5:52 Please confirm if my interpretation is correct for vehicle volume on edges: For convergence to occur, the volume difference on a particular edge must be within 15 vehicles for consecutive dynamic assignment evaluation periods. For example, if dynamic assignment evaluation time is 900s, and if volume on an edge is 100 vehicles for 0-900s, then for 901-1800s, the volume must be between 85-115 veh in that edge for convergence.
Hi @nafisanwari6288, almost :). That is not between consecutive evaluation periods, that is between consecutive runs. Later in the video, I open the evaluation files and show how it is calculated. You can see evaluation periods are listed there and calculation is made for each separately. The reason for this is 'evaluation periods' are basically representing different traffic conditions, for example different hours (5-6pm and 6-7pm for example), so traffic will be different for these. Convergence is between runs, a sim run is considered converged if it is not 'really different' from the previous run(s). There is also setting in the bottom on the dialog box/tab saying the 'required number of consecutive convergence runs'. This sets how many times this needs to happen to make sure your convergence is stable. I hope my explanation makes sense. Let me know if it does not.
Thanks for the great information. I had a query. At 8:18, why is the evaluation interval greyed out. How can I change the evaluation interval for dynamic assignment?
Hi @nafisanwari6288, it is greyed out when you already have the routing files created (BEW, WEG). If you want to change it, you need to remove the already created files for the assignment. The reason for this is that those files already have the evaluation period set up. If you open the files you can check it. However, please note that this evaluation period is not for the modelling results like node evaluation, data collection, delay... Those can be set up in the main evaluation menu and in the dynamic assignment dialog box. Hope makes sense
@@MatyasLemberTutorials Hello, thanks for the suggestions. Yes, I am able to delete .bew and .weg files now and change dynamic assignment evaluation period. Yes, I can change evaluation period for other results from Evaluation>> Configuration>> Result attributes. The only thing I didn't understand is what you meant in the last line about dynamic assignment dialog box.
@@nafisanwari6288 What I meant was: In the bottom of the convergence criteria dialog box, you can set up the number of consecutive runs checked for convergence. If you set it to for example 4, Vissim checks that the criteria you set remains for 4 consecutive runs. Basically, the results between those 4 runs are stable and they don't change much. Some authorities require this setting to be used. Many times it can be that convergence get lost after 1 run, especially when the network is congested. Hope it makes sense?
Thanks for a great video on DTA ! Can you please explain more about the 'scale to total volume to' in the Dynamic Assignment Parameters vs the 'Dynamic Assignment Volume increment' located in the Simulation Parameters. Can you ramp up Volumes by 10% or a small amount for at least 10 simulation runs to get better path selection if it is a congested network? Additionally do you typically use the Kirchhoff Stochastic assignment? and how different would it be from using the Equilibrium assignment?
Hi, thank you! 'Scale total volume to' basically a factor Vissim will apply to your matrices. So all cells will be factored to this. Let's say to 50%. So 100 vehicles become 50. With this setting, all simulations will be run at 50% of the demand. If you set a percentage in 'Dynamic assignment Volume increment', then this percentage will keep increasing your 'Scale total volume to' figure every simulation run. Let's say you put 10% here. 1st run will be using 50% of the demand. The 2nd will use 60%, 3rd 70%, 4th 80%, 5th 90%, 6th 100%, 7th 100%, 8th 100%...... nth 100% If you set it to 0%, the reduction will remain forever, until you manually change it. This is helpful if your network needs to balance out a lot. If you have a very congested path/route, but there are alternatives. This also helps Vissim to run a few runs quickly (with less traffic, so faster) so you can find more paths quicker. Stochastic (Kirchhoff) is the mainly used option. The Equilibrium option was only introduced from Vissim 9 I think. Not many people use it. Probably because there is no clear guidance or documentation from the developer on pros and cons and no one has time to experiment with it once the project is done. And also everyone just got used to the Kirchhoff one. So yes, go with that. Use the other only in cases when you cannot solve your assignment with Kirchhoff. It would produce different results. But this greatly depend on your model, and the settings for the dynamic assignment.
