Performing an alternative path search
You can search via the following functions according to Alternative Path Search:
- Stochastic edge evaluation with maximum dispersion share for each OD relation between all zones and the number of passes
- Shortest path price increase for paths from zones, which you select
- Shortest path price increase for paths from dynamic routing decisions, which you select
Multiple passes of the shortest path algorithm with only slightly modified edge evaluations increase the probability of finding more Alternative Paths. These may have higher total costs than the best path, however, they should still be used.
Stochastic edge evaluation with maximum dispersion share
1. On the Traffic menu, click > Dynamic Assignment > Parameters.
The Dynamic Assignment: Parameters window opens.
2. Select the Search tab.
3. Select Search alternative paths.
4. Click the Alternative path search button.
The Alternative path search window opens.
5. Make the desired changes:
| Element | Description |
|---|---|
| Search alternative paths with stochastic edge penalization |
|
| Spread | Dispersion share for each OD relation between zones |
| Passes | Number of the stochastic passes |
If the option is selected, the specified number from stochastic passes is carried out at the beginning of an evaluation interval of the dynamic assignment after each normal shortest path search. Before each pass, the calculation of each edge in the network is multiplied by a random factor between (1-x) and (1+x). x is the maximum dispersion share for each OD relation between zones, which you have entered into the 6. Confirm with OK.
Penalization of the shortest path per zone/OD pair
Vissim runs according to the normal shortest path search as long as additional passes with altered edge evaluations are running until a new path without a route closure is found or the specified maximum number of passes is reached (Influencing path search and path choice).
Thereby before each pass, the evaluations for all edges of the currently best path are multiplied with the edge cost penalization factor (EdgCostPenFact).
1. On the Traffic menu, click > Dynamic Assignment > Parameters.
The Dynamic Assignment: Parameters window opens.
2. Select the Search tab.
3. Select Search alternative paths.
4. Click the Alternative path search button.
The Alternative path search window opens.
5. In the Penalization of the shortest path per zone/OD pair section, right-click the row header.
6. On the shortcut menu, click Add.
The list of attributes opens.
7. Make the desired changes:
| Element | Description |
|---|---|
| FromZone | From zone: Number of the origin zone |
| ToZone | To zone: Number of the destination zone |
| EdgeCostPenFact | Edge cost penalization factor |
| MaxNumPass | Maximum number of passes: Maximum number of stochastic passes |
8. Confirm with OK.
Penalization of the shortest path per dynamic routing decision/OD pair
To use this function, you must have inserted dynamic routing decisions into the Vissim network (Defining dynamic routing decisions). Vissim runs according to the normal shortest path search as long as additional passes with altered edge evaluations are running until a new path without a route closure is found or the specified maximum number of passes is reached (Influencing path search and path choice).
Before each search, the evaluation of each edge of the currently best path is multiplied with the value of the attribute Edge costs evaluation factor.
1. On the Traffic menu, click > Dynamic Assignment > Parameters.
The Dynamic Assignment: Parameters window opens.
2. Select the Search tab.
3. Select Search alternative paths.
4. Click the Alternative path search button.
The Alternative path search window opens.
5. In the Penalization of the shortest path per dynamic routing decision/OD pair section, right-click the row header.
6. On the shortcut menu, click Add.
The list of attributes opens.
7. Make the desired changes:
| Element | Description |
|---|---|
| FromRoutingDecision | From routing decision: Number of the origin routing decision |
| ToZone | To zone: Number of the destination zone |
| EdgeCostPenFact | Edge cost penalization factor |
| MaxNumPass | Maximum number of passes: Maximum number of stochastic passes |
8. Confirm with OK.
Superordinate topic:
