PM10 SIP as a localized concern.
    Today's final rule does not require any hot-spot analysis--
qualitative or quantitative--for all other projects that are not listed
in Sec.  93.123(b)(1) as an air quality concern. These projects are
presumed to meet Clean Air Act requirements and 40 CFR 93.116

without any explicit hot-spot analysis, because EPA concludes based
upon the available evidence that such projects would not have an impact
on local air quality. State and local project sponsors should briefly
document in their conformity documentation for such projects that an
explicit PM10 hot-spot analysis was not completed because
Clean Air Act and 40 CFR 93.116 requirements were met without an
explicit PM10 hot-spot analysis.
    This final rule requires PM10 hot-spot analyses for
projects of air quality concern in PM10 nonattainment and
maintenance areas at all times--both before and after a PM10
SIP is submitted. These projects are anticipated to have the potential
to increase local PM10 concentrations, and as a result,
PM10 hot-spot analyses are needed to ensure that the local
air quality impacts of such projects are considered prior to receiving
federal funding or approval. Rather than finalize the proposed and
previous rule's criteria for PM10 analyses, EPA is
finalizing more specific criteria about the types of projects that
require such analyses based on our November 2003 and December 2004
proposals and comments received. See Section V. of this notice for
further details regarding the regulatory criteria for projects of air
quality concern and more information on the general requirements for
performing hot-spot analyses. See Section IX. of today's action for
further information regarding when today's change in PM10
requirements would apply in PM10 areas with and without
approved conformity SIPs.
    In addition, the final rule does not substantively change the
existing conformity rule flexibility that allows DOT, in consultation
with EPA, to make categorical hot-spot findings that would further
streamline quantitative hot-spot analysis requirements in appropriate
cases, as described further in Section VII.
    This final rule also makes no change in how qualitative
PM10 hot-spot analyses are currently performed for projects
of air quality concern, since the previous conformity rule has always
required a qualitative PM10 hot-spot analysis for all non-
exempt projects in PM10 nonattainment and maintenance areas
(under the previous rule's Sec.  93.123(b)(2)). As stated in Section
III., quantitative PM10 hot-spot analyses are not required
for projects of air quality concern at this time since EPA has not yet
required quantitative PM10 hot-spot analyses under Sec.
93.123(b)(4). Qualitative PM10 hot-spot analyses should be
completed according to joint EPA and DOT guidance, which will be posted
on the Web site provided in Section I.B.2. of today's notice. Until
this new guidance is available, FHWA's existing September 12, 2001
guidance, ``Guidance for Qualitative Project-Level `Hot-Spot' Analysis
in PM10 Nonattainment and Maintenance Areas,'' can be used.
See Section VI. of this final rule for more information regarding the
timing of EPA's future quantitative hot-spot modeling guidance and
application of quantitative requirements.
    Finally, EPA notes that its future quantitative modeling guidance
will address how the current 24-hour and annual PM10 air
quality standards are to be considered in quantitative hot-spot
analyses. This future guidance will be consistent with how potential
impacts on the PM10 standards have historically been
considered for SIP planning, monitoring, and other applicable
requirements.

C. Rationale

    EPA considered the following factors in developing the final rule's
PM10 hot-spot requirements:
     The Clean Air Act conformity requirements for individual
transportation projects in PM10 areas;
     The current scientific understanding of PM10
hot-spots and public health effects;
     The feasibility of implementing proposed options; and
     The impact of proposed options on state and local
resources.
    EPA stated in its proposals that it was important to re-evaluate
the need for hot-spot analyses for PM10 nonattainment and
maintenance areas, in conjunction with similar options considered for
PM2.5 hot-spot requirements. The following paragraphs
outline how EPA considered the above factors in the final rule.
    When the conformity rule was promulgated in 1993, EPA interpreted
Clean Air Act section 176(c)(1)(B) to require PM10 hot-spot
analyses because of the requirement to ensure that transportation
activities do not create new violations, worsen existing violations or
delay timely attainment of the air quality standard (January 11, 1993,
58 FR 3776-3777). EPA continues to believe that this statutory
provision is the applicable standard that applies for considering a
final PM10 hot-spot requirement, and that the final rule
meets this legal standard.
    Furthermore, the Clean Air Act requires that section 176(c)(1)(B)
be met for all FHWA or FTA funded or approved projects, except for
traffic signal synchronization projects; it does not distinguish that
these requirements apply based on whether or not a SIP has been
submitted. Through previous rulemaking, EPA has determined that the
exempt projects listed in 40 CFR 93.126 have met section 176(c)(1)(B)
without further hot-spot analyses. Through today's action, EPA is
determining that projects not identified in the rule as projects of air
quality concern have also met section 176(c)(1)(B) without further hot-
spot analyses. The final rule requires that all projects of air quality
concern be analyzed for localized impacts, regardless of whether or not
the PM10 SIP is submitted.
    As indicated in Section III. of today's notice and above, EPA
believes that Clean Air Act section 176(c)(1)(B) is the primary legal
standard that applies for this final rule. This statutory provision
requires that federally funded and approved projects not create or
worsen air quality violations or delay timely attainment. Also, since
projects of air quality concern have the potential to impact local
PM10 air quality, then a PM10 hot-spot
requirement is warranted for such projects in today's final rule at all
times.
    EPA also continues to believe it has discretion to establish the
level of PM10 hot-spot analysis that is necessary to meet
statutory requirements. Therefore, EPA is retaining its previous rule's
approach for requiring quantitative PM10 hot-spot analyses
only for projects of air quality concern once EPA's modeling guidance
is available. EPA is revising some of the existing rule's criteria for
when PM10 analyses are required based on scientific
information currently available on PM10 hot-spots, and the
Agency's experience in implementing CO and PM10 hot-spot
requirements since 1993 for what level of analysis is appropriate and
worthwhile. The final rule's criteria for what projects require hot-
spot analyses will ensure that all projects that have the potential to
impact the air quality standards will be analyzed before they receive
Federal funding or approval. EPA revised its proposed and previous
rule's criteria for what projects of air quality concern require
PM10 analyses based on existing scientific information and
comments received, as discussed further in this section and in Section
V.
    Furthermore, as stated in Section III., EPA is changing its
precedent to date in no longer requiring qualitative hot-spot analyses
for projects that are not of localized air quality concern. As stated
previously, since the original 1993 conformity rule, some type of hot-
spot analysis has been required to meet statutory requirements for all
non-exempt FHWA and FTA projects in

PM10 nonattainment and maintenance areas. However, based on
the history of implementation of this provision to date, EPA now
believes that these projects do not represent a localized air quality
concern and can be presumed to meet Clean Air Act requirements and 40
CFR 93.116 without any explicit hot-spot analysis because EPA concludes
based on available data and experience that these projects will not
have an impact on local air quality.
    The Agency now believes that requiring qualitative hot-spot
analyses for projects that are not a concern is also not a beneficial
use of Federal, state, or local resources. This conclusion is based in
part on a recent review by EPA and DOT field offices of project-level
conformity determinations involving historical qualitative hot-spot
analyses in PM10 areas. See Section III.C. for further
information on EPA and DOT's review of PM10 qualitative hot-
spot analyses and why EPA concludes that they are no longer necessary
to meet statutory requirements for projects that are not an air quality
concern.
    However, EPA continues to believe that projects of air quality
concern have the potential to impact PM10 air quality
standards and thus require explicit hot-spot analyses to determine if
any such impacts will result in specific cases, based on existing
scientific information and the Agency's historical understanding of
PM10 hot-spots. As stated in the December 2004 supplemental
proposal, EPA continues to believe it is appropriate to focus
conformity resources where air quality issues are significant and thus
need to be in place to address Clean Air Act requirements.
    In developing this final rule, EPA considered information that was
available when the original 1993 conformity rule was developed, as well
as new information that was submitted through the rulemaking process or
has otherwise become available. For example, in 1993, EPA stated that
direct PM10 emissions would be capable of causing violations
in conditions of unusually heavy diesel truck/bus traffic and limited
dispersion, such as street canyons (January 11, 1993, 58 FR 3780). EPA
has also acknowledged that the role of re-entrained road dust could be
a major factor in contributing to potential PM10 hot-spots,
especially in PM10 areas where road dust is a major
component of the PM10 motor vehicle emissions inventory.
    EPA also considered in the final rule the impact of our new diesel
fuel and engine standards (January 18, 2001, 66 FR 5002) for the
necessity of applying any PM10 hot-spot requirement. Such
standards are expected to significantly impact the amount of
particulate emissions that will be emitted by new diesel vehicles, and
consequently may impact the potential for PM10
transportation-related hot-spots. We considered the time frame over
which these vehicle standards would phase in. According to the latest
Vehicle Inventory and Use Survey from the Census Bureau, in 2002,
vehicles three years of age and younger constituted only 32.3% of U.S.
truck fleet. If the same age distribution holds for 2010, only about
one third of trucks on the road will meet the heavy-duty engine
emissions standards for 2007 and 2010. In this scenario, most trucks on
the road will still be capable of producing elevated concentrations. As
such, EPA's new emission standards do not eliminate the need for
considering PM10 hot-spots from transportation projects
involving a significant number of diesel vehicles. However,
consideration of EPA's diesel fuel and engine standards' impact on
background air quality will be addressed as part of EPA's future
quantitative modeling guidance and possibly in modeling used to support
categorical hot-spot findings as described in Section VII. of today's
notice.
    As described further below, EPA also considered the feasibility and
resource implications of implementing the proposed options and the
final rule's requirements to meet statutory requirements before and
after PM10 SIP submission.

D. Response to Comments

    EPA received comments from state and local transportation and air
quality agencies, environmental groups, transportation advocates, and
the general public with respect to the proposed options for
PM10 areas. Fewer comments were submitted for
PM10 options as compared to PM2.5 options, and
preferences were not as consistent for similar options before and after
PM10 SIPs are submitted, as compared to preferences for
PM2.5 options.
Comment
    Several commenters supported finalizing PM10
requirements that were generally consistent with the previous
conformity rule's provisions for PM10 areas (i.e., Options 1
and A) because they believed these options were most protective of
public health. Commenters also supported these options because they
would promote consistency with EPA's past legal interpretations
regarding how federally funded and approved transportation projects
have historically met Clean Air Act section 176(c)(1)(B) requirements
in PM10 areas. These commenters believed that existing
science and experience have shown that transportation projects can
impact local PM10 air quality, and therefore, previous
PM10 hot-spot requirements should be retained to meet
statutory requirements.
    These commenters generally did not support Options 4 and C since
they required no PM10 hot-spot analyses, and they believed
that these options were inconsistent with current scientific evidence
regarding the existence of PM10 hot-spots. A few commenters
indicated that these options also do not provide the same health
protections as other options. Similarly, another commenter stated that
it was not in the public's best interest to eliminate all analyses of
potential PM10 hot-spots, especially due to the commenter's
experience with respect to the 24-hour PM10 standard.
Another commenter argued that hot-spot requirements should not be
deleted because of the known relationship between PM10
nonattainment areas and transportation-related sources.
    Some of these commenters acknowledged that in practice, proposed
options prior to a PM10 SIP's submission would not impact
most areas, but believed if any projects are approved for areas that
have yet to submit a PM10 SIP, those projects can only meet
statutory conformity requirements through a PM10 hot-spot
analysis. One commenter believed that PM10 areas that still
do not have SIPs need to complete PM10 hot-spot analyses
because these SIPs are not reliable in protecting the public health of
their citizens. Another commenter argued that consistency with existing
PM10 hot-spot requirements and procedures for conformity
provides better support during environmental reviews from a NEPA and/or
state environmental process perspective when determining local or
project-level impacts.
    Still other commenters supported options that would apply no
PM10 hot-spot requirements (i.e., Options 4 and C), and some
even preferred that EPA delay issuing a final rule until certain issues
are addressed. Some of these commenters believed that there was
insufficient evidence regarding the existence of PM10 hot-
spots. Some commenters also argued that PM10 hot-spot
requirements are not required by the Clean Air Act, and therefore, an
option that required PM10 hot-spot analyses should never be
finalized.
    These commenters were also opposed to requiring existing
PM10 hot-spot requirements (under Options 1 and A) because
they believed these options

