Federal Air Quality Requirements

Transportation Conformity

Transportation Conformity is a federal requirement in nonattainment areas to conduct air quality analysis on projects, programs, and policies identified in transportation plans, transportation improvement programs, federally funded projects, or projects requiring federal approval.  Conformity determinations must demonstrate consistency between emissions expected from the implementation of the long-range transportation plan and Motor Vehicle Emission Budgets (MVEBs) in the applicable State Implementation Plan (SIP).  To meet this criterion, conformity determinations in nonattainment areas with adequate MVEBs from an applicable SIP, must perform a MVEB test.  For the MVEB test, the emissions analysis must demonstrate the estimated emissions are less than the MVEBs in the applicable implementation plan.

The determination of the analysis is a two-step process in metropolitan areas.  The first step is for the Metropolitan Planning Organization (MPO) to make the initial transportation conformity determination at the local level.  For the North Central Texas nonattainment area, this responsibility falls with the Regional Transportation Council (RTC), the MPO’s policy body.  The second step is for the Federal Highway Administration (FHWA) and Federal Transit Administration (FTA) to make a joint transportation conformity determination at the federal level.  Upon favorable federal approval, a four-year window begins during which projects, programs, and policies identified in the Metropolitan Transportation Plan and Transportation Improvement Program may move toward implementation.


2022 Transportation Conformity NEW
Previous Transportation Conformity Determinations
DFW Nonattainment Area Conformity Milestones
Transportation Conformity: A Basic Guide for State & Local Officials
Federal Highway Administration
Environmental Protection Agency

State Implementation Plan

The Federal Clean Air Act (CAA) requires states with areas failing to meet the National Ambient Air Quality Standards (NAAQS) prescribed for criteria pollutants to develop a State Implementation Plan (SIP). The SIP describes how the state will reduce and maintain air pollution emissions in order to comply with the federal standards. Important components of a SIP include emission inventories, motor vehicle emission budgets, and control strategies, including federal, state, and local initiatives.

The Texas Commission on Environmental Quality (TCEQ) develops the Texas SIP for submittal to the US Environmental Protection Agency (EPA). One SIP is created for each state, but portions of the plan are specifically written to address each of the nonattainment areas (e.g. Dallas-Fort Worth (DFW) SIP). The original document for Texas was approved in May 1972, with the most recent revision completed in 2016.

As changes are needed, the SIP is revised rather than rewritten in its entirety. Revisions are often prompted by new federal or state regulations, new modeling techniques, a change in an area’s attainment status, or a change in a nonattainment area's classification. The SIP addresses emissions from on, off and non-road mobile, area, and point sources. The North Central Texas Council of Governments (NCTCOG) completes the on-road emissions inventory to be included in TCEQ's SIP revisions submitted to the EPA. NCTCOG's emissions inventory includes MVEBs, which identify the allowable on-road emission levels to attain the current ozone NAAQS. The MVEBs identified in the SIP will be used in the transportation conformity process to cap the emissions allowed by on-road motor vehicles for the planned transportation network.

Use the following links to explore various aspects of the SIP:

SIP Milestones:  1-hour Ozone NAAQS
SIP Milestones:  8-hour Ozone NAAQS
SIP Control Strategies
TCEQ SIP Revisions
TCEQ SIP Hot Topics
TCEQ - Dallas-Fort Worth: Latest Ozone Planning Activities
TCEQ On-road Mobile Source Emission Control Strategies

Related Committees:

North Texas Clean Air Steering Committee
Air Quality Technical Committee