Node control in mesoscopic simulation
In mesoscopic simulation there are some rules for modeling signalized and non signalized intersections that differ from the rules that apply for microscopic simulation. You need to take these rules into account if you manually and individually define meso network nodes in the Network editor, instead of creating all meso network nodes for the entire network at once.
For signalized intersections note that the decisive factors are the stop position and storage capacity. The vehicle always stops at the meso network node. If the real situation cannot be modeled with one meso network node only, model several nodes, e.g. for a channelized right turn. For conflict control at intersections, in mesoscopic simulation, Vissim only looks at the vehicles on the edges that lead into the node.
Signalized intersections
Detectors in the mesoscopic simulation transfer the following data to dynamic controllers:
- The front edge of the vehicle reaches the detector.
- The vehicle is on the detector.
- The rear edge of the vehicle reaches the end of the detector.
- Number of front edges and rear edges
- Vehicle number, vehicle type, vehicle length
- Occupancy
- PT line
If the detector lies within a meso-node upstream of a signal head, the following applies:
- The detector is treated as if it were directly upstream of the signal head.
- The signal head is treated as if it were directly upstream of the node entry.
Fixed type signal control only distinguishes between the statuses stop and drive. The signal state sequences of signal groups either cause vehicles to wait at the entry of the meso network node or enter the node:
- The signal states Red and Red flashing are interpreted as stops.
- Red/amber is evaluated with the driving behavior based on the settings made in the Behavior at red/amber signal attribute (Editing the driving behavior parameter Signal Control).
- Vehicles may drive at any of the other signal states. When green times overlap, e.g. for conditionally compatible left turns, conflict areas and attribute values take effect that are relevant for mesoscopic simulation (Attributes of meso turn conflicts).
Non signalized intersections
In mesoscopic simulation intersection control is modeled only using conflict areas and their status. The network object type Priority Rule is not taken into account in mesoscopic simulation. Priority rules should not be used in mesoscopic simulation. As different algorithms are used to model movement of the vehicles, meso-specific attributes with individual value ranges are required. The following parameters apply for the behavior of vehicles in conflicting flows:
- Critical gap (Attributes of meso turn conflicts)
- Follow-up gap (Attributes of meso turns)
- Maximum wait time (Editing the driving behavior parameter Meso)
Default values for critical gap and follow-up gap
When importing ANM, Vissim adopts the values for the critical gap and gap time from the import file. If the values are not available in the import file, Vissim sets the following default values. When modeling nodes, you can use these default values for orientation.
For unsignalized intersections (e.g. yield- and stop-controlled) and U-turns the following applies:
| Direction | Critical gap [s] | Follow-up gap [s] |
|---|---|---|
| left major - minor | 3.5 | 2.2 |
| right minor - major | 5.5 | 3.3 |
| minor intersects major | 6.0 | 4.4 |
| left minor - major | 6.5 | 3.5 |
| U-turn major | 3.5 Same as left major - minor | 3.5 Same as left minor - major |
| U-turn minor | 6.5 Same as left minor - major | 3.5 Same as left minor - major |
| Channel island (at the end) | 5.5 Same as right minor - major | 3.3 Same as right minor - major |
For uncontrolled intersections (e.g. priority to right) the following applies:
| Direction | Critical gap [s] | Follow-up gap [s] |
|---|---|---|
| right minor - minor | 5.5 Same as right minor - major | 3.3 Same as right minor - major |
| straight minor - minor | 5.5 Same as right minor - major | 3.3 Same as right minor - major |
| left minor - minor | 6.5 Same as left minor - major | 3.5 Same as left minor - major |
For signalized intersections the following applies:
| Direction | Critical gap [s] | Follow-up gap [s] |
|---|---|---|
| Left turns with counter flow | 3.5 Same as left major - minor | 2.2 Same as left major - minor |
| Right turn on red | 5.5 Same as right minor - major | 3.3 Same as right minor - major |
For roundabouts the following applies:
| Direction | Critical gap [s] | Follow-up gap [s] |
|---|---|---|
| Entry into roundabout | 3.5 | 3.2 |
| Bypass (at the end) | 3.5 (as for entry) | 3.2 (as for entry) |
