)). The review of latest planning assumptions typically occurs in
conjunction with transportation plan and TIP conformity determinations. The results of
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the review of the planning assumptions and consultation process would be documented
in the conformity determination. The interagency consultation process is also the forum
for evaluating and choosing assumptions that are used in conformity determinations in
isolated rural nonattainment and maintenance areas (40 CFR 93.105(c)(1)(vi)).
EPA and DOT should be proactively involved in the interagency consultation
process in all nonattainment and maintenance areas so that potential issues and
problems can be identified and addressed early on in the conformity process. If it is
determined through interagency consultation that certain planning assumptions need to
be updated, state and local transportation and air quality agencies should commit to a
schedule to update those assumptions for future conformity determinations. Different
schedules can be established for updating different assumptions. The level of
resources dedicated to updating assumptions may vary depending upon planning
priorities in a given area. State and local agencies can prioritize these updates along
with other planning needs. See below for specific information regarding our
expectations for vehicle registration assumptions.
Areas required to use network-based travel models for conformity purposes
should also review their assumptions and data used in model development and
validation through the consultation process, and the latest assumptions and data must
be used whenever available (40 CFR 93.110). Since emission estimates are sensitive
to vehicle speed changes, EPA and DOT recommend that areas using network-based
travel models compare the speeds estimated in the validation year with speeds
empirically observed during the peak and off-peak periods. The significant sensitivity of
emissions to highway speeds emphasizes the need to monitor and maintain the ability
of the transportation model to provide accurate speed estimates. Nonattainment and
maintenance areas using network-based travel models are encouraged to establish
criteria for updating the observed speed data that are used to validate the speeds
predicted by the transportation model. The criteria should identify the schedule on
which speed data will be collected given the pace of growth in the urban area, the
magnitude of changes to the highway system, and any fundamental changes in speed-
related conditions such as a change in the federal or the state's maximum speed limit.4
2.4 What vehicle registration assumptions must be used in emissions modeling for
conformity determinations? What process should be used to update these
assumptions?
As stated above, MPOs must use the most recent vehicle registration data that is
available for conformity analyses at the time the conformity analysis begins (40 CFR
93.110(a)). State and local transportation and air quality agencies should make an
effort to obtain recent registration data files and should establish a schedule for
updating local vehicle registration data on a regular basis.
4 In December 1995, the federal speed limit law was changed to remove the mandatory 55 mph speed
limit and allow states to set limits using their own discretion.
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The composition of vehicle fleets can vary significantly over time and from area
to area. It is critical for areas to use the interagency consultation process to examine
new vehicle registration data (i.e., vehicle type and age) as it becomes available and
consider whether the current data and assumptions are still appropriate for conformity
purposes. It is especially important for areas to update assumptions if the
characteristics of the fleet have significantly changed from the assumptions that are
currently being used for conformity.
As a general rule, local data should be used whenever available. If local data is
not currently available and cannot reasonably be made available for use in impending
conformity determinations, areas may rely on the national defaults related to vehicle
registration data in the latest EPA-approved motor vehicle emissions factor model.
However, areas should explore whether more recent local vehicle registration data can
be made available in a useable format for the next conformity determination. Once
such data becomes available before a conformity analysis begins, it must be used in the
conformity analysis (40 CFR 93.110(a)). When EPA releases a new motor vehicle
emissions factor model and associated guidance for use in conformity determinations,
some areas will need to use the interagency consultation process to determine whether
older local data should be used instead of newer national defaults.
EPA also notes that the SIP process can be a valuable source for vehicle
registration data for conformity determinations, and many state and local air agencies
play a lead role in reviewing this type of data. Another example may be when the state
air agency has quality assured newer vehicle registration data from what is included in a
currently approved SIP.
2.5 If a state government or other agency collects vehicle registration data on a
regular basis, should the most recent year of collected data be considered the
"latest" planning assumptions for the current conformity determination?
