Appendix C, Exhibit 4 

Demographic Data 

Used to Develop Motor Vehicle Emissions Budgets for the 

Atlanta Attainment Demonstrations 

ARC periodically revises its population and employment forecasts based on best 

available current information. Each revision is a two-step process. First, new region-level 

forecasts are produced. These then become region-level controls for census tract and 

traffic analysis zone (TAZ) forecasts. 

The most current region-level control forecasts were completed in 2006. The 

accompanying table summarizes the new population and employment controls for the 

enlarged, 20-county study area. 

ARC staff were assisted in the development of these forecasts by a Technical Advisory 

Committee of local experts on the Atlanta Regional Economy. Chair of the Committee 

was Donald Ratajczak, Professor Emeritus, Georgia State University, and former Chair of 

the GSU Economic Forecasting Center. The committee recommended the final forecasts 

for use by the Commission. 

The second step in the forecasting process uses mathematical models to disaggregate the 

region-level control forecasts to the census tract and TAZ level. TAZs are subdivisions of 

census tracts. 

The DRAM/EMPAL models used to disaggregate the regional controls are iterative over 

a 5-year time period. Starting with the 2000 base, each successive 5-year forecast 

becomes the base for the next. First, the Cube/TP+ model analyzes base year traffic 

patterns and produces accessibility measures within the 20-county forecast area. Then, 

the DRAM/EMPAL models use that accessibility measure plus information on base-year 

population, employment and land use distributions to develop tract-level forecasts of 

those variables five years in the future. A Zonal Allocation Procedure is then used to split 

each tract-level forecast into the TAZs. These TAZ forecasts then become the input used 

by the Cube/TP+ model to produce the accessibility measures that drive the next 

iteration. 

All these models are carefully calibrated based on the best and most current data 

available. Data used in the current effort include 2000 United States Census results, ARC 

estimates of employment by industry for tracts and TAZs, national forecasts of 

employment and population produced by Economy.Com, employment estimates and 

forecasts produced by the Georgia Department of Labor, results of ARC travel surveys 

including the SMARTRAQ household travel survey, transit on-board survey, Hartsfield 

air passenger survey, travel time studies, speed studies, and others. Highway projects and 

the schedule for their completion (primary inputs to the Cube/TP+ model) are developed 

as part of an extensive discussion between ARC staff, local planners, Georgia 

Department of Transportation and various federal agencies. 
C4-2 

The expansion of the study-area from 13 to 20 counties required extensive effort to 

develop the modeling database for the 7 new counties. This expansion was expected, so 

in 2001 ARC produced year 2000 employment estimates by census tract for 12 

nonmember counties in addition to those for its 10 member counties. Land-use data for 

the additional counties was produced using aerial photography taken in 2000. Population 

data for these counties were compiled from 2000 Census results. ARC’s Cube/TP+ travel 

demand model was expanded to cover the new study area and was used to produce the 

year 2000 travel-cost estimates required to calibrate these models. 

ARC also produced tract-level 2005 estimates of population and employment for the 20-

county study area. These estimates supplemented the first iteration of the 

DRAM/EMPAL model. Development of the 2005 estimates and of the year 2000 

calibration database for the non-member counties was coordinated with the affected 

county governments and the Regional Development Centers of which they are members. 

Adjustments are made to the ARC forecasts to account for expected changes that would 

not be apparent from historical data. Some, like expected construction of a new highway 

or the restriction of development in a watershed area, are accounted for directly in the 

models. Others such as the completion of a major development project (Atlantic Station, 

for example) are incorporated as adjustments to the model output. 

The forecasts were used as part of the Envision6 RTP/FY 2008-2013 TIP, adopted by the 

ARC Board on September 26, 2007. 
C4-3 
C4-4 

 20-County Regional Control Forecasts 

Year Total Population Total Employment

1990 3,054,230 1,954,801

1995 3,575,441 2,295,762

2000 4,228,400 2,800,657

2005 4,791,000 2,920,855

2010 5,095,900 3,231,882

2015 5,499,600 3,601,467

2020 5,923,800 3,986,191

2025 6,382,800 4,406,078

2030 6,972,200 4,887,617

2035 7,698,700 5,322,247

Notes: 

1. Population for 1990 and 2000 are U. S Census counts. Population for 1995 and 

2005 are estimates produced by the Atlanta Regional Commission. 

2. Employment for 1990, 1995 and 2000 are estimates by the U. S. Bureau of 

Economic Analysis. 

3. The employment shown in this table will differ from that in the small area 

forecasts because this series includes proprietors. Small area data on proprietors is 

not available.