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Dr Paul Van Buskirk and Carleton Ryffel

 A Time to Plan for the Upturn By Dr. Paul Van Buskirk, PE, AICP and Carleton Ryffel, AICP

 Our current economic downturn does not negate the need to plan for the future. Rather it is a “breathing time” for more thoughtful and balanced planning to maximize public and private investment in  infrastructure.  Despite the economic climate, accurate population forecasts by local governments are necessary in order to get the optimal return on public and private investments.

Population projections determine when infrastructure such as roads, utilities, schools, parks, fire stations, commercial centers and industrial parks are needed to meet the demands of the populations.

The underlying key to reliable and efficient short and long range planning for these needs is accurate population forecasting so that infrastructure is neither prematurely advanced nor allowed to fall behind population demand. The cost to “catch up” far exceeds the cost of being proactive to accurately meet the demands as they occur. 

Investing public capital to replace infrastructure before the term of its useful life (i.e. 20 years) due to over-utilization, can result in negative returns on public investment. 

Likewise, over-estimating population could result in large-scale capital investment expenditures that are underutilized with few beneficial returns.

Perhaps this is why the Florida Department of Community Affairs, as part of their Comprehensive Plan amendment reviews, now poses the question of demonstrating the need for  land use changes.

To forecast aggregate growth, there are many more accurate applications and methodologies than the typical linear extrapolation. Unfortunately, typical linear population extrapolation has historically underestimated or overestimated population growth in Florida. Research has demonstrated that for fast growing areas, as our state as a whole has been, the Sigmoid (S-Shaped) Curve is a more accurate representation. If we look at the growth curves of the essentially built out cities of St. Petersburg, Miami and Tampa whose growth histories are over 100 years, they are all sigmoid curves.

An Interactive Growth Model,™ a copyrighted population-driven software program, has been created that can be used to forecast the aggregate and spatial distribution of population, in five-year increments to build-out along with the timing, apportionment, distribution and optimal location of support land uses, both public and private, for that population. For planning purposes, “build-out” is assumed to be 90% of the ultimate population of a study area.

The model has been applied to study areas of various sizes, from 100 square miles up to 1900 square miles, with the latter being an area slightly larger than the State of Delaware. To address the huge amount of data in the model, study areas are disaggregated into subareas, usually Traffic Analysis Zones (TAZs) or Census Block Groups, with each method having their own advantages. Disaggregation provides greater levels of detail, over manageable areas that are then combined into a whole.

This growth model applies a series of algorithms to determine the optimal solution for the location and timing of various land uses. For example, some of the parameters for the algorithms could include the location and timing of development, the proximity of existing development, propensity to aggregate land parcels and the transportation network. The model is also interactive and therefore dynamic because through its software, an element, parameter or standard can be changed to reflect changing times, priorities, policies, zoning or land use. Those changes are then processed through its software and the outputs adjusted and reallocated. It also presents the opportunity to demonstrate alternative “What-if” growth management scenarios valuable to community planning and budgetary purposes, meaning an idea of the potential magnitude of the costs associated with support public facilities, which includes infrastructure. There are also myriad sub-models of the growth model that are of importance to an individual community.

Some of these include commercial land use allocations and commercial  corridors, school plant allocations, industrial parks, parks, recreation and open space, Fire/EMS allocations and locations, etc. Further, the data from the model can be used to update transportation plans, including MPO transportation models, water/sewer master plans, economic development, comprehensive plans, annexation impact analysis and others.

 While no model is perfect, this model is a step in the right direction because it is based on a sound population forecasting methodology. It provides accurate data for updating other plans, is capable of addressing data changes and their outputs efficiently. Finally, it provides valuable input into the decision-making process of governments as related to comprehensive planning and the potential cost of public service alternatives.

 Dr. Paul Van Buskirk, AICP, P.E. and his partner Carleton Ryffel, AICP are principals in the firm of Van Buskirk, Ryffel and Associates, Inc.

 Their firm along with the City of Auburn, Alabama, were awarded the Outstanding Planning  Award, by the Alabama Chapter of the American Planning Association in 2009 for the Auburn Interactive Growth Model. www.interactivegrowthmodel.com