Yes, if that information is available for conformity purposes at the time the
conformity analysis begins (40 CFR 93.110(a)). However, most state governments
collect information, such as vehicle registration data, on an annual basis for purposes
other than conformity. This data includes information about vehicle age and fleet mix,
for example, which are important inputs for emissions modeling. Although this
information may be sufficient for some state government purposes not related to air
quality (e.g., state tax or insurance purposes), the most recent year of collected raw
data may not necessarily be the best available information for use in the current
conformity analysis. Of course, if the latest state or local vehicle registration data has
been quality-assured and is being used for emissions modeling, then it must also be
considered the latest data for conformity (40 CFR 93.110(a)).
The interagency consultation process should be used to determine whether the
most recent vehicle registration data is available for conformity. State and local
transportation and air quality agencies should consider whether the data are accurate
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and appropriate for conformity purposes, as well as whether the data are readily
transferable for use in emissions modeling for the specific nonattainment or
maintenance area.
If the most recent vehicle registration data are not available for use in the current
conformity determination, the consultation process should be used to determine
whether such vehicle registration data should be reviewed and used for the next
determination. The conformity determination should include an explanation of why
recent state or local vehicle registration data was not considered available for
conformity purposes, if concerns are raised during the consultation or public
involvement processes. EPA and DOT recommend that if the new data can be quality
assured and/or formatted for emissions modeling purposes, it should be used.
2.6 What are the planning assumption requirements for SIP development, and how
do they relate to the conformity rule's requirements?
Motor vehicle emissions budgets in SIPs must be based on the most current
information available at the time that the SIP is developed (see Clean Air Act section
172(c)(3)). As such, planning assumptions, including VMT, socioeconomic variables,
and emissions modeling inputs (including vehicle registration by age and type) must be
based on the latest information available at the time that the SIP is developed and be
consistent with SIP inventory and emissions modeling requirements.
As stated in the July 2004 final rule, state and local agencies should consider the
availability of new planning assumptions when determining their conformity schedules
(69 FR 40054). The consultation process would be used to determine the most recent
planning assumptions available for SIP development, since the conformity rule provides
for such consultation in SIP development (40 CFR 93.105). If a new SIP budget is
found adequate or approved prior to the MPO or DOT'S conformity determination,
conformity to the new budget is required. In this case, transportation planners should
use the more recent planning assumptions that are in the new budget. State and local
air agencies should inform transportation agencies of new planning assumptions as
they become available.
Transportation planners are encouraged to review and comment on motor
vehicle emissions budgets as well as share more current assumptions with air quality
agencies so that they can be included in the SIP. This is especially important since air
quality and transportation agencies usually provide different types of planning
assumptions to SIP and conformity processes. For example, transportation planners
are more likely to have the latest VMT estimates for a given nonattainment or
maintenance area while air agencies are more likely to have the latest available vehicle
registration data. It is critical that transportation and air agencies exchange information
on a regular basis so that the latest assumptions are used in SIP and conformity
processes.
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2.7 What if the assumptions used in a submitted or approved SIP are not the most
current and best information for conformity determinations?
As described above, the Clean Air Act and conformity regulations require the
latest planning assumptions to be used in conformity determinations, even if they differ
from those used in the SIP (40 CFR 93.110(a)). In many cases, the MPO may have
developed more recent assumptions for the conformity process than those included in a
submitted or approved SIP. For example, the MPO may have adopted new population,
employment, and/or socioeconomic projections or updated transportation models since
the SIP was submitted. In this case, an MPO would use the latest planning
assumptions based on the newer projections and model improvements for conformity.
The interagency consultation process should be used to ensure that air quality and
transportation planning processes anticipate such changes in planning assumptions. It
is expected that planning assumptions in the conformity process will change over time
from those used in the SIP.
For further information, see the preamble to the July 1, 2004, final rule (69 FR
40053) and the November 24, 1993, final rule (58 FR 62210).
2.8 What are the requirements for periodic emissions inventory updates, and how do
they relate to the conformity rule's requirements for latest planning assumptions?
Clean Air Act section 172(c)(3) requires that periodic emissions inventories be
done in nonattainment areas. There are also specific requirements for periodic
inventories under individual subparts to part D of Title 1, such as section 182(a)(3) for
ozone and section 187(a)(5) for carbon monoxide (CO). According to Clean Air Act
section 172(c)(3), periodic inventory updates for SIPs must be based on the most
current information available at the time that the inventory is developed. Examples of
assumptions used in both inventory updates and conformity are VMT, socioeconomic
variables, and vehicle fleet characteristics. Although periodic inventory updates do not
establish motor vehicle emissions budgets, they can be a valuable source of more
recent and better planning assumptions for use in the conformity process.
Air quality and transportation agencies should work together to ensure that the
latest planning assumptions are used in SIP inventory updates and conformity
determinations. As discussed above, transportation planners should share more
current assumptions with air quality agencies so that they can be included in the SIP.
Air quality agencies should also provide more recent assumptions to transportation
planners for conformity determinations. The interagency consultation process required
by 40 CFR 93.105 should be used to determine whether the assumptions used in
periodic SIP inventory updates are more recent and better than the assumptions used
previously for conformity determinations.
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2.9 Are there any assumptions used in conformity analyses that must be consistent
with those in the SIP?
Yes. The transportation conformity rule (40 CFR 93.122(a)(6)) requires that
ambient temperatures in conformity analyses must be consistent with those used in the
SIP's motor vehicle emissions budgets. Other assumptions - or factors - that must be
consistent with those used in the SIP's motor vehicle emissions budget could also
include humidity, altitude, the fraction of travel in a hot stabilized engine mode and
annual mileage accumulation rates over the time frame of the transportation plan (40
CFR 93.122(a)(6)). These types of factors do not typically change in future years and
could significantly impact emissions; EPA generally believes that it is appropriate to
require such factors to be consistent between conformity analyses and the SIP budgets.
However, under certain circumstances, it may be appropriate to use alternative
factors instead of certain SIP assumptions, if it is determined through the interagency
consultation process that these factors should be modified. For example, such
modifications in these types of factors may be appropriate where additional or more
geographically specific information is incorporated or a logically estimated trend in such
factors beyond the period considered in the SIP is represented. EPA does not expect
changes in the SIP's factors to occur often, and they could only occur after consultation
among all local, state, and federal agencies. All planning assumptions used in a
conformity analysis must be documented in the conformity determination that is
released for public comment (40 CFR 93.105(e)); see the July 1, 2004, final rule for
further information (69 FR 40056).
2.10 What are the requirements for taking credit in conformity analyses for approved
SIP control measures, such as I/M programs and TCMs? What should be
considered when determining the latest planning assumptions in conformity
regarding the implementation of approved SIP control measures?
There are several conformity requirements that apply when reflecting approved
SIP control measures in conformity determinations. First, DOT'S conformity
determination must be based on a regional emissions analysis that reflects the actual
implementation of approved SIP control measures (40 CFR 93.122(a)). For example,
section 93.122(a)(2) of the conformity rule states:
"The emissions analysis may not include for emissions reduction
credit any TCMs or other measures in the applicable implementation
plan which have been delayed beyond the scheduled date(s) until such
time as their implementation has been assured. If the measure has
been partially implemented and it can be demonstrated that it is
providing quantifiable emission reduction benefits, the emissions
analysis may include that emission reduction credit."
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If a control measure in an approved SIP is delayed or changed in whole
or in part (e.g., the legislative authority of a program has changed), then
conformity determinations must reflect such a delay or change including
situations in which a measure is cancelled or changed after the conformity
analysis begins. Section 93.122(a)(3) also requires that DOT'S conformity
determination be made only when regulatory control programs have been
assured and will be implemented as described in the SIP.
In addition, regional emissions analyses must be based on the latest
information available at the time the analysis begins regarding the
effectiveness of SIP programs that are being implemented. Section 93.110(e)
of the conformity rule states, "[t]he conformity determination must use the
latest existing information regarding the effectiveness of TCMs and other
implementation plan measures which have already been implemented." See
EPA's July 1, 2004, final rule for further information on 40 CFR 93.110 and
93.122 requirements (69 FR 40054-40055).
The interagency consultation process should be used to determine the latest
planning assumptions regarding implementation of approved SIP measures. It is critical
that all parties understand the impacts of altering the implementation of approved SIP
measures. State and local air agencies or other agencies that are responsible for air
quality planning should inform transportation planners and provide technical assistance
in quantifying the impact when the implementation of approved SIP measures could
alter the emission reduction benefits assumed in previous conformity determinations. In
addition, state and local air agencies should consider how SIP implementation issues
can be addressed. They should immediately discuss how to make up for the emissions
shortfalls and remedy the SIP, possibly through addressing implementation delays. The
interagency consultation process should also be used to consider whether delays in the
SIP's control measures necessitate a SIP revision to incorporate other measures. EPA
commits to share information through the interagency consultation process as
appropriate when the implementation of an approved SIP measure changes and to
address the implementation issues through the SIP process.
