In addition to the regional analysis criteria and requirements applied to all areas at all times (as discussed in Chapter 5), and in order to demonstrate conformity, PM-2.5 nonattainment and maintenance areas are required to follow these specific criteria, as stated in the transportation conformity rule,
40 CFR §93.122(d)
In all areas not otherwise subject to paragraph (b) of this section, regional emissions analysis must use those procedures described in paragraph (b) of this section if the use of those procedures has been the previous practice of the MPO. Otherwise, areas not subject to paragraph (b) of this section may estimate regional emissions using any appropriate methods that account for VMT growth by, for example, extrapolating historical VMT or projecting future VMT by considering growth in population and historical growth trends for VMT per person. These methods must also consider future economic activity, transit alternatives, and transportation system policies.
Areas without network models may project vehicle miles traveled (VMT) using any appropriate methods that account for VMT growth by, for example, extrapolating historical VMT or projecting future VMT by considering growth in population and historical growth trends for VMT per person. These methods must also consider future economic activity, transit alternatives, and transportation system policies. All VMT estimates must be "calibrated" to HPMS. Also, all methods related to VMT estimations must be decided through interagency consultation.
40 CFR §93.122(b)(3)
Highway Performance Monitoring Systems (HPMS) estimates of vehicle miles traveled (VMT) shall be considered the primary measure of VMT within the portion of the nonattainment or maintenance area and for the functional classes of roadways included in HPMS, for urban areas which are sampled on a separate urban area basis. For areas with network-based travel models, a factor (or factors) may be developed to reconcile and calibrate the network-based travel model estimates of VMT in the base year of its validation to the HPMS estimates for the same period. These factors may then be applied to the model estimates of future VMT. In this factoring process, consideration will be given to differences between HPMS and network-based travel models, such as differences in the facility coverage of the HPMS and the modeled network description. Locally developed count-based programs and other departures from these procedures are permitted subject to the interagency consultation procedures of §93.105(c)(1)(i).
The requirements for regional analysis in PM2.5 nonattainment and maintenance areas are listed below:
In addition to the criteria listed in 40 CFR 93.109(b) - Table 1 of the transportation conformity rule, the conformity determination for PM2.5 nonattainment or maintenance areas is also based on the criteria specific to the nonattainment areas and are summarized in Exhibit 9-1. In order to demonstrate conformity, PM2.5 nonattainment and maintenance areas need to perform "conformity tests" using their regional emissions analysis. Detailed discussion of these requirements is provided in the transportation conformity rule and in Chapter 5.
|Requirements||Sec. (§)||Applicable Time Period|
|All PM2.5 nonattainment and maintenance areas||Latest planning assumptions
Latest emissions model
TCMs (for transportation plan/ TIP) and projects not from a plan/TIP
93.113 (b) -(d)
|PM2.5 nonattainment and maintenance areas, if an adequate or approved SIP budget exists||Emissions budget test||93.118||After EPA has declared a SIP motor vehicle emissions budget to be adequate for transportation conformity purposes.|
PM2.5 nonattainment and maintenance areas, if no adequate or approved SIP budget exists
Interim emissions test (build-no-greater-than-no-build OR no-greater-than-2002 test)
No regional emissions analysis is required
|93.119||Prior to adequate SIP budgets. If there is no approved motor vehicle emissions budget from an applicable implementation plan and no adequate motor vehicle emissions budget from a submitted control strategy implementation plan revision or maintenance plan (93.109(i)(2)).
For previous and existing air quality standards (e.g., 1-hour ozone, 8-hour ozone, PM10 and carbon monoxide (CO)), areas typically have been required to examine a typical summer or winter day because areas were violating a standard established for a time period of 24 hours or less. As a result, these areas have developed on-road motor vehicle SIP inventories, motor vehicle emissions budgets ("budgets"), and regional emissions analysesfor transportation conformity determinations using modeling inputs and parameters that were specific to a typical day within a particular season. However, all areas currently designated nonattainment for PM2.5are violating the annual standard for this pollutant. In order to be consistent with this standard, these areas must develop annual emission inventories for the purpose of developing SIP budgets and demonstrating transportation conformity. In August 2005, EPA released guidance on how to develop these annual inventories. 
A. For the purposes of this question, we assume that the boundaries of the 8-hour ozone area and the PM2.5 area are exactly the same.
