Integrated Land-Use, Transportation and Environmental Modeling: Validation Case Studies

Abstract

For decades the transportation-planning research community has acknowledged the interactions between the evolution of our transportation systems and our land-use, and the need to unify the practices of land-use forecasting and travel-demand modeling (TDM). Recognizing this interaction, TDMs are linked to land-use models to provide for an integrated land-use/transportation modeling environment. The construction of any modeling framework comes at a cost to its owner. Travel-demand and land-use models require, initially: specification/estimation of the model for a base-year, and calibration of the model with known base-year data; and, on an ongoing basis: improvement of model function (“training”) with improved coefficients, and checking of model results frequently for errors in consistency. Most travel-demand or land-use models are never considered factually “complete”, as the update/correction process is ongoing, due to the model complexity and the vast number of inputs, controls, coefficients, and outputs. So the critical factor in the decision to construct a model or augment an existing model is monetary cost or the level of effort required to do so. The relevant question becomes, first, “What will be the value added by this new cost?” and, second, “Does this added value justify the expenditure of effort?” This project sets out to initiate an analysis of the added validation-accuracy provided by the level of effort required to develop increasingly complex and increasingly disaggregate land-use and travel-demand models. This study examines the forecast output from a range of contemporary model integrations to assess how accuracy has been added relative to the effort required to develop the integrations.

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