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Transportation Conformity Practices in Complex Areas

MPOs with Multiple Nonattainment or Maintenance Areas for the Same Pollutant

There are 19 MPOs in 11 States as shown in Attachment D that contain more than one nonattainment and/or maintenance area, or portions of such areas, for the same pollutant. MPOs may be in nonattainment for more than one pollutant (i.e., ozone and CO); however, this discussion does not focus on those areas. MPOs with multiple nonattainment or maintenance areas for the same pollutant face special challenges that include:

SIP Issues:

Different SIP requirements may apply to each nonattainment or maintenance area depending on the classification of the area. For example, higher classified ozone areas are subject to more stringent control measures such as enhanced inspection and maintenance programs and potential transportation control measures, while a lower classified area may not be subject to those measures. Different classifications can also complicate the conformity process several ways. For example, different SIP submission or revision schedules for each nonattainment or maintenance area may result in different conformity determination triggers that the MPO must comply with, as well as different attainment and/or milestone years.

MPO regional emissions analyses must be consistent with the motor vehicle emissions budgets in SIPs. In many cases, each nonattainment and maintenance area may have its own budget. However, nonattainment and maintenance areas may contain sub-area budgets. In those cases, the regional emissions analyses must be consistent with the appropriate sub-area budgets.

Budgets for separate nonattainment/maintenance areas cannot be combined in the conformity process by the MPO. However, the State and local air agencies, in the development of the SIP, may choose to combine inventories within a metropolitan area for different nonattainment/maintenance areas and develop a single motor vehicle budget in the SIP for the MPO. In this case, where the SIP identifies a "combined" budget, the MPO may demonstrate conformity for this single budget.

Also, it should be noted that conformity for each nonattainment and maintenance area can be determined separately. For example, if an MPO contains multiple nonattainment areas, but cannot demonstrate conformity for one of the areas, it can still determine conformity for the other area(s).

In addition, eight of the MPOs in this category are part of Multi-State Nonattainment and Maintenance Areas (see also Attachment A). These are:




New Jersey Transportation Planning Agency

New York-New Jersey-Long Island, NY-NJ-CT


South Jersey Transportation Planning Organization

Philadelphia-Wilmington-Atlantic City, PA-NJ-MD


Delaware Valley Regional Planning Commission

New York- New Jersey-Long Island, NY-NJ-CT

PM2.5 24-Hour, 2006

Philadelphia-Camden Co, PA-NJ


Chicago Metropolitan Agency for Planning

Chicago-Naperville, IL-IN-WI


COG of the Central Naugatuck Valley

New York-N. New Jersey-Long Island, NY-NJ-CT

8-hour ozone (2008 std.)

Housatonic Valley Council of Governments

New York-N. New Jersey-Long Island, NY-NJ-CT

8-hour ozone (2008 std.)

Lower Connecticut River Valley Council of Governments

New York-N. New Jersey-Long Island, NY-NJ-CT

8-hour ozone (2008 std.)

Greater Bridgeport Regional Council

New York-N. New Jersey-Long Island, NY-NJ-CT


Another issue occurs when the nonattainment or maintenance area is larger than the MPO planning area and therefore includes a donut area. Four of the MPOs in this category-the Council of Governments of the Central Naugatuck Valley, the Housatonic Valley Council of Elected Officials, , the Wasatch Front Regional Council and Southwestern Pennsylvania Commission -- are part of nonattainment or maintenance areas with donut areas. For more information, please see Nonattainment and Maintenance Areas with "Donut" Area(s) and Attachment C.

Institutional Arrangements:

Where multiple nonattainment or maintenance areas are within the planning boundaries of a single MPO, there may be multiple air agencies that must be part of the interagency consultation process. Interagency consultation works in these areas because it encourages ongoing communication among the key partners. The following are some examples of institutional arrangements and tools that assist in interagency consultation:

In Colorado, the North Front Range MPO has two CO Maintenance areas, Fort Collins and Greeley, within the MPO’s planning boundary. The MPO operates a travel model for the region and supplies transportation inputs to the air quality analysis conducted by the Colorado Air Pollution Control Commission. Prior to conducting a conformity analysis, the North Front Range MPO-works cooperatively with an Air Quality Interagency Coordination Group (ICG),consisting of membership from the Federal Highway Administration (FHWA), Federal Transit Administration (FTA), Environmental Protection Agency (EPA), Colorado Department of Transportation (CDOT), and the Air Pollution Control Division (APCD), to review the assumptions and analysis.

The State of Connecticut presents a unique case. With regard to the 2008 8-hour ozone standard and the 1997 1-hour standard, the entire state is classified as Nonattainment with two designated areas: the New York-N. New Jersey-Long Island, NY-NJ-CT area and the Greater Connecticut area. Within these two nonattainment designations there are 3 MPOs that have both nonattainment areas within their planning boundaries:

In addition there are two designated CO Maintenance Areas -the New Haven-Meriden-Waterbury and the New York-N. New Jersey-Long Island, NY-NJ-CT 'that are within the state, but fully within one MPO's planning boundaries (Greater Bridgeport Regional Council).The Connecticut Department of Transportation coordinates air quality conformity analysis on behalf of these MPOs. Connecticut DOT engages in an interagency consultation process with the MPOs, EPA, FTA, FHWA, and the Connecticut Department of Environmental Protection. CTDOT develops traffic activity inputs using the Connecticut statewide travel demand model.

Analysis issues:

Decisions about which agency takes the lead on travel demand and emissions modeling need to be made as well as coordination on schedules for updating assumptions. A key scheduling issue is keeping the timelines for conformity straight for each of the nonattainment or maintenance areas within the MPO area. SIP submittals should be coordinated through interagency consultation with the MPO so that conformity determination triggers can be anticipated and appropriately planned for.

As noted in Attachment D, in 12 of MPOs with multiple nonattainment and/or maintenance areas, the MPOs take the lead for both travel demand and emissions modeling. In the other 6 areas, different arrangements have evolved for conducting the analysis. For the Southern California Association of Governments (SCAG), the MPO (SCAG) conducts the travel modeling and the Air Quality Management District conducts the emissions analysis for 8-Hour Ozone and PM10; but for 24-Hour PM 2.5 the MPO takes the lead for both travel demand and emissions modeling. And, as noted above, in Connecticut, the State DOT takes the lead on both travel and emissions modeling.

Updated: 10/20/2015
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