When an area is subject to transportation conformity, it must show that its transportation plans, TIPs, and projects conform before they can be adopted or approved.
Conformity of plans and TIPs
There are several steps for the area to show its plan and TIP conform. Briefly:
Step 1: The area must determine which years are to be analyzed (requirements are specified in the conformity rule) and which assumptions and models are to be used. These decisions are made through interagency consultation.
Step 2: The future VMT from the planned transportation system is estimated in each of the analysis years.
Step 3: Emissions that result from that level VMT are estimated using the latest emission factor model (MOBILE6.2 except in California, where EMFAC2002 is used).
Step 4: Emissions are compared to the relevant test. The budget test is used when areas have a SIP for a pollutant; the interim emissions test(s) are used before areas have SIPs.
Step 5: The MPO makes a conformity determination, including public comment. FHWA/FTA make final conformity determinations to complete the process.
For ozone, the emissions that must be examined in conformity are VOC and NOx (40 CFR §93.119(f)(1-2).
For PM2.5, the emissions that must be examined in conformity are direct PM2.5. The precursor NOx is required, unless the EPA Regional Administrator and the director of the State air agency have made a finding that emissions of NOx from within the area are not a significant contributor to the PM2.5 nonattainment problem and have so notified the MPO and DOT (40 CFR §93.119(f)(9)). The precursors VOC, SOx, and/or ammonia (NH3) are required if the EPA Regional Administrator or the director of the State air agency has made a finding that such precursor emissions from within the area are a significant contributor to the PM2.5 nonattainment problem and has so notified the MPO and DOT (40 CFR §93.119(f)(10)). Reentrained road dust is required to be included in the direct PM2.5 emissions only if the EPA Regional Administrator or the director of the State air agency has made a finding that emissions from reentrained road dust is a significant contributor to the PM2.5 nonattainment problem and has so notified the MPO and DOT (40 CFR §93.119(f)(8)). Construction-related fugitive dust is required to be included in the direct PM2.5 emissions only if the SIP identifies it as a significant contributor to the nonattainment problem (40 CFR §93.122(f)(1-2)).
In some cases, Steps 1 and 2 may be the same for both ozone and PM2.5, that is, no additional work would be required. However, once areas have SIPs for both ozone and PM2.5, analysis years may no longer exactly coincide and areas may have to run an additional analysis year as a result of being designated for both pollutants.
Additional work for Step 3 may be required if an area is nonattainment for both ozone and PM2.5, compared to an area that is designated only for ozone. For example, the emissions factor model will need to be run once using summertime conditions for ozone, and may need to be run separately for PM2.5 using a different season's or seasons' conditions. Note that in a case where an area has a travel model that is able to capture seasonal differences in VMT generated, Step 2 may need to be run multiple times as well - once for summertime for ozone, and possibly for a different season or seasons for PM2.5. In August 2005, EPA released emissions inventory guidance for how to analyze annual PM2.5 emissions.
Effort that does not need to be duplicated, though, is the interagency consultation process needed (Step1) and public consultation in Step 5.
Related issues to be considered:
Conformity of projects
In an ozone area, the project level conformity determination consists simply of checking to see that there is a conforming plan and TIP in place, and the project comes from that plan and TIP.
In a PM2.5 area, those two checks must be made but there are additional steps that may have to be taken. First, after a PM2.5 SIP is approved, the project must comply with any PM2.5 control measures in the PM2.5 SIP. Second, EPA issued PM2.5 and revised PM10 hot spot analyses requirements in March 2006. This Guide had not been updated to reflect those changes. A hot-spot analysis is an estimation of a likely future localized pollutant concentrations and a comparison of those concentrations to the air quality standards.
40 CFR §93.119(f)(8)
Reentrained road dust in PM2.5 areas only if the EPA Regional Administrator or the director of the State air agency has made a finding that emissions from reentrained road dust within the area are a significant contributor to the PM2.5 nonattainment problem and has so notified the MPO and DOT.
40 CFR §93.122(f)(1)-(2)
 Guidance for Creating Annual On-Road Mobile Source Emissions Inventories for PM2.5 Nonattainment Areas for Use in SIPs and Conformity, EPA, August 2005 (See Appendix S)
 Conformity Information to Inform PM2.5 Designations, EPA, October 14, 2004