CEE4620 Class Notes

CEE4620 Class Notes - CALINE4 Randall Guensler Microscale...

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CALINE4 Randall Guensler © Guensler Trans/AQ 2002 2 Microscale Modeling Microscale modeling is performed for two reasons – Ensure that a violation of ambient air quality standards will not occur (conformity) – Compare relative impacts of project alternatives on air quality in an Environmental Impact Statement (EIS) under the National Environmental Policy Act (NEPA) • NEPA is more than a demonstration that a health- based standard is not violated • The EIS must compare impacts across alternatives so that the results can be used in decisionmaking
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© Guensler Trans/AQ 2002 3 Microscale Modeling Goals Ensure that future activity on a transportation facility will not lead to a violation of the National ambient air quality standards established by the EPA under the Clean Air Act – Predict future travel demand and traffic volumes on the facility and surrounding facilities of concern – Estimate emissions from vehicles operating on the facilities – Predict downwind concentrations as a result of atmospheric dispersion of the emissions © Guensler Trans/AQ 2002 4 Double Gaussian Distribution Source: (Tesche, 1990)
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© Guensler Trans/AQ 2002 5 Downwind Effects © Guensler Trans/AQ 2002 6 Comparing Alternatives For those projects where a microscale CO analysis is performed, each reasonable alternative should be analyzed for the estimated time of completion and the air quality plan design year A brief summary of the methodologies and assumptions used should be included in the draft EIS Total CO concentrations (project contribution plus estimated background) at identified reasonable receptors for each alternative should be reported FHWA Technical Advisory T 6640.08, 8(b), revised November 27, 1987
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© Guensler Trans/AQ 2002 7 Microscale Impact Assessment Identify project goals and objectives Undertake intersection screening analysis – Small projects may not require modeling Assemble available data Collect field data Estimate peak traffic volumes Obtain applicable emission rates from MOBILE Run dispersion model Compare results to NAAQS Provide results in comparative format for NEPA © Guensler Trans/AQ 2002 8 Transportation Network The modeling run should include the project and all relevant major roadways (included in travel demand modeling) that have an impact on the selected receptors Because CO projections are being made for the future transportation system, substitution of current background concentration data for existing roadways is not sufficient A detailed project map should be prepared for use in developing base model input file
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© Guensler Trans/AQ 2002 9 Downtown Atlanta Marietta Lawrenceville 1995 Spatial Distribution of Atlanta Road Volumes 7-8 AM Bachman 1998 4-Step Model Traffic Volumes © Guensler Trans/AQ 2002 10 Simulation Modeling Options Simulation models employ a coded network and car- following theory to predict traffic volumes as a function of demand volumes, turning movements, and system
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CEE4620 Class Notes - CALINE4 Randall Guensler Microscale...

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