would require extensive analyses without comparable environmental
benefits and flexibility. These commenters believed it was unnecessary
to require hot-spot analyses for every project in every PM10
area.
    One of these commenters stated that they had never identified a
transportation project that had a negative impact on PM10
concentrations. This commenter noted that transportation projects
usually reduce PM10 emissions because most projects involve
paving unpaved roads and/or shoulders or adding curbs or gutters. The
commenter noted that in most mountainous western states,
transportation-related PM10 problems result from highway
maintenance combined with winter air inversions rather than highway
improvement projects. This commenter stated that these problems are
addressed in the SIP through requirements for street sweeping, flushing
and use of chemical de-icers, all of which reduce road dust. Finally
the commenter indicated that eliminating PM10 hot-spot
requirements is preferable because state and local agencies can then
focus their limited resources on other transportation and air quality
efforts.
Response
    As described above, EPA believes that today's final rule is the
appropriate way for projects of air quality concern to meet Clean Air
Act section 176(c)(1)(B) requirements in all PM10
nonattainment and maintenance areas. EPA agrees that applying a hot-
spot requirement prior to a PM10 SIP being submitted is
essential for meeting statutory requirements. EPA agrees that today's
final rule is consistent with its past legal interpretations for
applying hot-spot requirements for all projects of air quality concern.
    EPA disagrees with commenters who argued that there is insufficient
information or limited value in applying a PM10 hot-spot
requirement. Although some commenters noted limited value in performing
qualitative PM10 hot-spot analyses to date, EPA believes
that this information further supports its decision to eliminate
qualitative PM10 hot-spot analyses for projects that are not
an air quality concern, rather than eliminate all PM10 hot-
spot requirements.
    Based on our review of scientific studies and information gathered
during the rulemaking process, as described above, EPA believes that
projects of air quality concern have the potential to impact
PM10 concentrations, and as a result, the PM10
standards. Such impacts on communities surrounding a project would be
contrary to the Clean Air Act's conformity requirements. Thus, EPA
concludes that hot-spot analyses are necessary for projects of air
quality concern. Furthermore, EPA does not agree that it is appropriate
to delay finalizing a change to the PM10 hot-spot
requirements, for the reasons cited above. EPA has addressed state and
local resource concerns by eliminating PM10 qualitative hot-
spot analyses for projects that are not an air quality concern.
Comment
    EPA also proposed Option B that relied solely on the SIP to
identify projects or project locations of potential PM10
hot-spot concern. Under this option, quantitative PM10 hot-
spot analyses would only be required at types of project locations
identified as a localized air quality concern in a given
PM10 SIP. No quantitative or qualitative analyses would be
required for projects in other types of locations, or in
PM10 areas where the current or future SIP does not identify
types of locations as a localized PM10 air quality concern.
Furthermore, no hot-spot analyses would be completed for any projects
prior to PM10 SIP submission, for the limited number of
PM10 areas without SIPs.
    Several commenters supported Option B because they believed that
the SIP process could assist in identifying what projects are of
concern in a given area and what level of PM10 hot-spot
analysis is appropriate. Commenters believed that Option B would allow
each PM10 area to target potential PM10 hot-
spots, protect public health, and provide necessary flexibility. A few
other commenters indicated support for Option B because they did not
agree that there was evidence that transportation projects are a
PM10 hot-spot concern. Two other commenters even believed
that this option should apply only once a SIP is approved, rather than
when a SIP is submitted, unless EPA were establishing a process similar
to its adequacy process for submitted SIPs with motor vehicle emissions
budgets that involves sufficient notice and public review.
    Other commenters opposed Option B because they believed it was not
feasible, and therefore, would not meet statutory requirements or
protect public health. Commenters noted that most PM10 areas
already have SIPs that were developed before EPA's proposed options,
without consideration for implementing a conformity hot-spot
requirement. If finalized, the commenters believed that Option B would
result in new projects in most PM10 areas not meeting
statutory requirements, since no hot-spot requirement would exist
(because no current PM10 SIPs were designed to implement
such a requirement).
    Some commenters believed that Option B is also flawed because a
state has no obligation under the Clean Air Act or conformity
regulations to identify project locations of air quality concern in its
SIP. Commenters argued that if states decline to designate such areas
in their SIPs--whether from the lack of meaningful evidence of problems
or out of a desire to avoid the application of conformity
requirements--statutory requirements would not be met. If such a case
occurred, this commenter was concerned that there would be no legal
mechanism to challenge a SIP or enforce statutory conformity
requirements.
    A commenter who did not support Option B as proposed suggested a
hybrid option where PM10 areas could rely on Option B if the
SIP addressed the potential for transportation-related hot-spots, but
if this was not the case, the existing PM10 requirements
under Option A would apply.
    Some commenters also provided information and thoughts on
developing PM10 SIPs to implement Option B. One commenter
believed that revising existing SIPs to address transportation-related
PM10 hot-spots would allow state and local agencies to focus
their resources on meaningful analyses. Some commenters believed that
available local information and resources to develop SIPs to specify
project locations of concern will vary among PM10 areas.
Still another commenter was concerned that Option B could be
problematic if project locations are not identified during SIP
development, but are subsequently determined through the consultation
process to have a hot-spot concern. Other commenters believed that the
consultation process could be used to identify new projects of concern,
rather than revise existing SIPs.
    Finally, a few commenters went on to state that EPA's proposed
options that allow states to determine which projects would require
hot-spot analyses conflict with a previous court decision. However, the
commenters did not elaborate on what court decision was involved, or
how Option B contradicted this judicial decision.
Response
    EPA is not finalizing Option B because this option will not ensure
that all federally funded and approved transportation projects in
PM10 areas are consistent with Clean Air Act section
176(c)(1)(B). As described by

commenters, most PM10 areas already have SIPs that were
established prior to EPA's proposed conformity options, and therefore,
were not designed to implement Option B. Due to limited resources, it
is doubtful that areas will revise SIPs solely to address
PM10 hot-spots, and even so, it is unclear whether SIPs
could be developed with sufficient detail to consider the local impacts
of current and future projects. Based on all of these considerations
and the comments received, EPA does not believe that it is realistic or
practical to expect that Option B can be sufficiently implemented to
meet statutory requirements in all PM10 areas. Further
discussion on a similar option for PM2.5 hot-spot analyses
can be found in Section III. of today's action.
Comment
    A few commenters supported Options 2 or 3 which would apply
existing PM10 hot-spot requirements depending on whether or
not new or worsened local PM10 violations could occur in a
given area prior to PM10 SIP submission. For example, one
commenter believed Option 3--which would require PM10 hot-
spot analyses if EPA or the state air agency found there to be a hot-
spot concern in a given area--would provide the ability to require
analyses for certain projects. This commenter highlighted his area's
experience that two types of projects listed in 40 CFR 93.126 (i.e.,
weight inspection stations and bus terminals) may be a PM10
hot-spot concern due to a high concentration of diesel vehicles.
Response
    EPA is not finalizing approaches such as Options 2 or 3 because it
is unclear if they can be implemented in a manner that meets statutory
requirements. See Section III. of today's action for further rationale
regarding why such options are not being finalized. However, today's
final rule provides some of the flexibility intended by these options,
i.e., targeting PM10 hot-spot analyses for projects that
have the potential to impact PM10 air quality.
Comment
    A few commenters argued that EPA may not lawfully finalize options
that defer PM10 hot-spot analyses until after a SIP is
submitted because such delays are inconsistent with Clean Air Act
requirements. Commenters believed that Clean Air Act section 176(c)(1)
does not require that a SIP for a given standard be established before
conformity requirements for that standard apply. Section 176(c)(1)
states that Federal and MPO approval actions cannot be done for ``* * *
any project * * * which does not conform to an implementation plan
approved or promulgated under section 7410 of this title.''
Response
    EPA agrees that it is not appropriate to defer project-level hot-
spot analyses until PM10 SIPs are developed, and thus has
not chosen these proposed options in the final rule. See Section III.
for more on EPA's response to a similar comment raised for
PM2.5 hot-spot analyses.
Comment
    Some commenters were concerned that finalizing options that
required PM10 hot-spot analyses for all projects (Options 1
and A) could result in an inefficient use of state and local resources,
and therefore, deleting or defining PM10 hot-spot
requirements through the SIP process was a more appropriate use of
resources.
    However, as stated above, other commenters believed that having no
or only limited PM10 hot-spot analyses did not meet
statutory requirements or protect public health. Furthermore, they
believed that implementing the previous PM10 hot-spot
requirements has not been burdensome, so continuing to do this under
the final rule would be acceptable.
Response
    EPA believes that the final rule will ensure that state and local
resources are used in an efficient manner, since PM10 hot-
spot analyses will only be required for projects of air quality
concern. Eliminating qualitative PM10 hot-spot analyses for
projects that are not an air quality concern will significantly reduce
any resource challenges in implementing this final rule, since most
projects should not be considered an air quality concern. As noted
above, EPA concludes that this does comply with statutory requirements.
EPA will continue to work with DOT to assist state and local agencies
in implementing the final rule's requirements.
Comment
    Other commenters were concerned that EPA has yet to issue
PM10 quantitative hot-spot analysis guidance and methods.
Some commenters supported doing little or no PM10 hot-spot
analyses, in part because credible tools are not currently available.
However, other commenters believed that all of the proposed options
were insufficient since they would delay quantitative PM10
hot-spot analyses for years, and in the interim, there would be no
consideration of the public health impacts of projects currently under
development.
Response
    Today's final rule retains Sec.  93.123(b)(4) of the existing
conformity rule that requires quantitative PM10 hot-spot
analyses once EPA announces in the Federal Register that quantitative
analysis requirements are in effect. EPA has not yet made such an
announcement because the Agency believes that appropriate motor vehicle
emissions factor models are not yet available for localized analyses,
and EPA is in the initial stages of developing quantitative hot-spot
modeling guidance to implement today's rule. Please see Section VI. of
today's final rule for further information on the timing of
quantitative hot-spot requirements. However, pending development of
such guidance, the final rule does require qualitative PM10
hot-spot analyses for all projects of air quality concern, so
consideration of the public health impacts of proposed projects of air
quality concern will not be delayed.
Comment
    Some commenters stated that PM10 hot-spot requirements
should be suspended until (1) it can be demonstrated scientifically
that re-entrained dust from induced traffic creates PM10
hot-spots, and (2) there are more reliable techniques to quantify re-
entrained PM10 created by induced traffic on paved roads.
    Another commenter stated that it is reasonable to expect that some
projects would create localized impacts, especially due to the large
amounts of re-entrained road dust generated from roadways. This
commenter believed that EPA should develop criteria and guidance under
which EPA, state or local air pollution control agencies would have the
option of requiring project-level PM10 hot-spot analyses.
Another commenter went on to state that, while re-entrained road dust
emissions can be a greater contributor to PM10
concentrations than tailpipe emissions, most projects are done on paved
roads where re-entrained road dust is less of an issue compared to
unpaved roads.
Response
    EPA believes based on the available evidence included in the docket
for this rulemaking that certain transportation projects have the
potential to impact PM10 air quality standards, and
therefore, a PM10 hot-spot analysis for these projects is
needed to meet statutory requirements. Furthermore,

