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Customizing the Model

TRIMMS has been designed to be fully flexible and customizable by the end user. To allow modification of assumption and results, the model permits full customization of the following:

  • Modal Cost Externalities;

  • Travel Demand Function Elasticities; and,

  • User Supplied Final Modal Shares.

In every step of the analysis, the user can modify these three main factors and is encouraged to customize the model to better fit it to the analysis context. Below, each of these factors is discussed in terms of effects and implication on the model results.

Modal Cost Externalities

In the “Base Case Scenario” worksheet, the user can click on the “Modify Model Parameters” button. This opens a window that shows a series of tabs, each allowing modification of the externalities cost parameters as displayed in Figure 10. The cost parameters are measured in actual dollars per passenger-trip units and are split in peak and off-peak values. These can be accessed by clicking on the apposite tabs. Note that by setting the values to zero, the user can override the model for including a given externality in the evaluation process. For example, if the user is interested in just evaluating the health and safety impacts of a given program or strategy, he or she can set the remaining externality cost values equal to zero. The model will then run and evaluate results only considering health and safety impacts to estimate the value of a passenger trip removed.

Throughout this step by step process, the user is allowed to cancel the operation at any time leaving the model unchanged. A final confirmation is also required to modify the model. Once the model is changed, it can always be reverted to its defaults by clicking on the “Model Reset” button.

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