Uncertainty in Integrated Land Use-Transport Models

00938299509569942002PDFResearch PaperSWUTC/02/167223-110727DemographicsForecastingLand use modelsSimulationTraffic assignmentTravel behaviorTravel demandTravel timeUncertaintyUrban transportationUncertaintyIntegrated Land-UseModelingForecastUrban SystemsUrbamSimUnited StatesTexas Transportation InstitutePradhan, AnantKockelman, KaraUniversity of Texas at Austin. Center for Transportation ResearchTexas Transportation InstituteSouthwest Region University Transportation Center (U.S.)US Transportation CollectionThis study examines the impact of uncertainty in the land use component of a partially integrated land use-transportation modeling system called UrbanSim. Outputs from the land use model (LUM) act as inputs for a traditional 4-step travel demand model (TDM), and travel times from the traffic-assignment stage of the TDM are fed forward into the subsequent years LUM. This work examines the propagation of uncertainty across model stages as well as at each model stage over time. A factorized design approach is used to model uncertainty in demographic inputs (which include aggregate growth rates and mobility rates) to the land use model, as well as uncertainty in various model parameters. The results suggest that while several model inputs may affect model outputs in the short run, only those inputs that have a cumulative effect are likely to have a significant impact on outputs in the long run. The results also suggest that uncertainty in model outputs may increase for the first few years for which the model is run, as modified inputs send shocks through the urban system. However, the level of uncertainty appears to come down in later years, as households, jobs, and developers respond to changed input conditions