sufficient scientific information exists to support the final rule's
requirements, and EPA will consider whether additional information is
warranted for modeling road dust in its future PM2.5 and
PM10 quantitative hot-spot modeling guidance.
Comment
    Some commenters believed that EPA could improve on its proposed
options in the final rule, such as adopting a screening method or
emissions threshold that would help define what projects require
quantitative hot-spot analyses.
Response
    EPA believes that today's action addresses this comment by further
refining what projects are an air quality concern and need
PM10 hot-spot analyses. See Section V. for further
information on the criteria for projects of air quality concern
finalized in today's action. The elimination of qualitative hot-spot
analyses for projects not of concern in part addresses the motivation
for a screening method or emissions threshold--e.g., to focus more
rigorous quantitative analyses on projects of air quality concern.
Comment
    A few commenters argued that applying the previous PM10
hot-spot requirements was not necessary due to unique circumstances of
their individual PM10 area. Several commenters stated that
it is inefficient to direct resources to PM10 hot-spot
analysis when transportation projects may not be a significant
contributor to the PM10 problem in a given area, such as
smaller areas or cities dominated by other PM sources.
    One commenter said there were four PM10 nonattainment
and maintenance areas in their state where the operation of specific
industries (e.g., quarries, cement plants, steel fabrication plants) is
the primary source of direct PM10 emissions. Monitors over
the last ten years have shown attainment for the PM10
standards, but the commenter's state had not submitted redesignation
requests to maintenance for two of the areas due to local concerns for
specific non-transportation sources. Therefore, this commenter
supported the option of only requiring PM10 hot-spot
requirements if a SIP is submitted that identifies transportation
sources as a significant contributor to the PM10 air quality
problem.
    Another commenter believed its state needed flexibility to
consider, through the SIP and consultation processes, the hot-spot
concerns of its remote communities. The commenter believed the existing
PM10 hot-spot requirements resulted in a one-size-fits-all
approach that is not appropriate for its PM10 nonattainment
and maintenance areas.
Response
    EPA believes that the final rule's PM10 hot-spot
requirements along with the conformity rule's existing provisions
concerning areas with insignificant emissions serve to protect air
quality and public health in PM10 nonattainment and
maintenance areas. First, today's final hot-spot rule targets
PM10 hot-spot analyses only for projects that are likely to
cause or contribute to new or worsened PM10 violations.
Specifically, the rule targets hot-spot analyses on those types of
projects that result in significant increases in diesel vehicle traffic
and emissions, which is likely to be a small subset of projects in many
areas.
    Second, 40 CFR 93.109(k) already allows PM10 areas with
insignificant regional motor vehicle emissions to demonstrate, when
appropriate, that individual projects will not create new localized
violations or make existing violations worse. Projects in such cases
would not require PM10 hot-spot analyses. Therefore, areas
where other types of sources principally contribute to nonattainment
problems (such as specific stationary sources) would only be required
to perform PM10 hot-spot analyses for the types of projects
described in Sec.  93.123(b)(1) until such time as a SIP is submitted
which demonstrates that regional PM10 on-road emissions are
insignificant and that projects will not cause new violations or make
existing violations worse.
    EPA also acknowledges that the practical impact of today's final
rule may have a minimal impact on the small areas described by
commenters, since there may not be a large number or any projects of
air quality concern developed before a PM10 SIP is submitted
that demonstrates insignificance. After EPA makes an adequacy finding
on (or approves) such a SIP, PM10 hot-spot analyses would no
longer be required in that area. EPA Regions and states can work
together to expedite the processing of such SIPs through such methods
as parallel processing or direct final rulemaking as appropriate.
    With regard to the concerns expressed about the appropriateness of
hot-spot analyses in remote or non-urbanized areas, EPA would like to
point out that today's final rule limits the need for PM10
hot-spot analyses to only those projects which significantly increase
diesel vehicle traffic and emissions. As noted in Section III., this is
likely to be only a small percentage of projects in remote or non-
urbanized areas.
Comment
    A few commenters argued that EPA's standards for low sulfur diesel
fuels in 2006 and heavy-duty engines in 2007 will negate any need for
PM10 hot-spot analyses. The commenters stated that EPA
should analyze the impacts of these federal standards on local air
quality before the rule is finalized.
Response
    As described in C. of this section, EPA has considered the impacts
of the new diesel standards, and has determined that PM10
hot-spot analyses are still warranted for projects of air quality
concern. However, consideration of EPA's diesel fuel and engine
standards' impact on background air quality will be addressed as part
of EPA's future quantitative modeling guidance and possibly in modeling
used to support categorical hot-spot findings as described in Section
VII. of today's notice.
Comment
    One commenter expressed support for the previous conformity rule's
PM10 hot-spot requirements until the current PM10
standards are replaced by a new PM-coarse air quality standard, because
current hot-spot requirements protect public health.
Response
    EPA will evaluate the impact of any new air quality standards and
how they impact the current PM10 transportation conformity
requirements, including hot-spot requirements, if and when such
standards are promulgated. However, since the PM10 standards
and applicable requirements continue to apply at this time, today's
final rule continues to address the current PM10 standards.
As explained above, EPA has concluded that requiring hot-spot analyses
only for projects of air quality concern provides for both compliance
with statutory requirements and appropriate commitment of resources.

E. Responses to Other Comments

    EPA received several comments on PM2.5 and
PM10 hot-spot analyses that covered broader legal arguments
or other topics than the proposed options. Rather than restate all of
those comments and responses again here, please see Section III.E. for
further information and response to these comments covering both
PM2.5 and PM10.

F. When Are the PM10 Hot-spot Requirements Effective?

    For reasons described in Section III.F., the final rule is
effective on April 5, 2006. Since the same provisions of the amended
rule apply in PM10 areas as well as PM2.5 areas,
EPA finds good cause to have these rules effective on April 5, 2006,
for PM10 areas as well. EPA believes it would not be in the
public interest to attempt to draft the regulations to apply to
different areas on different dates as it would be overly confusing and
difficult to implement. In addition, this final rule is published
almost 30 days before April 5, 2006, so PM10 areas should
not have any difficulty complying with these regulations as of April 5,
2006. See Section IX. of today's notice for more information on when
the final rule's PM10 hot-spot provisions will apply in
PM10 nonattainment and maintenance areas with approved
conformity SIPs.

V. Projects of Air Quality Concern and General Requirements for
PM2.5 and PM10 Hot-spot Analyses

A. Background

    This section covers the specific types of projects that are
required to have PM2.5 and PM10 hot-spot
analyses. The following paragraphs describe what the conformity rule
has previously required in PM10 areas as well as what types
of projects were proposed to receive PM2.5 and
PM10 hot-spot analyses under the November 2003 and December
2004 proposals.
    As stated in Sections III. and IV., EPA proposed in the December
2004 notice a range of options for when quantitative or qualitative
PM2.5 or PM10 hot-spot analyses would be required
for the time periods before and after a SIP is submitted. As part of
some of those options, EPA proposed to require the following projects
to have PM2.5 and PM10 hot-spot analyses:
     Section 93.123(b)(1)(i): Projects which are located at
sites at which violations have been verified by monitoring data;
     Section 93.123(b)(1)(ii): Projects which are located at
sites which have vehicle and roadway emission and dispersion
characteristics that are essentially identical to those of sites with
verified violations (including sites near one at which a violation has
been monitored);
     Section 93.123(b)(1)(iii): New or expanded bus and rail
terminals and transfer points which significantly increase the number
of diesel vehicles congregating at a single location; and
     Section 93.123(b)(1)(iv): Projects in or affecting
locations, areas, or categories of sites which are identified in the
PM2.5 or PM10 applicable implementation plan or
implementation plan submission, as appropriate, as sites of violation
or possible violation.
    These proposed criteria were generally consistent with what the
conformity rule had required for quantitative hot-spot analyses once
tools and EPA modeling guidance are released, since the original 1993
conformity rule in PM10 areas, with a few exceptions.
    First, EPA proposed to clarify that quantitative analyses would be
required only for new or expanded bus and rail terminals and transfer
points that significantly increase the number of diesel vehicles
(rather than any increase of diesel vehicles). Second, EPA proposed to
add a new criterion--consistent with the current rule's CO quantitative
hot-spot requirements--to require PM2.5 or PM10
quantitative hot-spot analyses for those projects that the
PM2.5 or PM10 SIP identifies as a hot-spot
concern.
    In addition, in the context of options that would rely on the SIP
to identify all projects of air quality concern (e.g., Option B), EPA
provided the following examples of types of projects and locations that
could be identified in a SIP, and as a result, need PM2.5 or
PM10 quantitative hot-spot analyses:
     Highly congested intersections,
     Locations of highest traffic volumes,
     Large transit stations or freight terminals where a
Significant increase in diesel vehicle traffic and engine idling
occurs,
     Projects involving long or steep grades, or
     Monitors where the PM2.5 or PM10
standards has been exceeded or violated.
    EPA noted in its proposals that the locations listed above are
similar to the conformity rule's original requirements in Sec.
93.123(a)(1)(i)-(iv) and Sec.  93.123(b)(1)(i)-(iii) for projects that
required quantitative hot-spot analyses in CO and PM10
areas. EPA requested comment on the above examples and for any other
information regarding other types of projects and locations where
potential PM2.5 or PM10 hot-spots could occur in
a given area. See the November 5, 2003 proposal (68 FR 62712) and
December 13, 2004 supplemental proposal (69 FR 72144) for further
background information. EPA also noted that any combination of proposed
PM2.5 or PM10 hot-spot options could be included
in the final rule.

B. Projects of Air Quality Concern

1. Description of Final Rule
    This final rule requires PM2.5 and PM10 hot-
spot analyses only for projects that are considered to have the
potential to impact the air quality standards (i.e., ``projects of air
quality concern''). Section 93.123(b)(1) of today's final rule requires
PM2.5 and PM10 hot-spot analyses for the
following projects of air quality concern:
     Section 93.123(b)(1)(i): New or expanded highway projects
that have a significant number of or a significant increase in diesel
vehicles;
     Section 93.123(b)(1)(ii): Projects affecting intersections
that are at Level-of-Service \7\ D, E, or F with a significant number
of diesel vehicles, or those that will change to Level-of-Service D, E,
or F because of increased traffic volumes from a significant number of
diesel vehicles related to the project;
---------------------------------------------------------------------------

    \7\ Highway Capacity Manual 2000 states on pp. 10-4 through 10-5
that ``[t]he average travel speed for through vehicles along an
urban street is the determinant of the operating level of service
(LOS). The travel speed along a segment, section, or entire length
of an urban street is dependent on the running speed between
signalized intersections and the amount of control delay incurred at
signalized intersections.'' Level-of-service D, E, and F are
considered the most congested intersections for planning purposes.
---------------------------------------------------------------------------

     Section 93.123(b)(1)(iii): New bus and rail terminals, and
transfer points, that have a significant number of diesel vehicles
congregating at a single location;
     Section 93.123(b)(1)(iv): Expanded bus and rail terminals,
and expanded transfer points, which significantly increase the number
of diesel vehicles congregating at a single location; and
     Section 93.123(b)(1)(v): Projects in or affecting
locations, areas, or categories of sites which are identified in the
PM10 or PM2.5 applicable implementation plan or
implementation plan submission, as appropriate, as sites of violation
or possible violation.
    Quantitative hot-spot analyses are required for conformity
determinations of such projects in PM2.5 and PM10
areas once EPA provides guidance and announces that such analyses are
required under Sec.  93.123(b)(4). See Section VI. for more information
regarding the timing of quantitative hot-spot analyses for projects of
air quality concern and EPA's future modeling guidance.
    Prior to quantitative analyses being required, section 93.123(b)(2)
requires qualitative PM2.5 and PM10 hot-spot
analyses for projects of air quality concern. State and local agencies
should follow EPA and DOT's guidance document for completing
qualitative

PM2.5 and PM10 hot-spot analyses, which will be
posted on the EPA Web site that is listed in Section I.B.2. of today's
notice. Until this new guidance is available, FHWA's existing September
12, 2001 guidance, ``Guidance for Qualitative Project-Level ``Hot-
Spot'' Analysis in PM10 Nonattainment and Maintenance
Areas,'' can be used for PM10 hot-spot analyses.
2. Examples
    Some examples of projects of air quality concern that would be
covered by Sec.  93.123(b)(1)(i) and (ii) are:
     A project on a new highway or expressway that serves a
significant volume of diesel truck traffic, such as facilities with
greater than 125,000 annual average daily traffic (AADT) and 8% or more
\8\ of such AADT is diesel truck traffic;
---------------------------------------------------------------------------

    \8\ This percentage is the national average of truck vehicle
miles traveled (VMT) to total VMT, based on FHWA's Highway
Statistics publication which can be found at: http://www.fhwa.dot.gov/policy/ohim/hs04/index.htm.
 EPA's MOBILE6.2 motor

vehicle emissions model also uses 8% truck VMT as a national
default.
---------------------------------------------------------------------------

     New exit ramps and other highway facility improvements to
connect a highway or expressway to a major freight, bus, or intermodal
terminal;
     Expansion of an existing highway or other facility that
affects a congested intersection (operated at Level-of-Service D, E, or
F) that has a significant increase in the number of diesel trucks; and
     Similar highway projects that involve a significant
increase in the number of diesel transit busses and diesel trucks.
    EPA notes that the above examples are considered to be the most
likely projects that would require a PM2.5 or
PM10 hot-spot analysis under today's final rule.
    The following are examples of projects that are not an air quality
concern under Sec.  93.123(b)(1)(i) and (ii) of this final rule:
     Projects that do not meet the criteria under Sec.
93.123(b)(1), such as any new or expanded highway project that
primarily services gasoline vehicle traffic (i.e., does not involve a
significant number or increase in the number of diesel vehicles),
including such projects involving congested intersections operating at
Level-of-Service D, E, or F;
     An intersection channelization project or interchange
configuration project that involves turn lanes or slots, lanes or
movements, that are physically separated. These kinds of projects
improve freeway operations by smoothing traffic flow and vehicle speeds
by improving weave and merge operations, which would not be expected to
create or worsen PM2.5 or PM10 violations; and
     Intersection channelization projects, traffic circles or
roundabouts, intersection signalization projects at individual
intersections, and interchange reconfiguration projects that are
designed to improve traffic flow and vehicle speeds, and do not involve
any increases in idling. Thus, they would be expected to have a neutral
or positive influence on PM2.5 or PM10 emissions.
    Some examples of projects of air quality concern that would be
covered by Sec.  93.123(b)(1)(iii) and (iv) are:
     A major new bus or intermodal terminal that is considered
to be a ``regionally significant project'' under 40 CFR 93.101; \9\ and
---------------------------------------------------------------------------

    \9\ 40 CFR 93.101 defines a ``regionally significant project''
as ``a transportation project (other than an exempt project) that is
on a facility which serves regional transportation needs (such as
access to and from the area outside of the region, major activity
centers in the region, major planned developments such as new retail
malls, sports complexes, etc., or transportation terminals as well
as most terminals themselves) and would normally be included in the
modeling of a metropolitan area's transportation network, including
at a minimum all principal arterial highways and all fixed guideway
transit facilities that offer an alternative to regional highway
travel.''
---------------------------------------------------------------------------

     An existing bus or intermodal terminal that has a large
vehicle fleet where the number of diesel busses increases by 50% or
more, as measured by bus arrivals.
    Again, the above examples are considered to be the most likely
projects that would require a PM2.5 or PM10 hot-
spot analysis under today's final rule.
    Examples of projects that are not an air quality concern under
Sec.  93.123(b)(1)(iii) and (iv) would be:
     A new or expanded bus terminal that is serviced by non-
diesel vehicles (e.g., compressed natural gas or hybrid-electric
vehicles); and
     A 50% increase in daily arrivals at a small terminal
(e.g., a facility with 10 buses in the peak hour).
3. Rationale
    Legal rationale for targeting diesel vehicles. EPA continues to
believe it has discretion to establish the level of PM2.5
and PM10 hot-spot analysis that is necessary to meet
statutory requirements. The Clean Air Act requires that projects not
create new air quality violations, exacerbate existing violations, or
delay timely attainment, but the statute does not specify what type of
analysis is needed to meet these requirements. Therefore, EPA is
finalizing criteria for when hot-spot analyses are required based on
scientific information available on PM2.5 and
PM10 hot-spots, and the Agency's experience in implementing
CO and PM10 hot-spot requirements since 1993 for what level
of analysis is appropriate and worthwhile. As described in Sections
III. and IV., the final rule does not require any hot-spot analysis--
qualitative or quantitative--for all other projects that are not listed
in Sec.  93.123(b)(1) as an air quality concern. These projects are
presumed to meet Clean Air Act requirements and 40 CFR 93.116 without
any explicit hot-spot analysis because EPA concludes based on the
available data that these projects do not have the potential to cause
or contribute to violations.
    The final rule's criteria for hot-spot analyses targets highway and
transit projects that involve a significant increase in diesel vehicle
traffic, since EPA believes that directly emitted particles from diesel
vehicles are the primary consideration for potential PM2.5
and PM10 hot-spots. EPA believes the final rule's criteria
for what projects require hot-spot analyses will ensure that all
projects that have the potential to impact air quality by causing new
violations, making existing violations worse or delaying timely
attainment will be analyzed before they receive federal funding or
approval. The final criteria are consistent with comments that we
received, as discussed further below.
    Technical rationale for targeting diesel vehicles. There is
substantial evidence that sites near concentrated diesel activity can
experience higher concentrations of PM2.5 and
PM10 relative to background sites. EPA has considered
several technical factors in making this conclusion in today's final
rule.
    First, PM2.5 and PM10 diesel emission factors
are significantly higher than gasoline vehicles on a per-vehicle basis,
and direct particulate emissions from gasoline vehicles are more evenly
distributed across all types of vehicle activity. Current
PM2.5 and PM10 exhaust emission factors in
MOBILE6.2 for heavy duty diesel vehicles are approximately 40 to 50
times the rates for gasoline vehicles, on a per vehicle basis. Even
with the implementation of tighter heavy duty vehicle emission
standards beginning in 2007, MOBILE6.2 projects that PM2.5
and PM10 emission factors for heavy duty diesel vehicles
will still be 15 to 20 times the rate for gasoline vehicles in 2015.
Given this difference in emission rates, projects involving increases
in diesel vehicle activity are much more likely to result in conditions
associated with a potential air quality concern.

    Second, several studies examined air quality at sites involving
high-diesel traffic which showed consistently positive findings;
whereas, sites with low diesel traffic showed more inconsistent
results. High levels of vehicle-related particles arise in areas with
high diesel activity, particularly areas with elevated acceleration or
in areas with large numbers of trucks operating for long periods in
close proximity, such as around truck routes, freight terminals or
truck stops. Studies in proximity of vehicular traffic tend to show
that elevated PM2.5 concentrations occur near diesel vehicle
operations, but show less consistent evidence near locations with high
gasoline vehicle operations.
    For example, one recently-published study (Charron et al., 2005)
from a site in downtown London, England, conducted a hierarchical
cluster analysis of PM2.5 concentrations,
PM2.5-10,\10\ CO, oxides of nitrogen (NOX),
light-duty traffic, and heavy-duty traffic. Two clusters were found. CO
clustered with light-duty traffic, in one cluster, while
PM2.5, PM2.5-10, and NOX clustered
with heavy-duty traffic in the other. No clusters indicating changes in
PM2.5 air quality were found for light-duty traffic, which
further supports EPA's rationale for targeting hot-spot analyses for
projects involving significant traffic from diesel vehicles. Another
study (Cyrys et al., 2003) showed that the difference in long-term
average PM2.5 mass between traffic sites and background
sites was equal to the difference in elemental carbon mass between the
two types of sites. Elemental carbon predominantly comes from diesel
exhaust, as demonstrated in several source apportionment studies.
Finally, in a Dutch study (Janssen et al., 2001), concentrations of
PM2.5 measured outside schools were significantly associated
with truck traffic on nearby motorways and distance from the motorways,
but not with car traffic.
---------------------------------------------------------------------------

    \10\ PM2.5-10 considers air quality concentrations of
particles of a diameter of 2.5-10 micrometers.
---------------------------------------------------------------------------

    In addition, studies examining sites with only gasoline vehicle
traffic show much less consistency in results for whether or not such
traffic is a PM2.5 or PM10 air quality concern at
the project level. For example, Kuhn et al. (2005) measured
PM2.5 concentrations at sites 2.5 meters and about 150
meters away from a major freeway in Los Angeles that was restricted to
light-duty vehicle traffic. Traffic volumes during sampling were around
5700 per hour. Differences in average mass concentrations for
PM2.5 between upwind and downwind monitors at one site
ranged from -0.2 [mu]g/m3 for particles with 180-2500 nm
diameters to 1.8 [mu]g/m3 for smaller particles. At another
site, total particle mass under 180 nm diameter differed by 3.8 or 4.1
[mu]g/m3, depending on measurement method. Due to the
relative inconsistency of PM2.5 results across the study
area, this study demonstrates that gasoline vehicles do not appear to
reliably create higher PM2.5 concentrations that could
create or worsen an air quality violation in a localized area.
    These and other studies provide consistent evidence for elevated
PM2.5 concentrations associated with nearby diesel vehicle
activity, while for gasoline vehicle activity, the evidence is less
consistent. Because diesel vehicle activity tends to be more
concentrated along truck routes, freight terminals, and truck stops,
the air quality impact of direct PM2.5 emissions from these
vehicles is likely to be more geographically focused. Compared to
diesel vehicles, gasoline vehicles tend to be relatively uniformly
distributed throughout an urban area.
    In conclusion, EPA believes that it is appropriate to only require
PM2.5 and PM10 hot-spot analyses for projects
that involve significant numbers of diesel vehicles, based on current
information and PM2.5 and PM10 air quality
standards. EPA will continue to review and evaluate new research on the
mass and distribution of direct PM2.5 and PM10
emissions from gasoline and diesel vehicles in the future.
    Rationale for specific criteria for identifying projects of air
quality concern. EPA has made several revisions to the criteria in
Sec.  93.123(b)(1) to ensure that PM2.5 and PM10
hot-spot analyses are completed for all projects of air quality
concern. Rather than finalize only the proposed criteria for
PM2.5 and PM10 quantitative analyses, EPA is
finalizing more specific criteria for the types of projects that
require evaluation consistent with the discussions in the proposals and
comments received. The following paragraphs describe in more detail
EPA's rationale for the specific criteria in this final rule.
    First, EPA is finalizing two criteria to specifically target
highway projects that involve significant increases in diesel vehicle
traffic (Sec.  93.123(b)(1)(i) and (ii)), so that highway projects of
air quality concern are analyzed and therefore meet statutory
requirements. The final rule requires PM2.5 and
PM10 analyses for ``new or expanded highway projects that
have a significant number of or significant increase in diesel
vehicles,'' and somewhat consistent with a similar criterion for CO
quantitative hot-spot analyses, ``projects affecting intersections that
are at Level-of-Service D, E, or F with a significant number of diesel
vehicles, or those that will change to Level-of Service D, E, or F
because of increased traffic volumes from a significant number of
diesel vehicles related to the project.'' \11\
---------------------------------------------------------------------------

    \11\ EPA notes, however, that the CO criterion in 40 CFR
93.123(a)(1)(ii) focuses on all such intersections. In contrast,
today's final rule only focuses on such intersections involving
significant levels of new diesel traffic.
---------------------------------------------------------------------------

    EPA believes that it can finalize these revised criteria for
highway projects of air quality concern based on information provided
in preamble discussions, in the proposals, and comments received as
discussed further below. To omit such highway projects from hot-spot
analyses would not ensure that these projects meet statutory
requirements. See Section VII. for how categorical hot-spot findings
could take into account air quality circumstances for projects of
concern and ultimately eliminate the need for a quantitative analysis
for some individual projects.
    Second, EPA is deleting the previous conformity rule's vague
criteria that would have required quantitative PM2.5 and
PM10 hot-spot analyses for projects that ``are located at
sites at which violations have been verified by monitoring'' and
``which are located at sites which have vehicle and roadway emission
and dispersion characteristics that are essentially identical to those
of sites with verified violations (including sites near one at which a
violation has been monitored).'' EPA also notes that the final rule
deletes a consultation requirement from Sec.  93.105(c)(1)(v) and Sec.
93.123(b)(3) of the previous conformity rule, which were intended to
implement these previous vague criteria. While the air quality
circumstances at a project's location are an important modeling
consideration, these previous regulatory criteria are insufficient to
ensure that all projects of air quality concern are analyzed before
they receive federal funding or approval. The final rule's criteria
will ensure that all projects that have the potential to impact a local
air quality violation will be analyzed. All other projects are not
expected to impact the air quality standards, even in the case where
such a project is located near a violating monitor or is similar to a
project by a violating monitor.
    EPA believes that the critical factor for establishing
PM2.5 and PM10 hot-spot criteria is whether or
not a project's direct PM2.5 or PM10 emissions
could actually cause a new violation or worsen an existing air quality
violation. The previous criteria did not address

specific types of projects that have significant levels of diesel
emissions. Instead, the previous criteria could have resulted in hot-
spot modeling for any project being located near an existing violating
monitor or for any project that is similar to a project that is near an
existing violating monitor, even if the project is not anticipated to
result in enough PM2.5 or PM10 emissions to
impact local air quality. An example of such a project could be a minor
arterial that primarily serves gasoline fueled passenger vehicles. As
discussed above, EPA concludes that quantitative hot-spot modeling for
such a project is not necessary to meet statutory requirements, and
would be a waste of limited state and local resources. Further
discussion on the elimination of these criteria are discussed below in
the response to comments part of this section.
    Next, EPA is finalizing Sec.  93.123(b)(1)(iii) and (iv) relating
to bus and rail terminals to be consistent with its December 2004
supplemental proposal and previous PM10 requirements. EPA
has split the proposed and previous criterion into two separate
criteria since the factors to consider for brand new versus expanded
terminals and transfer points are different. Whereas a new terminal or
transfer point would look at whether the total number of diesel
vehicles was significant, an expansion of an existing terminal or
transfer point would be evaluated based on whether the increase from
current operations was significant for a given project's circumstances.
    Today's action clarifies Sec.  93.123(b)(1)(iii) and (iv) so that
quantitative hot-spot analyses would only be required for such projects
that involve significant increases of diesel vehicle traffic, and not
insignificant vehicle increases with de minimis localized emissions
increases. EPA believes that it can finalize these minor clarifications
to existing PM10 hot-spot requirements and create
PM2.5 requirements as a logical outgrowth of the December
2004 proposal and comments received.
    EPA is also finalizing its proposed new criterion for when
PM2.5 and PM10 hot-spot analyses are completed if
a PM2.5 or PM10 SIP identifies additional
projects of air quality concern for a given area. Since the primary
intent of the Clean Air Act is to ensure consistency between
transportation decisions and SIP air quality objectives, it is
appropriate to require more intensive hot-spot analyses in cases where
the SIP specifically identifies a type of transportation project
location as having the potential to increase local emissions and worsen
air quality.
    This is especially true if the SIP identifies a type of project not
otherwise listed in Sec.  93.123(b)(1) of today's final rule as being
of air quality concern in the circumstances of a particular area. That
is, requiring hot-spot analyses to also be completed for types of
project locations that the SIP identifies will support the SIP's goals
for an individual area in those cases where a state has the information
to identify specific types of locations as potential hot-spot concerns.
Where a state does not have such information, EPA believes that the
other four regulatory criteria included in today's final rule for when
analyses are completed sufficiently cover the cases where it is likely
for a hot-spot to occur.
    EPA again notes that the criterion in Sec.  93.123(b)(1)(v) is
consistent with a similar criterion in Sec.  93.123(a)(1)(i) of the
existing rule's requirements for quantitative CO hot-spot analyses.
That criterion requires quantitative CO hot-spot analyses ``[f]or
projects in or affecting locations, areas, or categories of sites which
are identified in the applicable implementation plan as sites of
violation or possible violation; * * *.''
    Efficient use of state and local resources. Targeting projects of
air quality concern and eliminating qualitative analyses for projects
that are not of concern will also streamline conformity determinations
in PM2.5 and PM10 hot-spot reviews, since the
majority of proposed projects are not of air quality concern. As a
result, the final rule will utilize state and local resources in an
efficient and reasonable manner while still satisfying Clean Air Act
requirements.
4. Response to Comments
    EPA received many comments regarding what projects should be
required to have PM2.5 and PM10 hot-spot analyses
as part of project-level conformity determinations. Many commenters
believed that the existing and proposed criteria for quantitative hot-
spot analyses were insufficient for meeting Clean Air Act requirements.
Others only commented on the proposed changes to a specific criterion.
Many commenters agreed that hot-spot analyses should be focused on
highway and transit projects involving heavy diesel traffic.
Comment
    Many commenters believed that EPA's proposed regulatory criteria
for PM2.5 and PM10 hot-spot analyses were
inadequate. These commenters argued that EPA should specify in the
conformity rule what types of projects are most likely to cause
PM2.5 or PM10 hot-spots, and thus where
quantitative hot-spot analyses should be considered to meet statutory
requirements. For example, several commenters argued that the final
regulatory criteria needed to specifically require hot-spot analyses
for larger highway projects, such as capacity expansions and congested
intersections with diesel traffic. Another commenter believed that
heavy diesel traffic at large toll road entrance areas and transit
tunnel entrances were also a concern, but not specifically addressed by
the proposed criteria. By establishing more specific regulatory
criteria, commenters believed all projects of air quality concern will
meet Clean Air Act requirements by not causing new or more severe or
more frequent violations, or by not delaying timely attainment.
    Some commenters acknowledged that EPA has already adopted objective
criteria for when quantitative hot-spot analyses are required for
certain cases. They cited the current conformity rule's CO quantitative
hot-spot criteria in Sec.  93.123(a)(1)(ii)-(iv) as a good example for
establishing objective criteria for PM2.5 and
PM10 quantitative hot-spot analyses. These commenters also
supported Sec.  93.123(b)(1)(iii) of the previous conformity rule (now
covered by Sec.  93.123(b)(1)(iii) and (iv) of today's final rule).
This criterion, the commenters stated, relied on objective criteria to
be applied for the circumstances of a given project (i.e., the number
of diesel vehicles likely to be in an area).
    Two commenters cited several scientific studies that they believed
showed that highway projects of four lanes or more must be considered
significant and analyzed under the final rule. Commenters believed that
studies confirmed that heavily trafficked highways can be expected to
contribute an increment to urban background of the annual
PM2.5 standard in the range of 1-3 [mu]g/m3 in
neighborhoods near the freeway traffic lanes.
    One study cited by commenters was the ``East Bay Children's
Respiratory Health Study'' (Kim, et al., AJRCCM, Table 2), which showed
that major freeways contribute at least 3 [mu]g/m3 to
PM2.5 concentrations in adjacent neighborhoods studied. In
this study, mean PM2.5 concentrations measured in a school
yard 60 meters downwind from a freeway with annual average daily trips
(AADT) of 190,000 was 15 [mu]g/m3, which was 3 [mu]g/
m3 above the levels reported at the regional scale monitors
operated by air agencies. These commenters concluded that highways of 4
lanes or larger can be expected to

contribute at least 1 [mu]g/m3 or more to local
PM2.5 concentrations. Commenters believed that larger
highway projects of six lanes or more should be expected to change
PM2.5 concentrations even further.
    Commenters also cited other information in their comments, and EPA
notes only a portion of this information here. A study completed by
Dutch researchers (Netherlands Aerosol Programme, October, 2002),
commenters believed, was consistent with the East Bay Children's Health
Study in that highways were estimated to contribute about 3 [mu]g/
m3 at 60 meters from the highway, with the impact tailing
off to about 1 [mu]g/m3 at 100 meters. In addition,
commenters cited an April 2004 research project of an interstate in
downtown Seattle, Washington, where AADT is more than 200,000. The
project found that the annual mean PM2.5 and black carbon
concentrations found 20 meters from the interstate were significantly
higher as compared to another monitoring site 600 meters from the
interstate.
    Further, some commenters urged EPA to add new regulatory criteria
that do not rely upon data from existing monitors for the purpose of
identifying projects that must undergo PM2.5 and
PM10 hot-spot analyses. Commenters believed that EPA's
proposed and previous rule's criteria in Sec.  93.123(b)(1)(i) and (ii)
would not ensure that quantitative analyses would be completed for all
projects of concern, since sufficient air quality monitoring data does
not exist to implement these criteria. Two commenters further stated
that most new major highways, expansions or interchanges will occur at
sites where no relevant ambient air quality data is available, or where
current data does not show a violation (although a violation may occur
when a given project is built). Consequently, the proposed and previous
criteria in Sec.  93.123(b)(1)(i) and (ii), commenters opined, would be
arbitrary and capricious since sufficient data is not available to
identify every potential highway project of concern.
Response
    EPA agrees with the bulk of these comments and has changed the
final rule in part in response to these comments, as described in EPA's
rationale above. As stated above, it is essential that a quantitative
PM2.5 or PM10 hot-spot analysis be performed for
all projects of air quality concern, as stipulated through the final
rule's criteria. EPA accomplishes this in the final rule by (1)
specifically addressing all projects with significant levels of diesel
traffic, and (2) eliminating previous vague criteria that targeted
monitoring locations rather than the air quality impacts of projects of
concern.
    The previous conformity rule's PM10 hot-spot
requirements and the December 2004's proposed regulatory criteria would
not have captured all necessary highway projects and possibly resulted
in an inefficient use of limited state and local resources by requiring
analyses for projects that are not of concern that are located by
violating monitors.
    EPA generally agrees with comments that recommend adopting
regulatory criteria that are similar to the criteria in 40 CFR
93.123(a)(1). EPA suggested such criteria in its preamble for the
November 5, 2003 proposal (68 FR 62712) and December 13, 2004
supplemental proposal (69 FR 72145), where we either cited the CO
criteria or discussed analyzing heavily congested intersections.
However, EPA has decided not to finalize specific regulatory criteria
for quantitative PM2.5 and PM10 hot-spot analyses
similar to Sec.  93.123(a)(1)(iii) and (iv), which apply to projects
identified in the SIP as affecting the top three intersections of the
highest volumes and worst level of service. Such criterion would be
redundant since the final rule already requires hot-spot analyses for
projects at large intersections involving significant diesel traffic
and projects identified in the SIP as an air quality concern.
    EPA has already noted above the types of projects that are most
likely to be considered projects of air quality concern under today's
final rule. For example, new highway or expressway facilities that
serve a significant volume of diesel traffic are considered projects of
air quality concern under today's final rule.
Comment
    Another commenter stressed the importance of selecting appropriate
examples of project locations of potential concern in EPA's future
guidance. This commenter was concerned that the examples given in the
December 2004 supplemental proposal for PM10 hot-spot
analyses under proposed Option B concentrated on diesel exhaust
particulate matter. Although these examples are appropriate for
PM2.5, this commenter believed that localized
PM10 concentrations are more likely to be dominated by re-
entrained road dust.
Response
    The final rule will ensure that re-entrained road dust will be
considered in PM10 hot-spot analyses for projects that have
the potential to create new or worsen existing air quality violations.
EPA has determined that these projects of air quality concern are those
involving significant diesel emissions which is the most critical
factor in applying a PM10 hot-spot requirement, for reasons
already stated in this final rule and the original 1993 conformity
rulemaking (January 11, 1993, 58 FR 3780). In addition, the conformity
rule requires that road dust be included in all PM10 hot-
spot analyses, as described later in this section.
Comment
    Several commenters supported EPA's proposed clarification to the
previous rule's Sec.  93.123(b)(1)(iii) (now covered by Sec.
93.123(b)(1)(iii) and (iv) of the final rule) indicating that
quantitative PM2.5 and PM10 hot-spot analyses
would be required for projects that significantly increase the quantity
of diesel vehicles. EPA also notes that a few commenters supported
targeting projects addressed by this requirement, such as weight
inspection stations and bus terminals with significant diesel traffic.
Commenters also believed that other projects should also be considered
such as transit maintenance yards, truck stops and school bus terminals
and maintenance yards.
Response
    The final rule is generally supportive of these comments. The
interagency consultation process should be used to identify projects
needing PM2.5 and PM10 hot-spot analyses, and
EPA's future quantitative modeling guidance will provide further
information to consider for such analyses. EPA agrees that hot-spot
analyses should be targeted to projects of air quality concern, which
involve projects with significant diesel traffic.
Comment
    Some commenters expressed support for the newly proposed criterion
now in Sec.  93.123(b)(1)(v) of the final rule that would require
PM2.5 or PM10 hot-spot analyses if the SIP
identifies other projects of air quality concern. These commenters
believed that this criterion would support the SIP's air quality goals
and Clean Air Act conformity requirements in the case where a state
identified such projects as a hot-spot concern.
    Two of these commenters, however, did not support this criterion if
it was the sole mechanism for ensuring that projects of concern were
evaluated for potential PM2.5 or PM10 hot-spots.
Commenters strongly objected to proposed options (e.g., Option B for
PM2.5 and PM10 hot-spot analyses after

SIP submission) to rely upon the SIP to solely identify where hot-spot
analyses were required for a variety of reasons. For example,
commenters were concerned that those options depended too heavily on a
SIP that would not be submitted for several years during which time
highway projects of concern would be approved that could impact local
air quality and public health. See Sections III. and IV. of this notice
for further comments regarding the options cited by commenters.
Response
    EPA agrees with these comments, which are addressed by the final
rule as described elsewhere in this notice.
Comment
    Some commenters believed that the MPO and the state or local air
agency should have the opportunity to identify projects to undergo
quantitative hot-spot analyses. One commenter argued that this
authority, which should be specifically recognized in Sec.
93.123(b)(1), is especially important in those portions of
nonattainment and maintenance areas where small increases in emissions
may cause a new violation or interfere with an attainment strategy that
barely achieves attainment.
Response
    EPA agrees that the consultation process--which includes state and
local transportation and air quality agencies--is critical in
transportation conformity determinations. EPA has provided examples and
other information to target projects of air quality concern. Projects
not of air quality concern are not expected to result in new air
quality violations, worsen existing violations or delay timely
attainment of the air quality standards, even in the situations
described by commenters.
Comment
    Some commenters also believed that EPA should define what projects
could be ``significant'' and require PM2.5 and PM10
quantitative hot-spot analyses. There were several variations from
commenters on this theme, depending on the options EPA proposed and
would consider in the development of the final rule. A few commenters
welcomed the opportunity to work with EPA to determine appropriate
criteria for identifying projects that require quantitative analyses.
    Some commenters suggested that EPA establish significance
thresholds or a screening methodology that would define when
quantitative or qualitative hot-spot analyses were required. For
example, commenters cited significance criteria that New York State and
New York City have adopted for identifying projects that have a
``significant'' impact and are required to undergo a detailed impact
analyses and evaluation of mitigation measures for NEPA purposes.\12\
---------------------------------------------------------------------------

    \12\ These commenters included documentation that New York City
has adopted guidance requiring an assessment of mitigation measures
if emissions from a transportation project are expected to add 0.1
[mu]g/m3 annually, or 5.0 [mu]g/m3 daily of
PM2.5 to the ambient air.
---------------------------------------------------------------------------

