Controlling iterations of the simulation
For the calculation of the dynamic assignment, the modeled network is simulated again.
Saving data in the path file and cost file
During the iterations, information regarding paths in the network and travel times at the edges in the network is collected. This information is saved in the following files:
- Path file *.weg
- Cost file *.bew
These files represent the current state of the assignment. The names of these files can be entered (Attributes for the trip chain file, matrices, path file and cost file). Thereby you can save the different states of the assignment.
Not saving data in the path file and cost file
You can deactivate the output of evaluations and paths during the simulation. This makes sense, for example, when the assignment is converged and the path selection should no longer be changed for the following simulations.
1. On the Traffic menu, click > Dynamic Assignment > Parameters.
The Dynamic Assignment: Parameters window opens.
2. Select the Files tab.
3. Deactivate the options Store costs and Store paths (and volumes).
Preventing unrealistic congestion of paths
During iteration, the number of known paths increases. In the first iterations, only a small number of paths are available for each origin-destination relation. This can lead to unrealistic congestion of these paths because the traffic demand cannot be distributed to enough paths. These congestion jams disappear again in the following iterations when more paths are found. Due to exponential smoothing of the travel times, the congestion jams continue to have an effect on some of the iterations, slowing down the convergence of the processes.
In order to prevent these initial congestion jams, it may be necessary in the first iteration to send only a part of the demand to the network. The traffic volume can increase with every iteration until the entire demand is allocated. For the modeling of this procedure, Vissim offers a global scale of all specified demand matrices.
1. On the Traffic menu, click > Dynamic Assignment > Parameters.
The Dynamic Assignment: Parameters window opens.
2. Select the Files tab.
3. Enter the desired value in the field Scale total volume to.
