3.14 Feedback - Revision history

Bpaul at 01:41, 13 March 2023

2023-03-13T01:41:12Z

Bpaul at 01:40, 13 March 2023

2023-03-13T01:40:18Z

Bpaul: Created page with "Category:3.0 Model Design Feedback is used in two primary ways in the NERPM activity-based model system: between iterations within the highway assignment process, and bet..."

2023-03-11T01:11:47Z

Created page with "Category:3.0 Model Design Feedback is used in two primary ways in the NERPM activity-based model system: between iterations within the highway assignment process, and bet..."

New page

[[Category:3.0 Model Design]]

Feedback is used in two primary ways in the NERPM activity-based model system: between iterations within the highway assignment process, and between “system” iterations of the model system in which both the Daysim activity-based demand components and the Cube Voyager-based network supply components are executed.

The Method of Successive Averages (MSA) method is a common means of achieving overall stable model system results. The basic idea of the MSA method is to combine the link flows from the current system iteration with the best estimate of link flows from prior system iterations to produce the current best estimate of link flows. This is then used to compute congested link travel times using the volume delay function and these congested times are input to the skimming procedure.

Feedback during “system” iterations in the model is achieved using network skims. It has been mentioned earlier that the skims from the current iteration of the model are used in the next iteration. . In order to facilitate efficient system convergence, the model system is set up to average the highway skims from the current iteration with the skims from the previous iterations. The skims that are used in an iteration after the first iteration are an average of skims at the beginning and end of the previous iteration. For the first iteration of the mode, free flow skims are used. For the second iteration of the model, skim values used are an average of those at the beginning (free flow skims) and at the end (congested skims) of the first iteration. This goes on during subsequent iterations. Currently, three such iterations of the model are run. As noted in the transit skimming section, transit times are function of the highway times and so transit skims are also fed back from one iteration to the other.

@@ Line 5: / Line 5: @@
 The Method of Successive Averages (MSA) method is a common means of achieving overall stable model system results. The basic idea of the MSA method is to combine the link flows from the current system iteration with the best estimate of link flows from prior system iterations to produce the current best estimate of link flows. This is then used to compute congested link travel times using the volume delay function and these congested times are input to the skimming procedure.
-Feedback during “system” iterations in the model is achieved using network skims. The skims generated from the MSA averaged link flows and resulting congested times are used for the auxiliary models and DaySim in the next iteration. Transit skims are updated based on congested link time for the next iteration. Currently, the model is set up to run up to 7 such iterations. At the end of each iteration, the overall model convergence is checked. The model run is terminated if convergence is achieved before 7 iterations. The convergence is achieved when all of the following conditions are satisfied:
+Feedback during “system” iterations in the model is achieved using network skims. The skims generated from the MSA averaged link flows and resulting congested times are used for the auxiliary models and DaySim in the next iteration. Transit skims are updated based on congested link time for the next iteration. Currently, the model is set up to run up to 7 such iterations. At the end of each iteration, the overall model convergence is checked. The model run is terminated if convergence is achieved before 7 iterations. The convergence is achieved when all of the following conditions are satisfied between the current and previous iteration outputs:
 * The % change in Vehicle Miles Travelled (VMT) is less than 5% for both AM and PM periods
 * The % of links with under 5% change in link volumes is less than 5% for both AM and PM periods

@@ Line 1: / Line 1: @@
 [[Category:3.0 Model Design]]
-Feedback is used in two primary ways in the NERPM activity-based model system: between iterations within the highway assignment process, and between “system” iterations of the model system in which both the Daysim activity-based demand components and the Cube Voyager-based network supply components are executed.
+Feedback is used in two primary ways in the NERPM activity-based model system: between iterations within the highway assignment process, and between “system” iterations of the model system in which both the Daysim activity-based demand components and the Visum-based network supply components are executed.
 The Method of Successive Averages (MSA) method is a common means of achieving overall stable model system results. The basic idea of the MSA method is to combine the link flows from the current system iteration with the best estimate of link flows from prior system iterations to produce the current best estimate of link flows. This is then used to compute congested link travel times using the volume delay function and these congested times are input to the skimming procedure.
-Feedback during “system” iterations in the model is achieved using network skims. It has been mentioned earlier that the skims from the current iteration of the model are used in the next iteration. . In order to facilitate efficient system convergence, the model system is set up to average the highway skims from the current iteration with the skims from the previous iterations. The skims that are used in an iteration after the first iteration are an average of skims at the beginning and end of the previous iteration. For the first iteration of the mode, free flow skims are used. For the second iteration of the model, skim values used are an average of those at the beginning (free flow skims) and at the end (congested skims) of the first iteration. This goes on during subsequent iterations. Currently, three such iterations of the model are run. As noted in the transit skimming section, transit times are function of the highway times and so transit skims are also fed back from one iteration to the other.
+Feedback during “system” iterations in the model is achieved using network skims. The skims generated from the MSA averaged link flows and resulting congested times are used for the auxiliary models and DaySim in the next iteration. Transit skims are updated based on congested link time for the next iteration. Currently, the model is set up to run up to 7 such iterations. At the end of each iteration, the overall model convergence is checked. The model run is terminated if convergence is achieved before 7 iterations. The convergence is achieved when all of the following conditions are satisfied: