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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 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.

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:

Due to multiple pollutants and standards, the complex area lists are further subdivided by pollutant and standard as follows:

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. Also, many areas around the country fall into two or more of the above categories. For example, the Washington, DC-MD-VA 8-hour ozone nonattainment area encompasses portions of three States (counting the District of Columbia as a State), includes one MPO (the National Capitol Transportation Planning Board), and contains a donut area.

Updated: 06/06/2014
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