TPB News

Updated "Cooperative Forecasts" Will Feed Analyses of 2015 CLRP Update

Mar 9, 2015

Before the Transportation Planning Board votes later this year to approve an annual update to the region's Constrained Long-Range Transportation Plan (CLRP), including six major additions and changes, it will conduct two detailed analyses, one that forecasts future changes in travel patterns under the proposed update, and another that quantifies the air quality impacts of those changes.

The analyses will rely heavily on recent updates to regional population and job growth forecasts developed by the Metropolitan Washington Council of Governments (COG) in close consultation with the local planning departments of its member jurisdictions.

Those forecasts, known as the Round 8.4 Cooperative Forecasts, spell out how much total growth is expected in the region through 2040, as well as where that growth is expected to occur. The forecasts are informed largely by existing or anticipated residential and commercial construction permits, and by longer-term aspirations reflected in locally adopted comprehensive plans.

Use of Round 8.4 Cooperative Forecasts


In all, the latest forecasts anticipate a 26% increase in the region's population over the next 25 years, and a 36% increase in the total number of jobs. The fastest growth is expected to occur in the region’s outer suburban jurisdictions, including Loudoun, Prince William, Frederick, and Charles counties, while the greatest absolute growth is expected in the inner suburban jurisdictions, including Montgomery, Fairfax, and Prince George's counties.

The latest update includes revisions to population and job growth forecasts for Arlington and Prince William counties and the City of Alexandria, and to population forecasts for Fairfax County. The biggest changes were downward revisions of employment forecasts in Arlington and population forecasts in Prince William County.

The newly revised Round 8.4 Cooperative Forecasts will be a key input to analyzing future travel patterns and air quality impacts under this year's proposed CLRP update.

With the aid of a sophisticated computer model, the TPB will use the growth forecasts along with the planned transportation system spelled out in the CLRP to predict where, when, and how people will travel around the region in coming decades. The TPB will summarize the model's predictions in the annual CLRP Performance Analysis.

> Read more about the most recent CLRP Performance Analysis

Then, using the changes in travel patterns that are anticipated over the next 25 years, the TPB will forecast future vehicle-related emissions of four key air pollutants regulated by the federal government. In addition to changes in travel patterns, the emissions forecasts take into account how new vehicle technologies, like on-board emissions controls, more efficient energy systems, and cleaner-burning fuels, are expected to evolve, and how quickly those changes are expected to occur.

The region must demonstrate through the Air Quality Conformity Analysis that future emissions under the CLRP will remain below regional limits known as "emissions budgets."

Both the Performance Analysis and the Air Quality Conformity Analysis are meant to provide decision-makers and the public with information about how well the transportation investments that are currently planned and funded will meet the region's future transportation needs.

The results of this year's analyses will be available for review and comment by the TPB, its stakeholders, and the public for 30 days before the TPB votes to approve the 2015 CLRP update on October 21.

For more information about the 2015 CLRP update, go to

For more information about COG's Cooperative Forecasting process, go to

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