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Transportation Conformity Practices in Complex Areas

Multi-State Nonattainment and Maintenance Areas

There are 28 multi-State nonattainment or maintenance areas containing 34 Metropolitan Planning Organizations (MPOs) that are nonattainment or maintenance for one or more pollutants including the 2008 ozone standard, as shown in Attachment A. As part of multi-State areas, there are several unique challenges that these MPOs face in the conformity process. These challenges include:

SIP Issues:

Each State is responsible for developing its own SIP. Therefore, decisions are required between the States as to how motor vehicle emissions budgets will be developed for a multi-State nonattainment area. The States could choose 1) to develop SIPs for each State with a single common motor vehicle emissions budget for each pollutant/precursor for the entire multi-State area, or 2) to develop SIPs for each State with separate budgets for each State.

Following the first option, only two multi-State areas have a single common budget for the entire nonattainment/maintenance area (Washington, D.C.-MD-VA maintenance area for CO and nonattainment area for 8 hour ozone, 2008 standard; Logan, UT-ID area for PM 2.5, 2006 standard). For the one MPO within this multi-State area, conformity determinations are based on a regional emissions analysis conducted for the entire multi-State area and tested against the single budget. In other words, the motor vehicle emissions budget is not allocated among each State's portion of the nonattainment or maintenance area.

Twelve multi-state areas develop separate budgets for each state. In five multi-state areas, a separate budget has been developed for at least one state but budgets for all states have not been adopted. In five multi-state areas no budgets are currently in place. Finally, in four multi-state areas, at least one state had a finding of regional insignificance (the Alabama portion of the Chattanooga, TN-GA-AL PM2.5 (1997) area and Huntington-Ashland, WV-KY-OH PM2.5 (1997) area) or a Limited Maintenance Plan for CO (2 cases).

A particularly complex example is a nonattainment/maintenance area which straddles the Missouri and Illinois state line at St. Louis. The Missouri portion consists of 5 counties (Franklin, Jefferson, St. Charles, St. Louis, St. Louis City) in nonattainment for the 2008 eight-hour ozone National Ambient Air Quality Standard (NAAQS) and the 1997 annual PM2.5 NAAQS. The Illinois portion contains three counties that are in nonattainment for the 2008 eight-hour ozone NAAQS and the 1997 annual PM2.5 NAAQS (Madison, Monroe, St. Clair). In addition, part of Madison County in Missouri is nonattainment for PM10 and a partial county (Randolph) in Illinois is nonattainment for the 1997 annual PM2.5 NAAQS. The City of St. Louis and that portion of St. Louis County contained in Missouri within the I-270 loop was classified by USEPA as a limited maintenance area for carbon monoxide in 1999. The Missouri Limited Carbon Monoxide Maintenance Plan option allows plan conformity without a technical analysis. Quantitative conformity analyses are performed by the the East-West Gateway Council of Governments which is the MPO for the remainder of the nonattainment areas.

In the following two examples, separate emission budgets are refined down to the county level in each state. In the first, the Charlotte-Gastonia-Rock Hill nonattainment area, crosses the North Carolina-South Carolina border. It contains a CO maintenance area (Mecklenburg County in NC) and a non-attainment area for the 2008 ozone NAAQS. The ozone non-attainment area consists of Mecklenburg County (including the city of Charlotte) and 6 partial counties around Charlotte (Cabarrus, Gaston, Iredell, Lincoln, Rowan, and Union) in NC and one partial county in SC (York). Emission budgets are in place for CO, VOCs and NOx in Mecklenburg County and for VOCs and NOx in each of the other partial non-attainment counties. Currently, the emission budgets are MOBILE6-based and cover the entire county (except for Iredell County where the emission budget covers a portion of the county).The non-attainment area generally follows the boundaries of four MPOs (Cabarrus-South Rowan Urban Area MPO, Gaston Urban Area MPO, Charlotte Regional Transportation Planning Organization in NC and the Rock Hill-Fort Mill Area Transportation Study in SC) with a few exceptions.

The second example is the Memphis nonattainment area which crosses the Tennessee-Arkansas-Mississippi border. There are two MPO’s covering the non-attainment area. The Memphis Urban Area MPO is a bi-state MPO covering Shelby and Fayette Counties in Tennessee and part of Desoto County in Mississippi. The West Memphis MPO planning boundary includes Crittenden County in AR. The nonattainment boundary contains a CO maintenance area (Shelby County in TN) and a nonattainment area for the 2008 ozone NAAQS. The ozone nonattainment area consists of Shelby County, Crittenden County in Arkansas and part of DeSoto County in Mississippi. Emission budgets are in place for all areas for all relevant pollutants for each county in Tennessee and Arkansas (the VOC and NOx budgets are based on the 1997 ozone standard). There is no emission budget in place in DeSoto County, MS.

Institutional Arrangements:

The challenges of communication and coordination in multi-state nonattainment and maintenance areas increase due to the number of agencies and stakeholders involved in the transportation conformity process. Interagency consultation becomes critical in multi-State nonattainment and maintenance areas. This is especially true the first time through the SIP development and conformity processes when key decisions need to be made about motor vehicle emissions budgets and transportation-related control measures, and about how conformity determinations and regional emissions analyses are conducted.

