Dynamic, Integrated Model System: Jacksonville-Area Application (2013) / Chapter Skim
Currently Skimming:
Pages 119-133
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 119... ...
119 C h A P T e r 4 Model Implementation Demand Model Data Development The proposed model system comprises three primary components: DaySim, the TRANSIMS Router and Microsimulator, and MOVES. DaySim is a travel demand forecast model that predicts household and person travel choices at a parcel level on a minute-by-minute basis.
|
From page 120... ...
120 units because these units are prone to being undercounted in tax assessor databases. EmploymEnt Data Employment data are not usually available at a parcel-level and must instead be developed using address-based business establishment employment information.
|
From page 121... ...
121 blocks or TAZs. Use of these larger spatial units typically reduces the data preparation burden significantly but also limits the sensitivity of the model system.
|
From page 122... ...
122 time required to implement the model. (The project team did have to make relatively crude updates to the employment data in one of the counties.)
|
From page 123... ...
123 changing is one of the primary reasons for congestion and lost vehicles, lane discontinuity errors are extremely problematic. Lost vehicles refers to vehicles that are unable to complete their assignment paths and get "stuck" in the simulation for more than a user-specified number of minutes.
|
From page 124... ...
124 Information Exchange DaySim provides trip and vehicle information to the TRANSIMS Router to perform network assignment. For the Jacksonville region, this process takes approximately an hour of computer processing time.
|
From page 125... ...
125 required to achieve a converged result. The project team developed both typical measures, such as network link-based relative-gap measures, and new measures, such as person-trip– based-gap measures.
|
From page 126... ...
126 were necessary to ensure sufficiently converged assignments within reasonable runtimes. Schedule consistency was identified as another measure of the soundness of a model solution.
|
From page 127... ...
127 Hardware Requirements The model system can be run on computers using either Windows or Linux operating systems. Runtimes for the model system are influenced by a number of factors: • The computing resources available to run the simulation (such as the number of processors, amount of memory available, and speed of storage drive input/output)
|
From page 128... ...
128 Challenges The challenges in interacting with the model are primarily associated with debugging the model system. As has been repeatedly mentioned, the network simulation model is very sensitive to small-scale network coding and parameter assumptions, and the network simulation is subject to frequent failures as input assumptions are being refined.
|
From page 129... ...
129 Because the Jacksonville DaySim implementation was transferred from Sacramento, and the model coefficients and alternative-specific constants were initially estimated and calibrated for the Sacramento region, the project team had to recalibrate the core model components to reflect Jacksonville region- specific travel patterns. Calibration and validation of the entire model system was a highly iterative process that involved making changes to individual model components to better match observed data and evaluating the impacts of those changes on other model components and on overall model system performance.
|
From page 130... ...
130 Microsimulator-based skims are based on the composite speeds of vehicles in the simulation, at that same temporal resolution. These differences and their implications for model calibration and application warrant further exploration.
|
From page 131... ...
131 by the current state-of-the-practice travel-forecasting models, so the integrated modeling tool developed for this project seeks to improve how these policies are addressed. To assess the increased sensitivity of the integrated model system, a set of tests were designed, implemented and evaluated.
|
From page 132... ...
132 assuming that an effective policy is in place. The model results were consistent with expectations based on the structure and linkages of the DaySim and TRANSIMS models.
|
From page 133... ...
133 text files that can be easily processed. Similarly, the travel demand outputs of the model system are also easily interpretable, mirroring the structure of a typical household travel survey.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.