Long Range Transportation Plan, East-West Gateway is responsible for the preparation of
an air quality conformity determination. Under the provisions of the Clean Air Act Amendments (CAAA) of 1990, East-West Gateway, as the designated Metropolitan Planning Organization
(MPO) for the St. Louis region, is responsible for making the conformity determination. In accordance with the CAAA and
related Federal regulations, both the Transportation Plan and the TIP must be found to be in conformity with all applicable state
implementation plans (SIPs) and with the mobile source emissions budgets as established by the states before the TIP/Long Range Plan can be approved by the MPO and the Federal
To accomplish conformity determination, a series of computer modeling exercises calculate
vehicle emissions from the proposed St. Louis transportation system as compared to motor vehicle emissions levels set by Illinois and Missouri. The pollutants of concern are volatile
organic compounds, oxides of nitrogen and fine particles. These pollutants are found in car and truck exhaust and form ozone and fine particle (PM2.5) pollution.
This process is performed with input from the Air Quality Advisory Committee and the Inter
Agency Consultation Group (IACG). The IACG is a peer group consisting of representatives from East-West Gateway and federal, state and local air and transportation agencies. The IACG
oversees the Conformity Determination process and reaches consensus on planning assumptions, analysis years, tests to be performed and motor vehicle emissions budgets (thresholds).
Inter Agency Consultation Group
The conformity determination is made for the entire 2008 eight-hour ozone non-attainment
area and 1997 PM 2.5 non-attainment area. Ozone non-attainment counties include: Franklin, Jefferson, St. Charles and St. Louis Counties and the City of St. Louis in Missouri; and
Madison, Monroe, and St. Clair counties in Illinois. Jersey County is a maintenance area for the 1997 ozone standard. The annual PM2.5 non-attainment area consists of: Franklin,
Jefferson, St. Charles and St. Louis Counties and the City of St. Louis in Missouri; and Madison, Monroe and St. Clair Counties and Baldwin Township in Randolph County, in Illinois.
As part of the Regional Emissions Analysis two tests are performed. The first test measures
VOCs and NOx emissions based on the 2008 eight-hour ozone National Ambient Air Quality Standard. The anticipated emissions of VOC and NOx which are expected to result from the
implementation of the TIP and Plan in the selected analysis years (the "Action" scenario) has to be shown to be less than the motor vehicle emissions budgets developed by Missouri and
The second test measures fine particle emissions against the 1997 fine particle (PM2.5)
National Ambient Air Quality Standard. The anticipated emissions of direct PM2.5 (exhaust, brake and tire wear) and NOx (a pollutant which can contribute to PM2.5 formation) which are
expected to result from the implementation of the TIP and Plan in the selected analysis years (the "Action" scenario) has to be shown to be less than the total 2002 motor vehicle
emissions inventory for Missouri and Illinois.
Another component of a Conformity Determination is an assessment of progress in
implementing Transportation Control Measures (TCMs) identified in the respective SIPs. These measures are intended to reduce emissions or concentrations of pollutants from transportation
sources by reducing vehicle use or otherwise reducing vehicle emissions. As part of the Conformity Determination, EWGCOG has to certify that TCMs in the categories included in
the SIPs which are eligible for federal funding are on schedule for implementation and that no federal funds are being diverted which might delay their timely implementation.
The Transportation Control Measures Completion Report FY 1998-2000 documents that
the TCMs identified in the states respective one-hour ozone SIPs have been implemented.
Air Quality Conformity Determination currently in effect:
The Board of Directors approved this conformity determination at its August 31, 2016, meeting.