Using the detour factor to avoid detours

In the iterations of the dynamic assignment the drivers are encouraged to try out new paths, which contain links or partial routes that have not yet been traveled (Path search finds only the best possible path in each interval). This may lead to useless paths in the path collection. A path is considered useless if it is an obvious detour. An obvious detour is a path that can be generated from another, already known path by replacing a section by a much longer section. For this purpose, Vissim calculates the total length of nodes and turn relations, from the position in the node entrance or node exit where the paths differ to the position in the node entrance or node exit where the paths are the same again.

You can define how much longer the leg must be compared to the original leg to qualify as a useless path. For example, Vissim checks with a detour factor of 2 for all paths, whether they are just copies of other paths, in which a section has been replaced by a section which is more than twice as long.

If two paths only differ within a node where two parallel turn relations are used (one from each path), the detour factor is still not fulfilled, even if the two turn relations differ more in length than the detour factor. The paths must differ in at least one edge between two nodes for the detour to be recognized by the software.

1.  On the Traffic menu, click > Dynamic Assignment > Parameters.

The Dynamic Assignment: Parameters window opens.

2.  Select the Choice tab.

3.  In the Path pre-selection section select Avoid long detours.

4.  Enter the desired value in the field Avoid long detours. The default value is 2.50.

From now the detour factor is taken into account in the iterations. Detours are shown in the Paths list without travel time or volume data (Attributes of paths). If in the Paths list, synchronization is selected, detours are shown in red in the network display.