Thirteen multi-State nonattainment or maintenance areas also contain multiple MPOs. Attachment A lists each MPO that is encompassed by each multi-State nonattainment and maintenance area. For the MPOs that have the final responsibility to make conformity determinations, coordination between the other MPOs and States is vital to a smoothly running process. This is aided by interagency consultation meetings which in some cases occur monthly or on an as-needed basis. The majority of these MPOs use the interagency consultation process to set the schedule for conformity determinations in each respective MPO area and are driven by needed updates to the Long-range Plan and/or Transportation Improvement Plan (TIP). The use of separate budgets for each State in these areas, enables the MPOs within each State to remain independent in scheduling conformity determinations.

The East-West Gateway Coordinating Council (EWGCG), the MPO for the St. Louis urbanized area, covers the entire non-attainment area, with the exception of the partial PM2.5 non-attainment county (Randolph) in Illinois. The Illinois Environmental Protection Agency (Illinois EPA) has prepared MOVES motor vehicle emissions budgets for its portion of the non-attainment area for ozone and the Missouri Department of Natural Resources (DNR) is in the process of developing MOVES motor vehicle emissions budgets for its portion of the non-attainment area for ozone. Both agencies are preparing separate budgets for their state’s portion of the non-attainment area for PM2.5 using MOVES. EWGCG provides travel data to the Illinois EPA and Missouri DNR. The inter-agency consultation process facilitates EGWCG’s work with each state’s air quality agency in developing locality specific inputs (e.g. fuel formulation) and determining the use of default parameters.

The Memphis nonattainment area (TN-AR-MS) conducts transportation conformity through separate processes in each state on separate schedules determined by the transportation agencies in each state. The travel demand model used by the Memphis MPO covers portions of the non-attainment areas in Tennessee and Mississippi. A Memorandum of Understanding is in place between the agencies in Tennessee and Mississippi detailing how the conformity process will be performed for the nonattainment areas in Shelby (TN) and Desoto (MS) Counties. There is also a Memorandum of Understanding in place between the Memphis Urban Area MPO and the West Memphis MPO (in Arkansas) regarding coordination of transportation planning between those two non-attainment MPOs.

In Arkansas, the MPO (West Memphis MPO) does not have a travel demand model, relying instead on traffic counts, HPMS data and growth factors to establish transportation inputs for the conformity analysis.

Transportation conformity determinations for the Charlotte-Gastonia-Rock Hill nonattainment area crossing the NC-SC border, are performed through separate processes by each of the four MPOs on schedules determined by the Interagency Consultation Process, which includes coordination with various transportation and environmental agencies. The conformity determination is performed by North Carolina DOT in the donut counties (Iredell and Lincoln) in the non-MPO portion of the non-attainment area in North Carolina. In South Carolina, one MPO (Rock Hill - Fort Mill Area Transportation Study) is involved with the conformity process, covering the partial county (York) that is part of the non-attainment area. In North Carolina, three MPOs participate in the conformity process. They are: Charlotte Regional Transportation Planning Organization, Gaston Urban Area MPO and Cabarrus-Rowan Urban Area MPO. Although the conformity process in the two states is separate, there is frequent and ongoing sharing of data for planning purposes and interaction among the transportation agencies in the two states. The MPO travel demand model covers the non-attainment area in both states. The MPOs are partners in developing the model and it is housed in and managed by the Charlotte Department of Transportation.

The Logan (UT-ID) nonattainment area transportation conformity analysis is performed by the Cache, UT MPO. The portion of the non-attainment area contained in Idaho does not have an MPO, since it does not meet the required population thresholds. Idaho DOT and air quality agencies provide traffic and emissions data when a conformity determination is required. This is a newly designated non-attainment area with only one conformity determination having been performed by the MPO. Interim tests were used since an emissions budget was not in place as of May 2013.

Analysis issues:

The most significant analysis issue facing MPOs and state DOTs relates to the end of the grace period for the adoption of the MOVES emission model for regional emissions analyses and the end of the grace period to demonstrate conformity to the 2008 ozone standard. It is particularly challenging that both grace periods expire relatively close to one another (March 2013 for the MOVES grace period and July 2013 for the 2008 ozone standard grace period). In general, affected MPOs and state DOTs have adopted conformity determinations to meet the ozone standard and are using MOVES or are transitioning to MOVES to for future determinations. The challenge remains use of MOBILE6-based emission budgets that were developed for the 1997 ozone standard and development of MOVES-based budgets to address the 2008 ozone standard.

EGWCG conducts two separate regional emissions analyses using the separate state budgets to conduct the budget test for the 2008 ozone standard and the Action-2002 Baseline Emissions test to pass conformity for PM2.5 annual standard. Further information on EWGCG’s conformity determinations can be found at: .

The MPO in the South Carolina portion of the Charlotte-Gastonia-Rock Hill ozone nonattainment area completed its first conformity determination using MOVES in June 2013. In North Carolina, the MPOs are preparing to implement a MOVES based conformity determination with new emissions budgets developed using MOVES.

Since a budget for DeSoto County (MS) does not exist in the Memphis nonattainment area (TN-MS-AR) for 2008 8-hour ozone, conformity is established using the 2011 baseline test using MOVES. Nonattainment area MPOs in Tennessee and Arkansas are transitioning to MOVES for the development of county level emission budgets.

MOVES was used to develop the Logan, UT PM 2.5 nonattainment area emissions budgets and the MPO is currently transitioning to use MOVES in their next conformity determination.

Travel demand and emissions modeling - In multi-State nonattainment/maintenance areas, it is most common for MPOs to take the lead in both travel demand and emissions modeling.

Updated: 10/20/2015
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