5:52 Please confirm if my interpretation is correct for vehicle volume on edges: For convergence to occur, the volume difference on a particular edge must be within 15 vehicles for consecutive dynamic assignment evaluation periods. For example, if dynamic assignment evaluation time is 900s, and if volume on an edge is 100 vehicles for 0-900s, then for 901-1800s, the volume must be between 85-115 veh in that edge for convergence.
Hi @nafisanwari6288, almost :). That is not between consecutive evaluation periods, that is between consecutive runs. Later in the video, I open the evaluation files and show how it is calculated. You can see evaluation periods are listed there and calculation is made for each separately. The reason for this is 'evaluation periods' are basically representing different traffic conditions, for example different hours (5-6pm and 6-7pm for example), so traffic will be different for these. Convergence is between runs, a sim run is considered converged if it is not 'really different' from the previous run(s).
There is also setting in the bottom on the dialog box/tab saying the 'required number of consecutive convergence runs'. This sets how many times this needs to happen to make sure your convergence is stable. I hope my explanation makes sense. Let me know if it does not.
@@MatyasLemberTutorials I understand now thank you
Thanks for the great information. I had a query. At 8:18, why is the evaluation interval greyed out. How can I change the evaluation interval for dynamic assignment?
Hi @nafisanwari6288, it is greyed out when you already have the routing files created (BEW, WEG). If you want to change it, you need to remove the already created files for the assignment.
The reason for this is that those files already have the evaluation period set up. If you open the files you can check it. However, please note that this evaluation period is not for the modelling results like node evaluation, data collection, delay... Those can be set up in the main evaluation menu and in the dynamic assignment dialog box. Hope makes sense
@@MatyasLemberTutorials Hello, thanks for the suggestions. Yes, I am able to delete .bew and .weg files now and change dynamic assignment evaluation period. Yes, I can change evaluation period for other results from Evaluation>> Configuration>> Result attributes. The only thing I didn't understand is what you meant in the last line about dynamic assignment dialog box.
@@nafisanwari6288 What I meant was: In the bottom of the convergence criteria dialog box, you can set up the number of consecutive runs checked for convergence. If you set it to for example 4, Vissim checks that the criteria you set remains for 4 consecutive runs. Basically, the results between those 4 runs are stable and they don't change much. Some authorities require this setting to be used. Many times it can be that convergence get lost after 1 run, especially when the network is congested. Hope it makes sense?
@@MatyasLemberTutorials Yes I understand, thank you for the explanations.
Thanks for a great video on DTA ! Can you please explain more about the 'scale to total volume to' in the Dynamic Assignment Parameters vs the 'Dynamic Assignment Volume increment' located in the Simulation Parameters. Can you ramp up Volumes by 10% or a small amount for at least 10 simulation runs to get better path selection if it is a congested network? Additionally do you typically use the Kirchhoff Stochastic assignment? and how different would it be from using the Equilibrium assignment?
Hi, thank you!
'Scale total volume to' basically a factor Vissim will apply to your matrices. So all cells will be factored to this. Let's say to 50%. So 100 vehicles become 50. With this setting, all simulations will be run at 50% of the demand.
If you set a percentage in 'Dynamic assignment Volume increment', then this percentage will keep increasing your 'Scale total volume to' figure every simulation run. Let's say you put 10% here.
1st run will be using 50% of the demand. The 2nd will use 60%, 3rd 70%, 4th 80%, 5th 90%, 6th 100%, 7th 100%, 8th 100%...... nth 100%
If you set it to 0%, the reduction will remain forever, until you manually change it.
This is helpful if your network needs to balance out a lot. If you have a very congested path/route, but there are alternatives. This also helps Vissim to run a few runs quickly (with less traffic, so faster) so you can find more paths quicker.
Stochastic (Kirchhoff) is the mainly used option. The Equilibrium option was only introduced from Vissim 9 I think. Not many people use it. Probably because there is no clear guidance or documentation from the developer on pros and cons and no one has time to experiment with it once the project is done. And also everyone just got used to the Kirchhoff one. So yes, go with that. Use the other only in cases when you cannot solve your assignment with Kirchhoff.
It would produce different results. But this greatly depend on your model, and the settings for the dynamic assignment.
@@MatyasLemberTutorials Thank you so much !!