    Two commenters also proposed that highway projects of concern could
be identified based on specific average daily vehicle trip criteria,
such as:
     An estimate of daily emissions from a given highway
segment based upon aggregated hourly emissions expected from traffic
conditions over the course of current and expected future daily traffic
patterns for the segment; or
     Traffic loads measured as AADT taking into account the
variability in emissions that can result from high or low diesel
vehicle contribution to AADT.
    These commenters provided an example conducted last year by the
Wisconsin Department of Natural Resources that projected that a
proposed warehouse and distribution center at which an average of 235
semi-trailer trucks would arrive and depart each day would contribute,
on average, 1.6 [mu]g/m3 of PM2.5, and potentially more than
2.0 [mu]g/m3, to the annual average PM2.5
standard (Wisconsin DNR memorandum, Revised Air Dispersion Analysis for
PM2.5 Emissions from Roundy's Warehouse and Distribution Center--
Oconomowoc, April 29, 2004).
Response
    EPA agrees that there should be guidelines for further defining
which highway or transit projects are considered to have a significant
number of or a significant increase in diesel vehicles. EPA has
provided some examples in this notice, along with other commenter
suggestions. Any project that will cause such a significant number of
or significant increase in diesel vehicles will require a
PM2.5 or PM10 hot-spot analysis. EPA and DOT are
available for further discussions on a particular project.
Comment
    Some commenters requested EPA guidance on what specifically is
intended by a significant increase in the number of diesel vehicles in
a location under Sec.  93.123(b)(1)(iii) and (iv) of the final rule.
One commenter expressed concern that significance be determined solely
through interagency consultation.
Response
    It is important to consider both the actual number of vehicles
increased at a project location as well as how this increase relates to
existing vehicle fleets. For example, a bus terminal expansion that
increases the number of daily arrivals by more than 50% would be
significant for an existing bus terminal served by a large fleet. In
contrast, a 50% increase in daily arrivals at a small terminal (e.g., a
facility with 10 buses in the peak hour) would not be significant.
Areas should consider the circumstances involved at an individual
project's location, including the total vehicle increase and how such
an increase compares to the size of the existing diesel fleet for a
given project location. Areas should also consider the type of vehicles
that are added to an area either through a brand new or expanded
existing terminal. As noted above, this final rule specifies projects
of air quality concern as terminals or transfer points involving diesel
vehicles. Projects involving new or expanded fleets of compressed
natural gas or hybrid electric vehicles would not be considered to be
projects of air quality concern.
Comment
    Another commenter stated that, for intersections, a clear,
scientifically based criterion for ``highly congested'' is needed. The
commenter gave as examples studies done for the California Department
of Transportation by the University of California, Davis, in the 1990's
which failed to find a clear indication of PM10 hot-spots
near two major intersections with higher traffic volumes and levels of
congestion than in other areas. The commenter stated that it is still
unclear at what level of congestion and volume the potential for an
intersection hot-spot would arise. The commenter believed that
additional research and technical review is needed before reasonable
analysis methods (including changes to emission models to better fit
microscale analysis needs) for such situations can be defined.
Response
    This commenter is referring to the examples of projects provided in
the December 2004 supplemental proposal that could possibly be
identified under an option that solely relied on the SIP to identify
projects needing quantitative hot-spot analyses (e.g., Option B). The
examples included ``highly congested intersections.''
    EPA is finalizing instead a criterion that was discussed in the
November 2003 proposal and is more similar to the

current conformity rule's Sec.  93.123(a)(1)(ii) which involves
projects in CO areas at intersections of Level-of-Service D, E, and F.
However, the final rule only requires PM2.5 or
PM10 hot-spot analyses of such projects involving
significant levels of diesel traffic. This final rule does not require
a PM2.5 or PM10 hot-spot analysis for projects at
intersections of Level-of-Service D, E, and F that are used primarily
by gasoline vehicles. EPA has provided other examples of what a
significant level of diesel vehicles could include elsewhere in this
notice.
Comment
    Another commenter stated that ports and airports should also be
included in the list of projects that require an analysis for potential
PM2.5 and PM10 hot-spots. This commenter felt
that potential air quality impacts from ports and airports need to be
carefully considered to enable economic growth while ensuring
appropriate mitigation of emission increases and that ports, their
transportation support systems, and airports are also often located in
areas with sensitive populations and environmental justice concerns.
Response
    EPA has not addressed port and airport projects funded or approved
by the Federal Aviation Administration (FAA) and other federal agencies
in this final rule, because these types of projects are not covered by
the transportation conformity rule. These projects are covered by the
general conformity rule.
    However, EPA notes that any transit or highway projects that are
intended to service transportation to and from a port or airport
project would be addressed by transportation conformity, and may
require PM2.5 or PM10 hot-spot analyses if they
are a project of air quality concern under Sec.  93.123(b)(1).
Comment
    A commenter supported EPA and DOT developing a list of ``exempt''
projects that would not require quantitative hot-spot analyses. The
commenter also suggested that further consideration should be given to
refine a list of projects or situations that can be tested through
qualitative hot-spot analyses as agreed upon through the consultation
process. One commenter noted that only qualitative PM2.5 and
PM10 hot-spot analyses would be possible prior to the
development and release of quantitative methods.
Response
    EPA has addressed this comment in part by removing the requirement
to perform qualitative hot-spot analyses for projects that are not an
air quality concern. As described in Sections III. and IV., these
qualitative analyses for projects that are not expected to impact air
quality violations are not an efficient use of state and local
resources, in light of past practice indicating that no such analyses
have ever found a hot-spot problem in such areas. EPA agrees with the
commenter that qualitative hot-spot analyses will be required for
projects of concern before quantitative guidance and tools are
available. Finally, future categorical hot-spot findings, as described
in Section VII., could possibly streamline hot-spot requirements
further for certain projects if it is found that additional analyses
are not needed to meet statutory requirements.

C. General Requirements

1. Description of Final Rule
    EPA is retaining for PM10 areas and extending for
PM2.5 areas the general requirements in Sec.  93.123(c) for
hot-spot analyses of projects of air quality concern. EPA did not
propose any substantive changes to these requirements, which are:
     Analyzing the total emissions burden of direct
PM2.5 and PM10 emissions which may result from
the implementation of the project (including re-entrained road dust and
construction dust, as described below), summed together with future
background concentrations;
     Analyzing the entire transportation project, after the
identification of major design features which will significantly impact
local concentrations;
     Using consistent assumptions with those used in regional
emissions analyses for inputs that are required for both analyses
(e.g., temperature, humidity);
     Assuming the implementation of mitigation or control
measures only where written commitments for such measures have been
obtained; and
     Not considering temporary emissions increases from
construction-related activities which occur only during the
construction phase and last five years or less at any individual site.
    Re-entrained road dust would be included in all PM10
hot-spot analyses, since fugitive dust dominates PM10
inventories. EPA has historically required road dust to be considered
in all PM10 conformity analyses. In contrast, road dust
emissions are only to be considered in PM2.5 hot-spot
analyses if EPA or the state air agency has made a finding that such
emissions are a significant contributor to the PM2.5 air
quality problem (40 CFR 93.102(b)(3)). EPA has provided more
information later in this section in response to a comment on including
fugitive dust in PM2.5 or PM10 hot-spot analyses.
    EPA continues to believe that construction dust emissions from a
particular project would not be included in a PM2.5 or
PM10 hot-spot analysis, if such emissions are considered
temporary as defined in Sec.  93.123(c)(5). Further information on
including non-temporary construction emissions for certain projects is
discussed further below.
    EPA is also extending the requirements of Sec.  93.125(a) for all
projects in PM2.5 nonattainment and maintenance areas that
rely on control or mitigation measures in project-level conformity
determinations. As described in the November 2003 and December 2004
proposals, FHWA or FTA must obtain from the project sponsor and/or
operator enforceable written commitments to implement any required
project-level control or mitigation measures, prior to making a
project-level conformity determination for projects in PM2.5
nonattainment or maintenance areas. The final rule does not revise the
existing commitment requirement for projects in PM10 areas.
    In its previous proposals, EPA had implied that Sec.  93.125(a)
might only be relevant for proposed options that would require
PM2.5 and PM10 hot-spot analyses. EPA is
clarifying in today's preamble that Sec.  93.125(a) applies to all
project-level conformity determinations that involve projects with
control or mitigation measures that are:
     Identified as conditions for the NEPA process;
     Identified as conditions for a transportation plan or TIP
conformity determination's regional emissions analysis; or
     Used in a project-level hot-spot analysis.
Of course, today's final rule does not require any control or
mitigation measures for project-level conformity determinations in
PM2.5 areas; it simply requires that sufficient commitments
be in place if there happen to be any measures for a given project
before a PM2.5 project-level conformity determination is
made.
    EPA does not expect this clarification in today's preamble to have
a practical impact on project implementation. Today's final rule does
not change the regulatory text that was proposed for Sec.  93.125(a).
Again, adding a reference for PM2.5 to Sec.  93.125(a)
simply provides

added enforcement of measures if any exist for projects in
PM2.5 areas.
    Today's final rule also includes minor clarifications with respect
to PM2.5 to various parts of the current conformity rule
that are consistent with existing CO and PM10 hot-spot
analysis requirements. For example, EPA is adding PM2.5 to
the current rule's ``hot-spot analysis'' definition in Sec.  93.101.
This and other clarifications were proposed in regulatory text in the
December 2004 supplemental proposal.
2. Rationale
    EPA is extending to PM2.5 areas the current conformity
rule's general requirements for conducting PM10 hot-spot
analyses. These changes for PM2.5 do not substantively
change these PM10 provisions of the current conformity rule
(e.g., Sec. Sec.  93.123(c) and 93.125(a)), but rather just apply these
requirements to PM2.5. These provisions are intended to
produce credible analyses for whether project emissions create new or
worsen existing air quality violations. EPA intends that the hot-spot
analysis compare concentrations with and without the project based on
modeling conditions in the analysis year. The hot-spot analysis is
intended to assess possible violations due to the project in
combination with changes in background levels over time. Estimation of
background concentrations may take into account the effectiveness of
any anticipated control measures if they are enforceable and
creditable.
    EPA also believes that conformity should address long-term
emissions from the transportation system, and that conformity should
not prevent project implementation because of temporary emissions
increases. In addition, the NEPA process provides the most appropriate
forum to analyze construction-related emissions impacts and to
establish mitigation measures. PM2.5 and PM10
hot-spot analyses would not have to include construction-related
activities which cause temporary and self-correcting increases in local
concentrations, which are defined under the existing and today's final
rule as those which occur only during the construction phase and last
five years or less at any individual site. See the preamble for the
January 1, 1993 proposal (58 FR 3779-3780) and November 24, 1993 final
rule (58 FR 62212-62213) for further information regarding the intent
and rationale for these general hot-spot requirements.
3. Response to Comments
    EPA received a limited number of comments on the general
requirements for performing PM2.5 and PM10 hot-
spot analyses.
Comment
    One commenter supported the EPA proposal that Sec.  93.123(c)
requirements should be maintained in an effort to develop continuity
between analysis efforts. The commenter further agreed that Sec.
93.125(a) requirements should be applied to PM2.5 hot-spot
analyses so that the implementation of any project-level control or
mitigation measure is assured.
Response
    EPA agrees for the reasons cited by the commenter. The existing
requirements have a proven track record since the original 1993
conformity rule for providing credible and reasonable hot-spot
analyses.
Comment
    However, another commenter disagreed with EPA's proposal to apply
Sec. Sec.  93.123(c)(4) and 93.125(a) to PM2.5 hot-spot
analyses since PM2.5 SIP measures are already enforceable as
a matter of law based on the Clean Air Act and the NEPA process. The
commenter argued that EPA should reevaluate its previous rulemaking
decisions on compliance with PM2.5 and PM10 SIP
control measures in 40 CFR 93.117 because these requirements are
duplicative and unnecessary.
Response
    EPA disagrees with this comment and believes that the conformity
rule is the appropriate context for meeting all Clean Air Act
conformity requirements. Implementation and enforcement of measures can
be an important part of reducing emissions for projects, when
necessary. Without assurance that such measures will be implemented, it
is not possible to accurately predict what emissions may be for
project-level conformity determinations, and whether or not projects
meet statutory requirements.
    EPA also acknowledges that, though these control measures would
already be applicable to such projects through NEPA and other
mechanisms, including commitments to them in conformity determinations
provides an additional enforcement tool that, at times, may be
necessary.
Comment
    EPA also received comments regarding when Sec.  93.123(c) requires
fugitive dust to be included in PM2.5 or PM10
hot-spot analyses. Some commenters did not believe that road dust
should be included in PM2.5 or PM10 hot-spot
analyses due to lack of state and local information on the importance
of dust emissions on air quality. They also argued that road dust
should only be included in PM2.5 hot-spot analyses if road
dust has been found to be a significant contributor to the
PM2.5 air quality problem (40 CFR 93.102(b)(3)). Commenters
submitted several documents that supported their judgement that further
research was needed to make decisions regarding significance of road
dust for PM2.5 areas. The commenters agreed with the
existing conformity rule's provisions for using the interagency
consultation process for deciding whether road dust is significant for
a given PM2.5 area.
    Another commenter believed that EPA's December 2004 supplemental
proposal was incorrect in stating that there could be cases where
highway and transit construction emissions from an individual project
would be included in a PM2.5 or PM10 hot-spot
analysis pursuant to Sec.  93.123(c)(1). This commenter also cited
Sec.  93.123(c)(5)'s requirement that PM hot-spot analyses not include
temporary increases in emissions caused by construction-related
activities that last 5 years or less at any individual site.
Response
    EPA agrees with some of these comments. In the preamble to the
December 2004 supplemental proposal, EPA described applying Sec.
93.123(c)(1) requirements to PM2.5 or PM10 hot-
spot analyses while including re-entrained road dust and construction
emissions in such analyses only ``as applicable'' (69 FR 72146).
However, EPA did not elaborate on this caveat in its proposal, so
further clarification in today's notice is warranted. Whether or not to
include road or construction dust in PM2.5 or
PM10 emissions analyses are addressed by different
provisions in the existing conformity rule.
    Section 93.102(b)(3) states that re-entrained road dust is to be
considered in any PM2.5 conformity determination, including
PM2.5 hot-spot analyses, if road dust has been found to be a
significant contributor to the PM2.5 air quality program in
a given area. In its July 1, 2004 final rule, EPA highlighted this
requirement in the context of including such dust emissions in plan and
TIP regional emissions analyses. However, Sec.  93.102(b)(3) defines
more broadly what types of emissions are considered in all types of
conformity determinations for a given pollutant and precursor, and
consequently, only requires PM2.5 hot-spot analyses to
include road dust emissions if such emissions have been found
significant