Local, state, and federal agencies are also encouraged to be proactive in
considering the impacts on the conformity process before the implementation of an
approved SIP measure is changed. It is generally expected that air quality agencies
would assist transportation agencies in quantifying the impacts of a change in approved
SIP measures. The details of how this is accomplished should be determined through
the interagency consultation process.
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2.11 Can an area that does conformity for several different pollutants rely on different
planning assumptions in its conformity determination?
Planning assumptions that are applicable to conformity determinations for
different pollutants must be consistent (40 CFR 93.110)). For example, local estimates
of population, employment, travel, and congestion must be consistent among analyses
for different pollutants and precursors. Of course, there may be assumptions that would
vary due to the inherent differences in analyzing pollutants (e.g., temperatures may be
different for ozone and CO analyses due to the seasons in which these pollutants are
formed). Where there are differences in planning assumptions for different pollutants,
these differences should be explained in the documentation for the conformity
determination.
2.12 Does a revision in latest planning assumptions trigger a new conformity
determination?
No. A new regional emissions analysis and conformity determination would not
be required solely to incorporate revised planning assumptions (40 CFR 93.122(g)).
Although revisions to planning assumptions would not trigger a conformity
determination, future conformity determinations and supporting analyses must include
the revised assumptions (40 CFR 93.110(a)).
2.13 Can an MPO rely on a previous regional emissions analysis even if planning
assumptions have changed?
Yes. MPOs can rely on a previous emissions analysis if the requirements for 40
CFR 93.122(g) are met (e.g., no regionally significant projects have changed, no more
than four years have elapsed since the last regional emissions analysis). An MPO can
rely on the previous analysis when no new transportation or emissions modeling is
otherwise required (e.g., when a TIP is updated and the transportation plan has not
changed) (58 FR 3778). Conformity determinations that rely on a previous analysis do
not restart the four-year conformity requirement (40 CFR 93.122(g)(3) and 69 FR
40060).5
5 It is important to note that the conformity rule requires a new transportation plan and TIP conformity
determination and regional emissions analysis at least every four years (40 CFR 93.104(b)(3) and (c)(3)).
These determinations are done in many areas when the transportation plan is updated. The regional
emissions analysis must be based on a new planning horizon of at least 20 years and the latest planning
assumptions.
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2.14 How do the latest planning assumption requirements apply to project-level
conformity determinations and hot-spot analyses?
In general, section 93.109(b) of the conformity rule requires project-level
conformity determinations to meet the latest planning assumptions requirements, but
there are some additional requirements and considerations that also need to be taken
into account when a hot-spot analysis is required. Hot-spot analysis assumptions for
individual projects must be consistent with those assumptions used in the regional
emissions analysis for those inputs which are required for both analyses (40 CFR
93.123(c)(3)). However, a future transportation plan and TIP update and conformity
determination which incorporates revised planning assumptions in the regional
emissions analysis would not trigger a new hot-spot analysis for a project included in
the prior transportation plan and TIP unless there has been a significant change in the
project's design concept and scope; three years elapse since the most recent major
step to advance the project; or initiation of a supplemental environmental document for
air quality purposes. See section 40 CFR 93.104(d) of the conformity rule for more
details. The interagency consultation process must be used to determine what planning
assumptions are appropriate for hot-spot analyses (40 CFR 93.105(c)(1)(i)).
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Section 3: Implementation of the Latest Planning Assumption Requirements
3.1 How should state and local agencies define the "time the conformity analysis
begins"?
As described previously, the conformity rule requires conformity determinations
to be based on the latest planning assumptions available at the time the conformity
analysis begins. Section 93.110(a) of the conformity rule states, "[t]he 'time the
conformity analysis begins' is the point at which the MPO or other designated agency
begins to model the impact of the proposed transportation plan or TIP on travel and/or
emissions." Any information and assumptions that become available before actual
modeling for a conformity determination has commenced would be required to be
considered in that conformity determination (69 FR 40053). In addition, section
93.110(a) of the conformity rule requires that "New data that becomes available after an
analysis begins is required to be used in the conformity determination only if a
significant delay in the analysis has occurred, as determined through interagency
consultation."
Section 93.105(c)(1)(i) requires the interagency consultation process to be used
to decide which planning assumptions and models are available for use by the MPO or
other designated agencies responsible for conducting conformity analyses. This point
should be defined through interagency consultation and used consistently for all future
conformity determinations. EPA encourages the MPO or other designated agency to
use the interagency consultation process to inform other involved agencies of when a
conformity analysis has started for a given conformity determination. The interagency
consultation process would also be used to determine whether a significant delay has
occurred and whether new data that becomes available during a delay should be
incorporated.
The preamble to the July 1, 2004, final rule (69 FR 40053) provides several
examples for when the conformity analysis begins including:
• The point at which travel demand modeling begins to generate the VMT and
speed data that will be used to calculate emissions estimates for the conformity
determination.
• For smaller MPOs and rural areas that do not use a travel demand model the
point at which VMT projections necessary to run the emissions model are
calculated based on the most recent HPMS, population and employment data
that are available at that time.
The preamble to the July 1, 2004, final rule also provides several examples for
when the conformity analysis does not begin including:
• When the initial list of projects for the plan and TIP have been developed or
before those projects have been coded into the transportation network;
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• If travel or emissions modeling is conducted to preliminarily examine the impact
of several potential projects or project alternatives on travel or emissions in the
area; or,
• When an initial schedule for completing an analysis is developed during an
interagency consultation meeting.
3.2 To support a valid conformity determination, what planning assumption
information should be documented?
When an MPO or other designated agency conducts a conformity determination,
it should document in its determination the "time the conformity analysis begins" as
determined by interagency consultation, the date on which the analysis was started, and
the planning assumptions that were used.
To support a valid conformity determination, the MPO or other appropriate
agency should document the following specific information:
• How the "time the conformity analysis begins" has been defined through
interagency consultation;
• The calendar date that the conformity analysis began; and,
• The planning assumptions used in the conformity analysis.
Documenting this information in the actual conformity determination informs the
public of decisions regarding the use of latest planning assumptions, and will record
when an analysis has begun, so that commenters can address any issues related to
these decisions (40 CFR 93.105(e)). See the July 1, 2004 final rule preamble for more
information (69 FR 40054).
3.3 If new data becomes available after the analysis begins, should it be included in
the conformity determination?
New data (e.g., population or fleet data) that becomes available after the
conformity analysis begins is not required to be incorporated into the current analysis if
the analysis is on schedule, although an area could voluntarily include the new
information at any time, as appropriate. Section 93.110(a) of the conformity rule
requires that new data that becomes available after an analysis begins be used in the
conformity determination only if a significant delay in the analysis has occurred, as
determined through interagency consultation. An example of a significant delay in the
conformity analysis would include the case where an MPO starts a conformity analysis
and begins generating VMT estimates from the travel demand model and the MPO's
analysis is then delayed for six months (69 FR 40054). In such cases where a
significant delay occurs, EPA believes that it is reasonable to expect that the MPO must
incorporate new planning information that became available during the six-month delay
period (40 CFR 93.110(a)).
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In cases when there has not been a significant delay in the analysis, interagency
consultation parties have discretion to decide if data available after the analysis begins
should be incorporated, and should base this decision on whether substantial work has
been completed. Although including new data that becomes available after the analysis
begins is not automatically required, EPA and DOT encourage agencies to include such
data if the schedule of the conformity determination can accommodate it.
3.4 Must an area wait to start the conformity analysis until anticipated changes in
planning data become available?
The Clean Air Act and transportation conformity rule do not require state and
local planners to delay their conformity analyses to incorporate anticipated data that is
not yet available for conformity purposes (69 FR 40056). Section 93.110(a) requires
conformity determinations to incorporate the only most recent planning information
available at the time the conformity analysis begins although the consultation process
should not be used to unduly delay or exclude the use of new information or to
selectively employ it for the convenience of the conformity process.
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