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Federal Register / Vol. 86, No. 183 / Friday, September 24, 2021 / Proposed Rules
contingency measures. Without a protective finding, the final disapproval would result in a conformity freeze, under which only projects in the first four years of the most recent conforming Regional Transportation Plan RTP and Transportation Improvement Programs TIPs can proceed. During a freeze, no new RTPs, TIPs, or RTP/TIP
amendments can be found to conform.240 Under this protective finding, however, the final disapproval of the contingency measures does not result in a transportation conformity freeze in the San Joaquin Valley PM2.5
nonattainment area.
If the State chooses to withdraw the contingency measure element with respect to the 1997 24-hour PM2.5
NAAQS prior to our final action on the SJV PM2.5 Plan for that NAAQS, we would take no final action either to approve or to disapprove that element.
G. Motor Vehicle Emission Budgets 1. Statutory and Regulatory Requirements Section 176c of the CAA requires federal actions in nonattainment and maintenance areas to conform to the goals of the states SIP to eliminate or reduce the severity and number of violations of the NAAQS and achieve timely attainment of the NAAQS.
Conformity to the SIPs goals means that such actions will not: 1 Cause or contribute to violations of a NAAQS, 2
worsen the severity of an existing violation, or 3 delay timely attainment of any NAAQS or any interim milestone.
Actions involving Federal Highway Administration FHWA or Federal Transit Administration FTA funding or approval are subject to the EPAs transportation conformity rule, codified at 40 CFR part 93, subpart A. Under this rule, metropolitan planning organizations MPOs in nonattainment and maintenance areas coordinate with state and local air quality and transportation agencies, the EPA, the FHWA, and the FTA to demonstrate that an areas regional transportation plans RTPs and transportation improvement programs conform to the applicable SIP.
This demonstration is typically done by showing that estimated emissions from existing and planned highway and transit systems are less than or equal to the motor vehicle emission budgets MVEBs or budgets contained in all control strategy SIPs. Budgets are generally established for specific years and specific pollutants or precursors and must reflect all of the motor vehicle 240 40

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control measures contained in the attainment and RFP demonstrations.241
Under the PM2.5 SIP Requirements Rule, Serious area PM2.5 attainment plans must include appropriate quantitative milestones and projected RFP emissions levels for direct PM2.5
and all PM2.5 plan precursors in each milestone year.242 For an area designated nonattainment for the 1997
PM2.5 NAAQS before January 15, 2015, the attainment plan must contain quantitative milestones to be achieved no later than three years after December 31, 2014, and every three years thereafter until the milestone date that falls within three years after the applicable attainment date.243 As the EPA explained in the preamble to the PM2.5 SIP Requirements Rule, it is important to include a post-attainment year quantitative milestone to ensure that, if the area fails to attain by the attainment date, the EPA can continue to monitor the areas progress toward attainment while the state develops a new attainment plan.244 Although the post-attainment year quantitative milestone is a required element of a Serious area plan, it is not necessary to demonstrate transportation conformity for 2023 or to use the 2023 budgets in transportation conformity determinations until such time as the area fails to attain the 1997 24-hour PM2.5 NAAQS.
PM2.5 plans should identify budgets for direct PM2.5, NOX, and all other PM2.5 precursors for which on-road emissions are determined to significantly contribute to PM2.5 levels in the area for each RFP milestone year and the attainment year, if the plan demonstrates attainment. All direct PM2.5 SIP budgets should include direct PM2.5 motor vehicle emissions from tailpipes, brake wear, and tire wear.
With respect to PM2.5 from re-entrained road dust and emissions of VOC, SO2, and/or ammonia, the transportation conformity provisions of 40 CFR part 93, subpart A, apply only if the EPA
Regional Administrator or the director of the state air agency has made a finding that emissions of these pollutants within the area are a significant contributor to the PM2.5
241 40

CFR 93.118e4v.
CFR 51.1012a, 51.1013a1.
243 40 CFR 51.1013a4 and 81 FR 58010, 58058
and 5806358064. Because the area has failed to attain the 1997 24-hour PM2.5 NAAQS by the Serious area attainment date, and it would serve no purpose for the plan to include budgets for the EPA
to evaluate conformity for the dates associated with the Serious area attainment date, the applicable attainment date for the purposes of our evaluation is the section 189d projected attainment date of December 31, 2020.
244 81 FR 58010, 5806358064.
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nonattainment problem and has so notified the MPO and Department of Transportation DOT, or if the applicable implementation plan or implementation plan submission includes any of these pollutants in the approved or adequate budget as part of the RFP, attainment, or maintenance strategy.245
By contrast, transportation conformity requirements apply with respect to emissions of NOX unless both the EPA
Regional Administrator and the director of the state air agency have made a finding that transportation-related emissions of NOX within the nonattainment area are not a significant contributor to the PM2.5 nonattainment problem and have so notified the MPO
and DOT, or the applicable implementation plan or implementation plan submission does not establish an approved or adequate budget for such emissions as part of the RFP, attainment, or maintenance strategy.246
It is not always necessary for states to establish motor vehicle emissions budgets for all PM2.5 precursors. The PM2.5 SIP Requirements Rule allows a state to demonstrate that emissions of certain precursors do not contribute significantly to PM2.5 levels that exceed the NAAQS in a nonattainment area, in which case the state may exclude such precursors from its control evaluations for the specific NAAQS at issue. If a state successfully demonstrates that the emissions of one or more of the PM2.5
precursors from all sources do not contribute significantly to PM2.5 levels in the subject area, then it is not necessary to establish motor vehicle emissions budgets for such precursors.
Alternatively, the transportation conformity regulations contain criteria for determining whether emissions of one or more PM2.5 precursors are insignificant for transportation conformity purposes.247 For a pollutant or precursor to be considered an insignificant contributor based on the transportation conformity rules criteria, the control strategy SIP must demonstrate that it would be unreasonable to expect that such an area would experience enough motor vehicle emissions growth in that pollutant and/
or precursor for a NAAQS violation to occur. Insignificance determinations are based on factors such as air quality, SIP
motor vehicle control measures, trends 245 40 CFR 93.102b3, 93.102b2v, and 93.122f; see also Conformity Rule preambles at 69
FR 40004, 4003140036 July 1, 2004, 70 FR 24280, 2428324285 May 6, 2005 and 70 FR 31354 June 1, 2005.
246 40 CFR 93.102b2iv.
247 40 CFR 93.109f.

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