through a finding of significance prior to the PM2.5 SIP or
as part of an adequate PM2.5 SIP motor vehicle emissions
budget.
    However, EPA disagrees that re-entrained road dust would not be
included in a PM10 hot-spot analysis, when performed in a
PM10 nonattainment or maintenance area. Since the 1993
conformity rule was promulgated, EPA has intended for road dust
emissions to be included in all conformity analyses of direct
PM10 emissions because fugitive dust from roadways and other
sources dominate PM10 emissions inventories. To that end,
the conformity rule does not include an exception for when road dust
emissions are not included in PM10 hot-spot analyses, like
the exception for such emissions in PM2.5 analyses in 40 CFR
93.102(b)(3). By definition, PM10 includes larger particles
from fugitive dust including roadway sources, whereas the role of re-
entrained road dust for PM2.5 air quality issues is less
clear (November 5, 2003, 68 FR 62709).
    As described above, EPA continues to believe that construction dust
emissions would not be included in PM2.5 and PM10
hot-spot analyses, if such emissions are considered temporary as
defined by Sec.  93.123(c)(5). In most cases, EPA anticipates that
construction emissions would not be included in hot-spot analyses
because they would be considered temporary. However, there may be
limited cases where a large project is constructed over a longer time
period where it may be appropriate to include any non-temporary
construction emissions, when an analysis year is chosen in which
construction of the project is still occurring.
Comment
    Another commenter believed that PM2.5 and
PM10 hot-spot analyses need to meet existing requirements
for up-to-date and reasonable conformity analyses. The commenter
specifically cited 40 CFR 93.110 and 93.122 as requiring the latest
planning assumptions in conformity analyses and reasonable assumptions
regarding land use projections in regional emissions analyses.
Furthermore, the commenter believed that EPA should clarify that hot-
spot analyses must be based on honest and accurate assumptions and
include trip distribution and land use changes in order to meet
statutory requirements.
    The commenter also argued that project analyses are currently
inadequate because they rely on unrealistic assumptions for no-build
cases, and ultimately, understate emissions impacts. This commenter
believed that almost all transportation agencies apply the growth and
land use assumptions from the build case also to the no-build case,
which was found to be inappropriate in a previous court decision. The
commenter cited EPA's January 2001 guidance entitled, ``Improving Air
Quality Through Land Use Activities,'' which recommends the interagency
consultation be used for agencies to agree to use the most reasonable
and best available assumptions.
Response
    EPA agrees that PM2.5 and PM10 hot-spot
analyses must be based on the latest planning and land use development
assumptions before and after a project is expected to be implemented in
a given analysis year. To do otherwise would not produce credible hot-
spot analyses that meet Clean Air Act requirements. Section
93.105(c)(1)(i) of the existing conformity rule requires the
interagency consultation process to be used to evaluate and choose
models and associated methods and assumptions to be used in
PM2.5 and PM10 hot-spot analyses.

VI. Timing of PM2.5 and PM10 Quantitative Hot-
spot Analyses and Development of Future Guidance

A. Description of Final Rule

    EPA is finalizing its proposal to not apply quantitative
PM2.5 and PM10 hot-spot requirements until EPA
releases quantitative modeling guidance and announces in the Federal
Register that such requirements are in effect. This action extends the
existing conformity rule's Sec.  93.123(b)(4) requirements for
PM10 areas to also cover PM2.5. EPA will consult
with conformity stakeholders when developing its future quantitative
modeling guidance.

B. General Rationale

    EPA is finalizing the proposal because we continue to believe that
appropriate tools and guidance are necessary to ensure credible and
meaningful quantitative PM2.5 and PM10 hot-spot
analyses. Before such analyses can be performed, technical limitations
in applying existing motor vehicle emission factor models must be
addressed, and proper federal guidance for using dispersion models for
PM hot-spot analysis must be issued, as described further below.

C. Rationale and Response to Comments About Motor Vehicle Emissions
Factor Models

1. Rationale
    On February 24, 2004, EPA released MOBILE6.2 as the approved motor
vehicle emissions factor model for SIP and conformity purposes outside
of California, where EMFAC2002 is the most recently EPA-approved model
for that state. With the release of MOBILE6.2, state and local
transportation agencies now have an approved model for estimating
regional PM2.5 and PM10 emissions factors in SIP
inventories and regional emissions analyses for transportation
conformity. However, MOBILE6.2 has significant limitations that make it
unsatisfactory for use in microscale analysis of PM2.5 and
PM10 emissions as necessary for quantitative hot-spot
analyses. To understand those limitations it is necessary to compare
how emissions of CO, hydrocarbons (HC), and NOX are
calculated in MOBILE6.2 with the methods used to calculate
PM2.5 and PM10 emissions.
    EPA has incorporated CO, HC, and NOX emissions in MOBILE
from the very first version of the model. EPA has had many years to
collect data and refine the methodologies used to estimate emissions of
these pollutants. As a result, MOBILE6.2 incorporates adjustments for
the effects on CO, HC, and NOX emissions of environmental
conditions, such as temperature, humidity, altitude; fleet
characteristics, such as age distribution and mileage accumulation by
age; activity impacts, such as speed and road type (i.e, driving
cycle); and fuel characteristics, such as fuel sulfur level. These
adjustments are incorporated as local input options in MOBILE6.2 and
changes in any of them can have significant affects on emissions of CO,
HC, and NOX as determined by the model. Therefore,
quantitative CO hot-spot analyses have been required since the original
1993 conformity rule because the MOBILE model has been appropriate for
these analyses in project-level conformity determinations for CO areas
(40 CFR 93.123(a)).
    In contrast, emissions estimation for PM2.5 and
PM10 was only added to MOBILE6.2 in 2004.\13\ Because EPA
has not since then developed sufficient databases of vehicle
PM2.5 or PM10 emissions that are as complete as
those for CO, HC, and NOX, the algorithms used in MOBILE6.2
for estimating PM emissions are much simpler than those

used for CO, HC, and NOX. While MOBILE6.2 has the same input
options for PM as for the other pollutants, most of those input options
do not have any affect on PM2.5 or PM10 emission
estimates calculated by the model. For example, there are no
temperature, humidity, or altitude corrections in MOBILE6.2 for
PM2.5 or PM10. Speed, driving cycle, engine
starts, and all of the other activity input options similarly have no
affect on PM2.5 or PM10 emissions in MOBILE6.2.
The only conditions that do affect PM2.5 or PM10
emissions in MOBILE6.2 are fleet and fuel characteristics.
---------------------------------------------------------------------------

    \13\ PM10 emissions were previously estimated using
an EPA model called PART5, which had the same limitations described
here for MOBILE6.2.
---------------------------------------------------------------------------

    EPA has already determined that these limitations are not a
substantial problem for regional scale emissions estimation needed for
PM2.5 and PM10 SIP inventories and regional
emissions analyses for conformity. MOBILE6.2 does account for the
effects of vehicle standards and the impacts of fleet turnover. Growth
in activity is also accounted for in projections of future VMT which
are multiplied by emission factors to derive emissions inventories.
While it is desirable to include other activity effects such as speed
and driving cycle, differences in these inputs are generalized over a
larger area in a regional analysis. Even in the absence of data and
methods to derive adjustment factors for these effects, EPA believes
that MOBILE6.2 is an adequate tool for evaluation of PM2.5
and PM10 emissions at the regional level.
    However, at the micro-scale level needed for hot-spot analyses,
these limitations become very significant. Activity factors such as
speed, driving cycle, and number and distribution of engine starts per
day do have an important impact on actual PM2.5 or
PM10 emissions from motor vehicles. Most, if not all,
transportation projects that would need to be analyzed would result in
changes in these activity levels that would need to be incorporated in
credible hot-spot analyses. For example, the construction of a highway
interchange would likely result in significant changes to average
speeds, driving cycles of vehicles, idling time, etc. in the immediate
vicinity of the interchange. The effects of these changes are an
important and necessary component of estimating the impact of the new
interchange on nearby PM2.5 or PM10
concentrations, but none of these changes can be accounted for in the
currently available emissions factor models.
    Likewise, the mitigating effects of potential control measures that
smooth traffic flow, such as synchronization of traffic signals, cannot
be accounted for in existing models. These limitations apply even to
projects where changes in vehicle speed are less of an issue. For
example, long duration idling emissions are also poorly accounted for
in MOBILE6.2. As a result, it is not an adequate tool for assessing the
localized impacts of individual projects such as bus, rail or freight
terminals, or potential mitigation measures for incorporation into such
projects.
    EPA is working to resolve limitations in MOBILE6.2 through a major
data collection and model development effort. As part of that effort,
EPA is collecting data on real-world environmental and activity effects
on emissions for all pollutants, including PM2.5 and
PM10. The next version of EPA's motor vehicle emissions
model (called MOVES) will incorporate PM2.5 or
PM10 adjustments for environmental and activity conditions
(including long-duration idling) that are currently missing in
MOBILE6.2, and relevant to hot-spot modeling as described above. MOVES
will be specifically designed to work at both the regional and micro-
scale level. EPA believes that MOVES will provide the level of detail
needed for credible and meaningful PM2.5 or PM10
hot-spot analysis. A draft version of MOVES that incorporates new
emissions information for motor vehicles is expected in 2006 with a
final version in 2007.
    EPA also believes that both an appropriate motor vehicle emissions
factor model and EPA's guidance on applying air quality models is
necessary before quantitative PM2.5 and PM10 hot-
spot modeling guidance can be required in California. While EPA has
approved EMFAC2002 for PM2.5 and PM10 regional
emissions analysis in California, we do not currently have enough
information about how it handles vehicle activity effects on
PM2.5 or PM10 emissions to make a determination
of its applicability to quantitative PM2.5 and
PM10 hot-spot analyses. EPA will evaluate the applicability
of EMFAC2002 for quantitative PM2.5 and PM10 hot-
spot analyses in the context of EPA's future quantitative modeling
guidance.
2. Response to Comments
    EPA received several comments directed at the application of motor
vehicle emissions models in quantitative PM2.5 or
PM10 hot-spot analyses.
Comment
    Some commenters agreed that the current modeling tools do not have
the ability to evaluate PM2.5 for hot-spot analyses
adequately. They believed that MOBILE6.2 is insensitive to many
variables likely to affect localized PM2.5 emissions,
specifically speed and drive cycles. One commenter supported EPA's
development of MOVES since it will provide for better PM2.5
and PM10 analyses in the future. Some of these commenters
also noted that implementors will now have time to gather data and
obtain experience for conducting future quantitative analysis of PM
emissions.
Response
    EPA agrees with these comments for the reasons given above and
therefore has not required quantitative hot-spot analyses until
appropriate tools and EPA guidance are available.
Comment
    Other commenters strongly disagreed with EPA's proposed approach to
extend Sec.  93.123(b)(4) to PM2.5 hot-spot analyses.
Commenters argued that the absence of emissions factors was the single
greatest obstacle to modeling PM2.5 motor vehicle emissions,
and now that EPA has released MOBILE6.2, there is no basis for further
delaying a requirement that emissions from highways be quantified and
assessed as part of a project-level conformity determination. Most of
these commenters argued that continuing to delay quantitative
PM2.5 or PM10 hot-spot analyses for
transportation projects is unjustified, given that great advancements
in modeling tools have been made since the publication of the original
1993 conformity rule. Because EPA has required the use of MOBILE6.2 for
SIP development and regional emissions analyses, one commenter also
believed it would be unlawful not to require its use in
PM2.5 and PM10 hot-spot analyses.
Response
    EPA disagrees with these commenters based on the technical
limitations of using MOBILE6.2 for hot-spot analyses as discussed in
detail above. The use of MOBILE6.2 in hot-spot analyses will produce
inaccurate results in some cases. For example, a project that would
actually result in lower net emissions due to traffic flow
improvements, would appear to result in an increase in emissions in an
analysis done using MOBILE6.2 if the project also resulted in some
increase in activity. This is because MOBILE6.2 is insensitive to the
effects of changes in speed for PM2.5 or PM10. At
the same time, a project that actually results in increased emissions
due to increased long-duration idling, might appear to have no impact
on emissions given that MOBILE6.2 does not properly account for long-
duration

idling emissions. Further, EPA does not believe that it can be assumed
that a model is appropriate for a hot-spot analysis simply because EPA
has approved a model for regional analyses. Any model EPA approves must
be appropriate for the use to which it will be put. For all the reasons
explained above, MOBILE6.2 is not appropriate for PM2.5 or
PM10 hot-spot analyses despite the fact that it may be
appropriate for regional analyses of those pollutants.
Comment
    One of these commenters also referenced text from pages 40-41 of
EPA's August 2004 ``Technical Guidance on the Use of MOBILE6.2 for
Emission Inventory Preparation'' as evidence that MOBILE6.2 can be used
to estimate emissions from individual transportation projects.
Response
    The commenter incorrectly interpreted the specific text referenced
in the MOBILE6.2 technical guidance that describes how the model can be
used to account for differences in emissions by roadway type. Although
this input accounts for the differences in emissions in stop-and-go
driving as on an arterial street and continuous speed driving as on a
freeway, those differences only apply to the estimation of CO, HC, and
NOX emissions. PM10 and PM2.5
emissions are not effected by these inputs. As described above,
differences in emissions by the type of driving that will occur are
critical to analyses of individual projects and MOBILE6.2 cannot
account for these differences for PM2.5 or PM10
hot-spot analyses.

