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167523-1 Report Abstract

Uncertainty in Integrated Land Use-Transport Models: Simulation & Propagation

Sriram Krishnamurthy and Kara Kockelman, University of Texas at Austin, September 2002, 29 pp. (167523-1)

This work examines the propagation of uncertainty in outputs of a standard integrated model of transportation and land use. Austin-calibrated DRAM-EMPAL predictions of residence and work locations are used as inputs to a four-step travel demand model (TDM), and the resulting travel times are fed forward into the future period’s land use models. Covariance in inputs (including model parameters and demographic variables) was accommodated through multivariate Monte Carlo sampling of 200 scenarios. Variances in land use and travel predictions were then analyzed, over time, and as a function of input values. Results indicate that output variations were most sensitive to the exponent of the link performance function, the split of trips between peak and off-peak and several trip generation & attraction rates. 20 years in the future, final uncertainty levels (as measured by coefficients of variation) due solely to input and parameter estimation errors are on the order of 38% for total regional peak-period VMT, 45% for peak-period flows, and 50% and 37% for residential and employment densities, respectively.

Keywords: Uncertainty Outputs, Travel Demand Model, Land-Use, Covariance

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