Skip to content U.S. Department of Transportation/Federal Highway AdministrationU.S. Department of Transportation/Federal Highway Administration

Office of Planning, Environment, & Realty (HEP)
PlanningEnvironmentReal Estate

HEP Events Guidance Publications Awards Contacts

Transportation Conformity Practices in Complex Areas

Multi-MPO Nonattainment and Maintenance Areas

There are 29 nonattainment and maintenance areas that encompass multiple MPOs. These areas include 52 MPOs as shown in Attachment B. These areas face challenges that include:

SIP Issues:

Each State with a multi-MPO nonattainment or maintenance area must determine how motor vehicle emissions budgets will be developed. The State could choose 1) to develop a single motor vehicle emissions budget for the entire multi-MPO area within that State, or 2) to develop separate sub-area budgets for each MPO or some other subset in the multi-MPO area within that State.

If the State chooses to develop a single motor vehicle emissions budget for the entire nonattainment or maintenance area, conformity determinations for each MPO within the area are based on a regional emissions analysis done for the entire multi-MPO area and tested against the single budget. In other words, the motor vehicle emissions budget is not sub-allocated among the MPOs. Eight multi-MPO areas have followed this method, all of which are contained within a single State each. Multi-MPO nonattainment and maintenance areas that have a single budget for the entire area are noted in Attachment B.

Ten of the multi-MPO areas are also multi-State MPOs. (See Multi-State Nonattainment and Maintenance Areas and Attachment A for more information.) In six of these nonattainment areas a hybrid approach to emissions budgeting is utilized where some budgets are established by state and others by MPO boundaries. These hybrid cases are:

In the other four areas, all of which are for 8-hour ozone, subarea budgets are established for each MPO. These are:

Nineteen of the multi-MPO areas are contained within a single State. SIPS in these areas also have variation in how budgets are established. In eight of these areas, a single budget for the entire area is established:

In six of these areas (multi-MPO within one state) sub-area budgets are established for each MPO, or some other subset, such as per county. In other words, the State has negotiated allowable emissions for each sub-area, and the SIP specifically identifies the portion of the motor vehicle emissions budget that applies to each sub-area. These areas are:

MPO conformity determinations in these multi-MPO areas are based on separate regional emissions analyses for each sub-area that are tested against the sub-area budgets independently. Therefore, when sub-area budgets are in place, conformity in one sub-area is not entirely dependent on conformity in another sub-area. However, all sub-areas within a single State's portion of a nonattainment or maintenance area must be in conformity in order for any MPO within that State's portion of the nonattainment or maintenance area to make a conformity determination. In other words, if conformity lapses for one MPO with a separate sub-area budget, the other MPOs within that State's portion of the nonattainment or maintenance area will not lapse immediately, but they will be unable to make new conformity determinations until the first MPO once again determines conformity. Attachment B also notes the multi-MPO areas that have sub-area budgets.

The remaining multi-MPO areas within a single state (5) do not currently have budgets in their SIPs. Therefore, conformity is determined using an emissions reduction test. These areas are also noted in Attachment B.

Institutional Arrangements:

A key challenge in multi-MPO nonattainment and maintenance areas is the coordination of the conformity process between MPOs. Two distinct approaches exist for the conformity processes in these areas. One approach is that the State DOT takes the lead in developing the conformity analysis, as is the case in Connecticut where six MPOs are part of the 8-hour ozone nonattainment areas.

The other approach is that the MPOs use interagency consultation to coordinate the conformity analysis, as is the case in the San Joaquin Valley nonattainment area in California, where each of the 8 MPOs within the nonattainment area conducts its own modeling.

Approximately half of these areas have regularly scheduled interagency consultation meetings, with about a quarter of the areas meeting monthly and a quarter of the areas meeting annually. In the other half of the cases, the MPOs indicate that the interagency consultation meetings are held on an as needed basis. Due to the fact that many of these areas have separate or sub-area budgets as discussed above, frequent coordination between the MPOs is not as prevalent. However, in areas where a single budget is used for the entire area, coordination is essential. In most cases, where agreements do not exist or where interagency consultation is not the forum for establishing schedules, the State DOT sets the schedule for transportation planning.

Analysis issues:

Attachment B also notes for each multi-MPO area which agency takes the lead for travel demand modeling and which agency takes the lead for emissions modeling. As the attachment shows, the same agency takes the lead on both travel demand and emissions modeling in most cases although there are some notable exceptions. An exception is North Carolina, where the State DOT takes the lead on travel demand modeling, and the State air agency takes the lead on emissions modeling. Also, in New York State, the MPOs take the lead on travel demand modeling, while the State DOT and the New York State Department of Environmental Conservation work with the MPOs to develop emission model inputs and factors. The New York Metropolitan Transportation Council uses a post-processor with MOVES to develop their emission rate factor tables.

Updated: 06/03/2014
HEP Home Planning Environment Real Estate
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101