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Federal Register / Vol. 86, No. 195 / Wednesday, October 13, 2021 / Proposed Rules 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, FHWA, and FTA to demonstrate that an areas regional transportation plans 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 emissions budgets budgets contained in submitted or approved control strategy SIPs and maintenance plans.42
These control strategy SIPs and maintenance plans typically set budgets for criteria pollutants and/or their precursors to address pollution from cars and trucks. Budgets are generally established for specific years and specific pollutants or precursors. PM10

maintenance plan submittals should identify budgets for transportationrelated PM10 emissions in the last year of the maintenance period.43
For budgets in a maintenance plan to be approvable, they must meet, at a minimum, the EPAs adequacy criteria.44 To meet these requirements, the budgets must be consistent, when considered with emissions from all other sources, with maintenance of the NAAQS and reflect all the motor vehicle control measures relied upon for the maintenance demonstration.
The EPAs process for determining adequacy of a budget consists of three basic steps: 1 Notifying the public of a SIP submittal, 2 providing the public the opportunity to comment on the budget during a public comment period, and 3 making a finding of adequacy or inadequacy. The process for determining the adequacy of a submitted budget is codified at 40 CFR
93.118f. The EPA can notify the public
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by either posting an announcement that the EPA has received SIP budgets on the EPAs adequacy website,45 or via a Federal Register notice of proposed rulemaking when the EPA reviews the adequacy of a maintenance plan budget simultaneously with its review and action on the SIP submittal itself.46
The Indian Wells Second Maintenance Plan includes budgets for direct PM10 for the last year of the maintenance Plan 2025 and an interim year 2020. The applicable source categories included in the budgets include vehicle emissions including exhaust, brake wear, and tire wear, entrained dust from vehicle travel over paved and unpaved roads, and road construction dust. To develop the budgets, the District also rounded up the motor vehicle emissions estimates to the nearest tenth of a ton and included a safety margin.47 The 2020 and 2025
annual average day conformity budgets for PM10 are provided in Table 6.

TABLE 6TRANSPORTATION CONFORMITY BUDGETS FOR THE INDIAN WELLS VALLEY PM10 AREA
PM10 tpd, annual average Source category
2020

Vehicular Exhaust, Tire, and Brake Wear a
SAFE Rule Adjustment
Re-Entrained Paved Road Dust
Re-Entrained Unpaved Road Dust
Road Construction Dust
Safety Margin
Total b
Motor Vehicle Emissions Budget c

2025
0.04
0.00
0.11
0.13
0.03
0.0
0.31
0.40

0.04
0.00
0.12
0.13
0.10
0.10
0.49
0.50

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a This reflects the adjustment factor for the Safer Affordable Fuel-Efficient SAFE Vehicle Rule part one 84 FR 51310, September 27, 2019
using EMFAC2017.
b Values from California Emissions Projection Analysis Model v1.00 may not add up due to rounding.
c Motor vehicle emissions budgets calculated are rounded up to the nearest tenth of a tpd.
Source: Indian Wells Second Maintenance Plan, Table 5.

CARB developed the on-road mobile portion of the emissions inventory for the maintenance plan using Californias on-road mobile source emissions projection model, EMFAC2017, and vehicle activity data provided by the KCOG from its 2019 Federal Transportation Improvement Program, as amended July 2019. The EMFAC2017
model calculated tire wear, brake wear, and exhaust emissions. Paved road dust emissions were estimated using AP42
with California-specific silt loading
data.48 The unpaved road dust emissions were estimated using CARBs methodology 7.10, updated in 2012 for non-farm roads. The road construction dust emissions were estimated based on road miles constructed according to data from KCOG.
As discussed in the March 10, 2006
final transportation conformity rulemaking, unlike the exception for paved and unpaved road dust emissions in PM2.5 analyses in 40 CFR
93.102b3, the conformity rule does
not include an exception for PM10 for paved and unpaved road dust emissions to be determined significant. The EPA
intends 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.
The budgets in the Indian Wells Second Maintenance Plan, therefore, include paved and unpaved road emissions.
Regional PM10 emissions analyses for transportation conformity
42 Control strategy SIPs refer to reasonable further progress and attainment demonstration SIPs. 40
CFR 93.101.
43 Transportation-related emissions of VOC and NOX must also be specified in PM10 maintenance plans if the EPA or the state find that transportation-related emissions of one or both of these precursors within the nonattainment area are a significant contributor to the PM10 nonattainment problem and has so notified the MPO and the U.S.
Department of Transportation DOT, or the
applicable SIP or SIP revision submission establishes an approved or adequate budget for such emissions as part of the reasonable further progress, attainment, or maintenance strategy. 40
CFR 93.102b2iii. Neither of these conditions apply to the Indian Wells PM10 maintenance area.
44 40 CFR 93.118e4.
45 40 CFR 93.118f1.
46 40 CFR 93.118f2.
47 The text of the Plan identifies the safety margin for VOC in 2020 only. However, Table 5 in the Plan
indicates that the safety margin is for PM10
emissions. CARB confirmed via email that the reference to VOC in the text is a typographic error and that the safety margin is for PM10 emissions.
See email dated February 4, 2021, from Nesamani Kalandiyur, CARB, to Karina OConnor, EPA Region IX, Subject: RE: Question Regarding Indian Wells 2nd Maintenance Plan.
48 AP42 is an EPA document that includes a compilation of emissions factors.

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