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Iteration Threshold Configurations

TDM23 offers three configurations for iteration thresholds: speed feedback iteration, highway assignment iteration, and Park-and-Ride (PnR) iteration. Each configuration allows for specific adjustments to ensure accurate and efficient model runs.

Speed Feedback Iteration

Speed feedback iteration is critical for ensuring that the model accurately reflects traffic conditions by iterating until speeds converge to a stable state. Users can specify the following parameters in the "Primary Inputs | Run Mode" section:

  • Maximum Speed Feedback Iterations: Sets the maximum number of iterations the model will perform to achieve speed feedback convergence.
  • Speed Feedback PRMSE Threshold (%): Defines the percentage threshold for the root mean square error (PRMSE) that indicates convergence on highway link volumn between iterations.

By default, the the feedback loop is configured to run up to 4 iterations to attain a PRMSE threshold of 1%. This configuration ensures that the speed estimates used in the model are stable and reliable.

Highway Assignment Iteration

Highway assignment iteration focuses on the convergence of traffic flow and assignment on the road network. Users can specify the following parameters in the "Supply | Roadway" section:

  • Number of Assignment Iterations: Sets the maximum number of iterations for the highway assignment process.
  • Relative Gap Threshold: Defines the convergence criterion based on the relative gap between successive iterations.

By default, the roadway assignment is configured to run up to 200 iterations to achieve a relative gap threshold of 0.0001. This ensures that the traffic assignment results are stable and accurate.

PnR Iteration

PnR iteration addresses the convergence of shadow costs for Park-and-Ride (PnR) facilities. This is crucial for models that incorporate dynamic shadow costs to reflect changes in parking demand and supply. If Dynamic Shadow Costs are enabled in the "Primary Inputs | Run Mode" section, users can configure the following parameters in the "Supply | Transit" section:

  • Maximum Iterations for PnR Shadow Cost Convergence: Sets the maximum number of iterations allowed for the convergence of PnR shadow costs.
  • Transit PnR Constraint Parameters: These parameters define the constraints and thresholds for PnR convergence.

If the PnR iteration does not converge before reaching the maximum iterations, users may need to adjust the Transit PnR Constraint Parameters to ensure accurate results. By dafault, the maximum iterations for PnR shadow cost convergence is 16.

Model Execution Options

TDM23 offers various options for executing the model in TransCAD UI:

Single Scenario Execution

With one scenario defined and selected, you can run the model for the current scenario by clicking on the Run Model Once icon.

Multiple Scenarios Execution

If multiple scenarios are defined, you can select one of the scenarios and execute the model for multiple scenarios by clicking on the Run Two or More Scenarios icon. You can adjust the execution sequence in the pop-up window.

Step-by-Step Execution

With a specific scenario selected in the model structure, you can right-click on a component to:

  • Run Step: Execute a specific step. If it is not the first component, ensure you provide the necessary files for that step.
  • Run Model from Here: Execute the model starting from the selected step.
  • Run Model to Here: Execute the model up to the selected step.
  • Run Range of Steps: Execute a specified range of steps.

These options provide flexibility in running the model, allowing you to tailor the execution to your specific needs.