Simulation uses a simplified car following model which distinguishes between two states:
- A vehicle travels at maximum possible speed.
- A temporal distance is kept to the rear end of the preceding vehicle. The temporal distance corresponds to the reaction time, plus the time required by the vehicle to come to a standstill.
This allows us to make the following formulations for the car following model,
where:
| xFollower |
Front end position of following vehicle on current link |
| xLeader |
Front end position of leading vehicle on current link |
| VLink |
Max. link speed |
| τFollower |
Reaction time of following vehicle |
| λLeader |
Effective vehicle length of preceding vehicle |
Table 146 lists the input parameters relevant for the car following model.
|
Object |
Parameters |
Meaning |
|
TSys |
SBA reaction time |
Temporal safety distance (s) |
|
TSys |
SBA effective vehicle length |
Standstill distance plus vehicle length (m) |
|
Links |
V0 |
Max. link speed |
|
Links |
SBA reaction time factor |
Reaction time factor for vehicles on the link, e.g. to calibrate link capacity |
| Links | SBA is reaction time factor transport system dependent | Activates the input option of transport system-dependent factors for the reaction time |
| Links | SBA reaction time factor-PrTSys-PrTSys (PrTSysx, PrTSysy) | Factor for the reaction time of a vehicle of PrTSysx following a vehicle of PrTSysy (one attribute per pair of existing PrT transport systems) |
|
Links |
SBA effective vehicle length factor |
Effective vehicle length factor for vehicles on the link, e.g. to calibrate link storage capacity |
Table 146: Input attributes for the car following model
Table 147 lists additional parameters used in simulation. Please note that link capacity is not an input attribute used in simulation.
The link attributes SBA reaction time factor and SBA factor effective vehicle length are applied by default. As long as the default value of 1 is not changed, this means that the settings of the transport system are adopted. The factors can be used to calibrate the capacity of a link or to adapt to local conditions such as gradients or road parking. For special applications, especially the modeling of autonomous vehicles, a more detailed modeling is required. For detailed modeling, activate the attribute SBA is reaction time factor transport system dependent. Thus, the reaction time factor does not only apply to the vehicle itself, but depends on the combination of the vehicle's transport systems and those of the vehicle in front. If, for example, an autonomous vehicle follows another autonomous vehicle, the factor may be smaller than if the autonomous vehicle follows a conventional vehicle. In general, the reaction time factor can then be defined for all pairs of PrT transport system combinations.
|
Object |
Parameters |
Meaning |
| Links | TSysSet | Number of transport systems allowed |
| (Main)turn |
TSysSet |
Number of transport systems allowed |
| Connectors | TSysSet | Number of transport systems allowed |
|
Lanes |
TSysSet |
Number of transport systems allowed |
|
Lane turns |
TSysSet |
Number of transport systems allowed |
| Links | Number of lanes | Influences the link capacity and, in conjunction with the node topology of the To-node, the lane selection on the link |
| Nodes | