Appendix C, Exhibit 4

Demographic Data Used to Develop Motor Vehicle Emissions Budgets for the

Atlanta Attainment Demonstrations

ARC periodically revises its population a nd employment forecasts based on best
available current information. E ach revision is a two-step proc ess. 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 popul ation 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, Geor gia 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 fore casts to the census tract and TAZ level. TAZs are subdivisions of

census tracts.

The DRAM/EMPAL models used to disaggregat e 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 C ube/TP+ model analyzes base year traffic patterns and produces accessibility measures within the 20-county forecast area. Then,
the DRAM/EMPAL models use that accessibilit y measure plus information on base-year population, employment and land use distributions to develop tract-le vel forecasts of those variables five years in the future. A Z onal 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 accessi bility measures that drive the next
iteration.

All these models are carefully calibrated ba sed 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 Ec onomy.Com, employment estimates and forecasts produced by the Georgia Department of Labor, results of ARC travel surveys including the SMARTRAQ household travel surv ey, transit on-board survey, Hartsfield air passenger survey, travel time studies, sp eed studies, and others. Highway projects and the schedule for their comple tion (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 ne w 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 suppl emented the first iteration of the DRAM/EMPAL model. Development of th e 2005 estimates and of the year 2000
calibration database for the non-member count ies was coordinated with the affected county governments and the Regional Developmen t Centers of which they are members.

Adjustments are made to the ARC forecasts to account for expected changes that would not be apparent from historic al data. Some, like expected construction of a new highway or the restriction of development in a wate rshed area, are accounted for directly in the models. Others such as the completion of a major development proj ect (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.C4-3C4-4 

### 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 Ce nsus 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 propr ietors. Small area data on proprietors is
not available.