Responses to Comments Not Addressed in the 

Preamble to the Final Rule:

Transportation Conformity Rule PM2.5 and PM10

Amendments 

February 5, 2010

Docket ID No. EPA-HQ-OAR-2008-0540
Docket ID No. EPA-HQ-OAR-2008-0540

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Comment:

One commenter was concerned that the grace period for newly designated areas 

would not leave sufficient time for their agency to complete and adopt a TIP based on the

agency’s schedule. The commenter wrote that if the designations were made in “October 

2009,” and the one-year grace period expires in “December 2009,” there would be 

insufficient time to demonstrate conformity and adopt the 2010 TIPs. 

Response: 

The preamble to the final rule clarifies the applicable dates. The commenter’s 

assertion that the grace period expires in December of 2009 is incorrect. EPA’s final rule 

designating areas nonattainment for the 2006 PM2.5 NAAQS was published in the 

Federal Register on November 13, 2009, and effective December 14, 2009. The oneyear conformity grace period for newly designated areas begins on December 14, 2009, 

and ends on December 14, 2010. 

Comment: 

The commenter notes that serious health impacts are associated with exposure to 

fine PM. More than enough research has been done that shows that some types of 

transportation projects can emit enough PM2.5 to cause or contribute to violations of the 

NAAQS. Given the compelling evidence that diesel exhaust may be the most hazardous 

of all PM components, it is imperative that EPA fulfill its responsibility to control PM2.5

emissions from transportation projects. 

Response:

EPA has fulfilled its responsibility regarding PM2.5 emissions from transportation 

projects by implementing the Clean Air Act conformity requirements for PM2.5. 

Comment: 

One commenter thought that EPA’s proposed option to define the baseline year 

related to the SIP or AERR process would not reduce EPA’s need to issue guidance in the 

future. 

Response:

EPA intends to issue guidance to clarify the baseline year for any future new or 

revised PM2.5 NAAQS. Such guidance will be needed to explain how the regulation 

finalized today (which defines the baseline year with respect to the AERR) should be 

implemented for a specific new or revised PM2.5 NAAQS. However, today’s regulation 

removes the need for EPA to revise its baseline year regulation for any future new or 

revised PM2.5 NAAQS.
Docket ID No. EPA-HQ-OAR-2008-0540

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Comment:

A commenter suggested that if EPA finalizes the proposed option 2 for the 

baseline year, EPA should align the baseline year for the 2008 8-hour ozone NAAQS 

with the baseline year for the 2006 PM2.5 NAAQS. 

Response:

EPA did not propose to revise the baseline year for any future new or revised 

ozone NAAQS, and therefore this comment is outside the scope of today’s action. 

Comment:

A commenter that supported the option finalized in today’s rule noted that EPA’s 

Office of Air Quality Planning and Standards has not recommended a single SIP 

modeling base year as a reason for their support of this option.

Response:

EPA notes that there is no requirement that the baseline year for the conformity

baseline year test and the base year used for SIP modeling be the same year. The 

baseline year for the baseline year test for the 2006 PM2.5 areas is 2008, as described in 

the preamble of today’s rule. 

Comment:

One commenter noted that either interim emissions test is adequate as long as the 

same emissions model and assumptions are used for the build scenario and the 

comparison scenario, i.e., either the no-build scenario or the baseline year. 

Response: 

EPA agrees that the same model has to be used for both the build case and the 

comparison case, given differences in model results between MOBILE6.2 and MOVES 

using the same or similar inputs. EPA believes it is unlikely that any area would want to 

use different models for the build and comparison cases in a single regional emissions 

analysis given the additional time involved. In any case, models for conformity analyses 

must be decided through the interagency consultation process, of which EPA is a 

member, and that consultation process will help ensure that consistent models and 

assumptions are used.

Comment:

The commenter noted that areas are likely to need to use interim tests in 

upcoming years because most areas do not have adequate or approved budgets for the 

1997 PM2.5 NAAQS. In addition, this commenter noted that the court’s remand of the 

CAIR program still needs to be addressed. This commenter also noted that the 

introduction of MOVES will require rerunning some inventories for consistency

purposes. 
Docket ID No. EPA-HQ-OAR-2008-0540

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Response: 

EPA agrees that many areas will need to use one of the interim emissions tests 

because adequate or approved budgets are not yet available for the 1997 PM2.5 NAAQS. 

EPA’s response to the CAIR remand is outside the scope of today’s rulemaking. 

In areas that have adequate or approved budgets for the 1997 PM2.5 NAAQS, SIPs 

may need to be updated using MOVES. EPA believes that the 2006 PM2.5 NAAQS 

nonattainment areas must use MOVES in developing SIPs for this NAAQS, therefore 

such inventories will not need to be redone when MOVES is required for transportation 

conformity (i.e., at the end of the two-year MOVES grace period). 

