About Arlington County’s Forecast

Why does Arlington County produce a population and jobs forecast?

Arlington County participates in the Metropolitan Washington Council of Governments (MWCOG) Cooperative Forecasting program – a joint effort with Federal and local governments of the region to produce a consistent set of long-range economic and demographic forecasts. These forecasts are the basis of functional plans in the areas of transportation, water resources, air quality, housing, land use, and energy.

The regional forecast is used in travel demand models that determine how various transportation investments affect mobility in the region. A primary purpose of the model is to determine air quality conformity through the regional air quality analysis as mandated by the federal Clean Air Act Amendments of 1990. Air quality conformity is necessary to receive federal funding for transportation projects.

What is produced in the forecasting process?

Arlington County produces a forecast for four variables: housing units, households, population and employment.

• Housing Unit: A house, an apartment, a mobile home or trailer, a group of rooms, or a single room occupied as separate living quarters, or if vacant, intended for occupancy as separate living quarters. (U.S. Census Bureau)
• Household: A household includes all the people who occupy a housing unit (such as a house or apartment) as their usual place of residence. (U.S. Census Bureau)
• Population: All people, male and female, child and adult, living in a given geographic area. (U.S. Census Bureau)
• Employment: The total number of jobs located in a given geographic area.

How is the forecast produced?

Arlington County’s Population and Employment forecast is produced by the Department of Community Planning, Housing and Development’s Research and Strategic Initiatives Group.

Arlington’s forecasting process is development-based and is informed by the land use policy guidance of Arlington’s General Land Use Plan (GLUP).  The forecast uses two primary sources of development information:

• County-wide development pipeline data on recently completed projects, projects under construction, and approved projects.
• Development assumptions derived from parcels with anticipated growth from approved sector plans and small area plans.

Updates to Arlington County’s forecast are generally produced on an annual or 2-year basis.  Forecasts are produced for a 30-year period, broken down in to 5-year increments.  Each major forecasting process led by MWCOG is call a Round.  In October 2022, Arlington County submitted updated forecast numbers for Round 10.0.

What assumptions are included in the forecast?

The following are assumptions applied to the forecast Round 10.0, which was submitted to MWCOG in October 2022.

• Projects that were completed, under construction, or approved as of July 1, 2022.
• Parcels with anticipated growth from approved plans.
• Areas forecasted for future growth must either have been approved by the County Board through the site plan/special exception or form-based code processes or designated for higher density development in accordance with the relevant GLUP, sector plans, small area plans, and the zoning ordinance as of July 1, 2022.
• The timing of forecasted residential and office development is informed by property ownership patterns, development activity, and plan assumptions. This timing is then further calibrated using historic countywide and submarket residential and office absorption rates.

Population Forecast

• The population estimate method is based on the Master Housing Unit Database, a dataset of all Arlington housing units.
• The estimation method is driven by changes in housing supply and applies vacancy and average household size factors to each existing and forecast housing unit based on housing type (single family and multifamily) and Census Tract. The factors are calculated based on the 2020 ACS 5-Year Estimates at the Census Tract level and held constant throughout the forecast.
  
  

Employment Forecast

 The employment forecast method is based on existing and forecast development, vacancy rates, and average square feet per employee.  CPHD’s Development Tracking Database, a comprehensive dataset of development, contains building square footage by use: office, retail, other, and hotel.

2020 Employment Estimate:

• A December 2020 development snapshot was used to estimate the 2020 jobs located in Arlington. CoStar vacancy data was used to determine an office vacancy rate for each of Arlington’s submarkets (including the non-submarket area) as of 4th Quarter of 2020. These vacancy rates were applied to the Gross Floor Area (GFA) of office space for each sub area. The occupied GFA was divided by 250 sq ft per job to determine the number office jobs.
• Retail jobs were calculated by applying a 6% vacancy rate and 450 sq ft per job.
• Industrial jobs were derived from the other sq ft located in industrial zoned areas and divided by 650 sq ft per job.
• Hotel jobs were calculated as 2 hotel rooms per one job and then distributed to office, retail, and industrial jobs by the following percentages respectively: 20%, 65%, and 15%.
• Other jobs were calculated by dividing the other sq ft by 600 sq ft per job
• MWCOG’s recommended self-employment estimate for Arlington was utilized for the 2020 self-employment jobs estimate. ACS data was used to distribute the self-employment jobs throughout the county in residential areas.

 2025-2050 Employment Estimate:

• An employment base was developed for each of the 5-year increments for the purpose of capturing changing vacancy rates in Arlington’s existing 39.5 million sq ft of office space.  2^nd quarter 2022 CoStar office vacancy rates, at the submarket level (including the non-submarket area), were used to determine the current office vacancy rates and normalized to the 10-year averages by 2050. Incremental office vacancy rates were applied to the existing office space to recalibrate the employment base.  The same assumptions as listed above in the 2020 Employment Estimate bullet were applied for retail, industrial, hotel, and other jobs.
• To this base the net new jobs were added at each of the 5-year increments.
• Vacancy rates for forecasted office space are kept at a constant 10% throughout the forecast.  This is to demonstrate that new office construction will be Class A space and will be occupied at different rates than existing office space.
• For self-employment jobs, the percentage of self-employed jobs to total household population was calculated for 2020.  This percentage was applied to the forecast household population for each forecast year to determine the number of self-employed jobs. ACS data was used to distribute the self-employment jobs throughout the county in residential areas. 

• More details on Arlington Forecast Methods(PDF, 1MB)

Does Arlington project Students?

Yes, Arlington Public Schools projects students. Arlington’s population and forecasting process, managed by CPHD, forecasts population, households, housing units, and employment; it does not forecast students.

What is Arlington’s 4-step forecasting process?

Step 1: Develop Current Year Development Base

• Housing: Master Housing Unit Database
• Employment: Development Tracking

• The General Land Use Plan (GLUP), County Board approved site plans, phased development site plans, sector plans, small area plans, and the zoning ordinance 
  
  

Step 3: Calibration and Timing

• Historic absorptions rates are calculated for multifamily housing units, office square footage and retail square footage.

Step 4: Calculate Population and Employment

• Apply factors: occupancy, average household size, office vacancy rate, space conversion factors

How accurate is Arlington County’s forecast?

Arlington County’s population forecast has proven to be accurate with a low margin of error. Below is a chart that shows the population forecast for 2020 based on the forecast version (Round 7-9).  Between the forecast years of 2005-2021, the forecasts has a relatively low margin of error – an average of 1.8%.  For each of the rounds, the table also lists the percent difference between the actual 2020 Census number reported by the U.S. Census Bureau and the population forecast by the County. Every round the forecast is readjusted to reflect current economic conditions and long term trends.

* Prior to the release of the 2020 Census.

What are the differences among counts, estimates, projections, and forecasts?

• Count: determines a total number (Decennial Census)
• Estimate: calculations of past or present conditions, utilizing counts and known statistics
• Projection: measures future growth by extrapolating current trends and applying statistical techniques
• Forecast: projections, modified by policy, work to resolve trends (past and current) with future policy

Data Sources

• 2010 Decennial Census 
• County Development Information
• General Land Use Plan (GLUP)
• Arlington’s Sector Plans and Small Area Plans
• CoStar