The E - Gas modeling system is a forecast model used to predict National and regional economic activity in order to estimate attainment of ozone and photochemical air quality standards. Since growth in source emissions largely depends on the amount of economic activity growth in an area, a consistent set of growth factors requires forecasts using consistent Gross National Product (GNP) forecasts and a consistent methodology for estimating economic activity in Urban Airshed Model (UAM) and Regional Oxidant Model (ROM) modeling regions. The need for consistent economic growth facts, however, must be satisfied in a way that allows States to use their own estimates of National and regional economic activity. The Economic Growth Analysis System (E-GAS) is an economic and activity forecast model which satisfies both of these standards. The E-GAS modeling system contains three tiers. The first tier includes available national economic forecasts which are used to drive the regional economic models. The second tier includes regional economic models for the UAM modeling areas, as well as the States in the ROM modeling regions. The third tier estimates fuel consumption, physical output, and vehicle miles traveled (VMT) based on the second tier's regional economic forecasts. The tiers must be sequentially executed, since data are created by and passed from early tiers for transfers to later tiers. The three-tiered structure of E-GAS allows users flexibility in modeling. Although a tier must be run before preceding to later tiers, the system allows the models to be rerun at the user's discretion. For example, users may run the National model using either BLS or WEFA forecasts before performing regional modeling on the last national model run. E-GAS is designed such that growth factor projection scenarios for each nonattainment area and attainment portion of States can be made using a common assumption about future U.S. economic activity. The National economic forecasts in E-GAS
can provide a common forecast with which to forecast regional economic growth. The nature of ozone formation requires attention to be paid to the location as well as the level of economic activity. National forecasts provide estimates of total economic activity. The regional model will distribute this activity among U.S. urban areas, States, and regions. The spatial characteristics of the regional forecasts are designed to meet the needs of the photochemical models used by ozone nonattainment areas.