D. Rationale and Response to Comments About Dispersion Models and Other
Modeling Issues

1. Rationale
    In order to complete appropriate hot-spot modeling, EPA needs to
specify which air quality dispersion models are appropriate for
transportation projects and provide additional guidance for estimating
PM2.5 and PM10 concentrations at the local level.
Dispersion models estimate air quality concentrations based on the
emissions produced by a particular project (which will be provided in
part through models like MOVES) and the background concentrations
assumed at a project location. There are currently many different
dispersion models that are being used for air quality modeling,
including modeling of localized air quality impacts for other
pollutants. However, as described further below, EPA believes that it
must first release quantitative modeling guidance that describes how to
apply existing air quality dispersion models to result in credible
PM2.5 and PM10 hot-spot analyses.
2. Response to Comments
Comment
    Many commenters supported the final rule approach because they
believed that EPA guidance is essential for highlighting which
dispersion models are appropriate and for addressing other modeling
issues. Some commenters requested clarification on whether hot-spot
analyses would be compared to the PM2.5 or PM10
annual or daily standards. Some commenters agreed that guidance is also
necessary for the projection of future travel activity levels and
future background concentrations. Other commenters believed that the
issuance of guidance would provide modeling consistency and eliminate
redundancy across the country.
Response
    EPA agrees with these comments for the reasons cited by the
commenters. EPA believes that the future hot-spot modeling guidance
will provide information that will be essential for addressing PM-
specific modeling issues, which some commenters supported. In addition,
as stated elsewhere in this section, EPA also believes that its future
development of the MOVES model is essential to providing credible
PM2.5 and PM10 hot-spot analyses.
Comment
    Other commenters believed Sec.  93.123(b)(4) was originally
included in the 1993 conformity rule with EPA's commitment to issue
timely guidance on quantitative hot-spot analyses, which has not
occurred. These commenters were very concerned that finalizing the
proposal would create a loophole for delaying quantitative PM hot-spot
analyses for projects that could negatively impact air quality and
public health. These commenters believed that adequate dispersion
models are already available for PM2.5 and PM10
quantitative hot-spot analyses, and no additional EPA guidance is
needed before requiring such analyses. Another commenter believed that
quantitative hot-spot analyses of transportation projects should either
apply immediately upon promulgation of the final rule or within a short
period of time after promulgation (e.g., 120 days), if EPA has not yet
issued quantitative modeling guidance by that time.
Response
    Although EPA agrees with commenters that quantitative
PM2.5 and PM10 hot-spot analyses are critical for
considering the public health implications of transportation projects,
we strongly disagree with commenters' conclusions. EPA is not using the
release of its future hot-spot modeling guidance to delay credible and
meaningful quantitative PM2.5 or PM10 hot-spot
analyses. In fact, requiring such analyses now without having all
models and EPA's guidance available could result in analyses that are
not credible and waste limited state and local resources.
    EPA agrees that adequate air quality dispersion models may be
available, but having such models is only one aspect of conducting
credible PM2.5 or PM10 hot-spot analyses. As
described in C.1. of this section, adequate dispersion models alone are
not enough to conduct credible PM2.5 or PM10 hot-
spot analyses; adequate motor vehicle emissions factors and guidance
for using motor vehicle emissions factor and dispersion models is also
needed. The results from dispersion models would not be reliable for
PM2.5 and PM10 estimates if the emission factor
models used to provide input (such as MOBILE6.2) do not provide
sufficient detail to distinguish changes in activity factors.
    Nevertheless, even if the emission factor models did provide this
level of detail, EPA would still need to provide guidance on the
application of dispersion models in determining whether a
PM2.5 or PM10 hot-spot will occur. Dispersion
models are complicated tools that, if used incorrectly, could result in
incorrect conclusions about the impact of an individual project's
localized concentrations. For example, the location of model receptors
is particularly important in dispersion modeling of PM2.5
and PM10 emissions. If the receptors are predominately
upwind of the project being analyzed, it could lead to false
conclusions about the likelihood of a violation. Guidance is also
needed on making model output comparable to the relevant form of the
air quality standards, and to EPA regulations and guidance for
PM2.5 monitoring for the 24-hour and annual PM2.5
standards.
    Another important factor in dispersion modeling is the choice of
meteorological data used in PM2.5 and PM10 hot-
spot analyses. Areas need guidance in how to choose meteorological
conditions that are properly representative of conditions

that might result in a violation. Without proper guidance, areas might
choose to use meteorological data that lead to under-or over-predicting
the likelihood of a violation.
    Guidance is also necessary to describe how the projection of future
travel activity levels and future background concentrations can be used
as inputs to dispersion modeling. Projects need to be analyzed based on
assumptions that they are fully utilized, or are experiencing maximum
predicted emissions, rather than projections of use when they first
open. Likewise, dispersion modeling has to take into account projected
changes in background PM2.5 and PM10
concentrations.
    These are just a few examples of the kinds of issues that modelers
will face when developing PM2.5 and/or PM10 hot-
spot analyses. EPA is currently researching these kinds of issues so
that currently available dispersion models can be applied appropriately
for PM2.5 and PM10 hot-spot analyses. Without
having all necessary models and detailed guidance, EPA cannot have
reasonable assurance that the results of dispersion modeling in hot-
spot analyses will be consistent and credible throughout the country,
and ensure that all projects will meet statutory requirements.
Comment
    Two commenters cited a recent paper \14\ on modeling toxic
emissions which they interpret as providing strong evidence that
currently available dispersion models are suitable for estimating local
PM concentrations. Toxic air pollutants include non-reactive gases that
would disperse like CO, and others that are aerosols that would
disperse as particles in the ambient air.
---------------------------------------------------------------------------

    \14\ Robert G. Ireson, ``Dispersion Modeling for Mobile Source
Air Toxics Exposure,'' (January 9, 2005) Transportation Research
Board's 84th Annual Meeting of Air Quality Management Consulting.
---------------------------------------------------------------------------

Response
    As discussed in the previous response, EPA agrees that current
dispersion models may be suitable for estimating PM2.5. or
PM10 concentrations, provided that accurate emissions inputs
are available for the dispersion models and that the models are used
properly, as will be addressed in EPA's future quantitative modeling
guidance. The limitations of existing emissions information for
localized analysis have already been discussed in detail in C.1 of this
section. The need for additional guidance on dispersion models is
further discussed in this section.
Comment
    Three commenters recommended that new regulatory language be added
to the conformity rule to require that ``state-of-the-art'' modeling
tools be used to conduct PM2.5 or PM10 hot-spot
analyses as determined through the interagency consultation process. By
having model selection determined through consultation, a commenter
believed that EPA would have an opportunity to provide guidance on
specific details even if formal guidance has not yet been issued.
Response
    EPA disagrees with this general approach. The significant technical
limitations in MOBILE6.2 discussed in C.1. of this section cannot
simply be resolved through interagency consultation, and EPA's future
modeling guidance will ensure that credible analyses are conducted.
However, once an appropriate motor vehicle emissions model and EPA's
future guidance is available, EPA agrees that the consultation process
will play an important role in performing PM2.5 or
PM10 hot-spot analyses. Section 93.105(c)(1)(i) of the
conformity rule already requires that consultation be used to evaluate
and choose models and associated methods and assumptions for hot-spot
analyses. Such consultation must be consistent with the use of EPA-
approved motor vehicle emissions models and our future guidance.
Comment
    One commenter stated that PM2.5 source apportionment
techniques should first be improved, and that models that simulate the
chemistry and transport of PM2.5 should be validated at the
microscale level before hot-spot modeling is required. This same
commenter also noted that MOBILE6.2 estimates that low-sulfur diesel
fuel and cleaner vehicles, due to the phase-in of Tier 2 and federal
heavy duty engine standards, will dramatically reduce PM2.5
emissions in the future. Therefore, this commenter implied that
PM2.5 hot-spots may not be as much of a concern once
PM2.5 source apportionment techniques and chemical/
dispersion models are available, since by that time on-road mobile
sources may only represent a small fraction of PM2.5
emissions in nonattainment areas.
Response
    PM source apportionment is not a relevant technique for project-
level air quality modeling, because it pertains to current, observed
outdoor PM measurements. The air quality impacts of those
transportation projects that are relevant to a conformity determination
are estimated in the future, when actual monitoring data is not
available. As such, source-oriented models that use emissions estimates
and run them through an air quality model are the only appropriate
tools for projecting future-year impacts of transportation projects.
The second part of this comment suggests that chemical transport models
are required for microscale analysis. However, over the time during
which air parcels pass from a transportation project to a location
several hundred meters downwind, where PM hot-spots could be a concern,
there is insufficient time for chemical reactions to affect PM mass
concentrations. Dispersion models have been used for this purpose in
the past, and have been evaluated in the scientific literature. The
commenter is correct that PM2.5 emissions from motor
vehicles are expected to decline in the future as a result of new
vehicle standards and fuels. However, the impact of those new standards
is gradual and does not preclude the possibility of PM hot-spot
problems in the future.
Comment
    Two commenters noted that existing tools have already been used in
a few cases for localized NEPA analyses for PM10, which they
argued supported the mandatory application of these tools for all
PM10 and PM2.5 hot-spot analyses.
Response
    EPA disagrees. While it is true that these analyses were done on a
voluntary basis, it is not clear how well these analyses would stand up
to review if there was a mandatory requirement for quantitative
PM2.5 or PM10 hot-spot analyses, for the
technical reasons discussed above.

E. Process and Timing for Developing Guidance

    As described above, EPA is working to resolve the limitations in
MOBILE6.2 as part of the development of MOVES, EPA's new emissions
model for mobile sources. As described above, EPA is currently
collecting and analyzing data, while simultaneously developing the
MOVES model itself. A draft version of MOVES that incorporates new
emissions information for motor vehicles is expected in 2006 with a
final version in 2007. MOVES will undergo both stakeholder and peer
review. More information on MOVES can be found at http://www.epa.gov/otaq/ngm.htm.
 EPA

will also release SIP and transportation conformity policy guidance for
the final release of MOVES, which among other issues will describe the
grace period for using MOVES in regional and hot-spot conformity
analyses.
    EPA has also dedicated significant resources to conducting research
that will be used in the development of the Agency's future guidance
for quantitative PM2.5 and PM10 hot-spot
analyses, which would be available when states are able to begin using
MOVES. This guidance will discuss how MOVES and dispersion models can
be used to complete quantitative PM2.5 and PM10
hot-spot analyses for the transportation projects specified in today's
final rule.
Comment
    Several commenters agreed that stakeholders should be involved
during the development of the future quantitative hot-spot modeling
guidance. One commenter suggested that this guidance should be
developed through a formal process similar to rulemakings. Another
commenter recommended that EPA subject future hot-spot models and
guidance to peer review.
Response
    EPA agrees that stakeholder input will be important in the guidance
development process and intends to provide for such input, but has not
yet determined exactly what that process will be. However, EPA does not
intend to develop its future hot-spot modeling guidance through notice-
and-comment rulemaking, since this has not been our past practice for
such guidance or even for motor vehicle emissions factor models like
MOBILE6.2.

F. Suggestions for Future Guidance

Comment
    Several commenters had specific recommendations for items that
should be included in EPA's future quantitative PM2.5 and
PM10 hot-spot guidance. Examples of recommendations include:
     A screening procedure for reducing the number of