Comment:

One commenter was concerned that there is no SIP strategy designed to reduce 

emissions near roadways to the levels needed to attain the NAAQS, and EPA’s proposed 

interpretation of CAA 176(c)(1)(B)(iii) fails to require the highway project to reduce 

emissions in the area affected by the project. The commenter suggested that if EPA were 

to modify its SIP guidance to require states to model the incremental impact of highway

emissions near highways, and develop a control strategy designed to remedy these 

violations, then EPA’s interpretation of CAA 176(c)(1)(B)(iii), to require an air quality

assessment focused on whether emissions from the proposed project would cause or 

contribute to new violations or worsen existing violations, would be reasonable. 

However, the commenter believes that EPA has created a set of SIP policies that allows 

states to ignore elevated levels of PM2.5 and resulting NAAQS violations near highways. 

And, as long as these policies remain in effect, the commenter believes that there is no 

basis for interpreting (B)(iii) as allowing projects to proceed if emissions from those 

project continue to cause or contribute to future NAAQS violations.

Response:

For the reasons described in the preamble to today’s action, EPA disagrees that its 

regulations fail to satisfy CAA section 176(c)(1)(B)(iii). Further, the commenter’s 

assertions regarding the alleged shortcomings of the SIP process are outside the scope of 

today’s rulemaking.

Comment: 

One commenter was concerned that introduction of MOVES would result in an 

inability to pass conformity. This commenter states that the area experienced three nonconformity determinations from 1996-2003, because SIP budgets were initially calculated 

using MOBILE4 but subsequent EPA models effectively doubled calculated emissions, 

resulting in “technical” mismatch with budgets. This commenter stated that they are not 

yet able to assess their potential situation because MOVES is not yet available.

Response: 

Because a new emissions model can produce different emissions results, the 

conformity rule includes a provision for a grace period before the new model must be 

used for conformity determinations. This grace period can be from three months to two 
Docket ID No. EPA-HQ-OAR-2008-0540

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years, depending on the degree of change between the existing model and the new model. 

In the case of MOVES, EPA intends to provide the maximum length grace period of two 

years. 

EPA released MOVES2010 in December 2009, and will be establishing a twoyear grace period, which should give areas sufficient time to address issues. 

Furthermore, EPA believes SIPs for the 2006 PM2.5 NAAQS must be developed using 

MOVES. EPA is providing SIP and conformity guidance for the transition to the 

MOVES model, as well as other information and training regarding the use of MOVES.

See EPA’s website: http://www.epa.gov/otaq/models/moves/trainingsessions.htm for 

information about upcoming training sessions. Also note that other MOVES related 

guidance, including user guides and other technical information is available on EPA’s 

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

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

Comment:

One commenter suggested that air quality modeling process used in transportation 

conformity should be reformed to use the most recent air quality data available, rather 

than prediction-based models. 

This commenter also suggested that emissions budgets have a built-in level of

flexibility, such as a 10 to 15 percent cushion, to allow for increases in emissions. 

Third, this commenter suggested that hot-spot analysis should be removed from 

the regulations.

Response:

EPA did not in this rulemaking propose any regulatory revisions addressing air 

quality modeling, and therefore the first comment is outside the scope of this rulemaking. 

However, EPA believes that the current requirements to model future transportation 

activity and resulting emissions is required by the Clean Air Act. Section 176(c)(2)(A) of 

the Act requires that “emissions expected from implementation of such plans and 

programs are consistent with estimates of emissions from motor vehicles and necessary

emissions reductions contained in the applicable air quality implementation plan...” In 

other words, conformity is to examine future transportation sector emissions, rather than 

an area’s overall air quality, which is affected by not just the transportation sector but 

other sources of emissions as well as topographical and meterological factors. 

Furthermore, EPA does not believe that it is possible to use an area’s current air 

quality data to estimate emissions as distant as 20 years in the future. As described 

above, an area’s current air quality data results from all sources of emissions. While the 

transportation sector’s emissions are included, they result from current levels of vehicle 

miles traveled (VMT) and the emissions characteristics of the vehicle fleet on the road 

today. Neither VMT nor vehicle emissions will be the same in the future as they are 

today. The conformity rule’s requirements for preparing a regional emissions analysis 

result in a reasonable estimate of future emissions that result from planned transportation. 

EPA’s new emissions model, MOVES, does include the most recent data about 

vehicle emissions under different conditions. EPA believes that this model improves the 

accuracy of predicted emissions. 
Docket ID No. EPA-HQ-OAR-2008-0540

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Further, EPA did not propose in this rulemaking any revisions to the conformity

budget test regulations and did not propose substantive changes to the hot-spot 

requirements. Therefore, the comments on those issues are outside the scope of today’s 

action.