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Transportation Conformity Practices in Complex Areas

A key goal of the FHWA is to increase the capacity of MPOs throughout the country in meeting a host of planning requirements, including those related to air quality and transportation conformity. FHWA's Office of Natural and Human Environment recently completed an assessment of how conformity works in certain types of nonattainment and maintenance areas, so-called "complex areas."

The purpose of this study was to further understand how MPOs have been carrying out the transportation conformity requirements in the different types of complex nonattainment and maintenance areas. Specifically, the research was designed to document how conformity determinations and regional emissions analyses are being done in these different types of areas, and to share with other MPOs and conformity stakeholders this information. This information may be particularly valuable in light of nonattainment designations under the new 8-hour ozone and particulate matter standards, which will likely result in additional complex areas. However, it should be noted that the information discussed in this study reflects the current 1-hour ozone standard, and does not include "complex" 8-hour ozone areas.

The metropolitan transportation planning process is designed around the metropolitan planning organization (MPO), the federally designated planning entity for urbanized areas with a population over 50,000. In contrast, the air quality planning process is designed around nonattainment or maintenance area boundaries, which may or may not coincide with MPO planning boundaries.

While the simplest and most straightforward situation is one where the MPO planning boundaries and the nonattainment or maintenance area boundaries coincide, FHWA has identified four types of "complex" areas where this is not the case:

It should be noted that in some cases only a portion of an identified MPO is contained within the subject nonattainment or maintenance area, and vice versa.

In addition, many areas around the country fall into two or more of the above categories. For example, the Washington, DC-MD-VA 1-hour ozone nonattainment area encompasses portions of three States (counting the District of Columbia as a State), includes the planning area of two MPOs (the National Capitol Transportation Planning Board and the Fredericksburg MPO), and contains a donut area.

The approach to this research was to canvass each FHWA Division Office in States where there are complex areas. This website provides a synthesis of information collected. Each of the four categories of complex areas is described separately along with the synthesis of our findings for that category of area:

Updated: 07/06/2011
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