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Federal Air Quality Transportation Commitments

alt tag hereAir quality is a concern in many metropolitan areas across the country. The Environmental Protection Agency (EPA) has designated the North Central Texas region as a nonattainment area for the pollutant ozone. Vehicle emissions are a major contributor to ozone formation due to the presence of two key “precursors,” or ingredients, to ozone formation in automobile emissions: nitrous oxides (NOx) and volatile organic compounds (VOCs). Despite improvements in technology that lead to cleaner-burning vehicles, the volume of traffic on our highways today continues to produce a significant amount of pollution that contributes to ozone formation.

The North Central Texas Council of Governments (NCTCOG) – Regional Transportation Council (RTC) funds millions of dollars every year to implement projects, programs, and policies to reduce vehicles emissions that create ozone and improve the quality of life in the region. Many of these projects and programs are included in the State’s air quality plan, which is known as the State Implementation Plan (SIP). The SIP demonstrates how and when the nonattainment area will reach attainment of the National Ambient Air Quality Standard (NAAQS). The projects and programs listed in the SIP become federal air quality commitments, thereby making them legally binding commitments at the federal level. If any federal air quality commitment, also known as Transportation Control Measures (TCMs), cannot be implemented in the region by the attainment date specified in the SIP, then that commitment becomes invalid and will require substitution. Under the Texas Administrative Code, a metropolitan planning organization such as the NCTCOG may substitute these invalid TCMs with another project or program with equal or greater air quality benefit.

Over time, the State of Texas revises the SIP for various reasons, thus creating SIP revisions. Three separate SIP revisions have been written for the Dallas-Fort Worth area to address the one-hour ozone standard (this standard was revoked in 2005 due to adoption of the 8-hour ozone standard). Under the one-hour ozone standard, four counties were included in the nonattainment area: Collin, Dallas, Denton, and Tarrant Counties. Only programs and projects implemented within these four counties were eligible as TCMs for these SIP revisions. The following links outline the TCMs contained in each of these three SIP revisions in detail.

Attainment Demonstration SIP (Year 2007)

1999 Rate-of-Progress SIP (9%)

1996 Rate-of-Progress SIP (15%)

The recent adoption of the 8-hour ozone standard necessitates the development of a new SIP revision designed to bring the nonattainment area into compliance with the new standard. Under the 8-hour ozone standard, nine North Central Texas area counties are included in the nonattainment area: Collin, Dallas, Denton, Ellis, Johnson, Kaufman, Parker, Rockwall, and Tarrant. The new SIP revision will thus include projects and programs implemented in all nine counties. NCTCOG staff is currently participating in the development of the 8-hour SIP revision, with an attainment year of 2009.

8-Hour SIP Development

Any questions or comments regarding this information may be directed to Lori Pampell, Transportation Planner, at 817-695-9232 or by email at

1/18/2018   CG %Arc

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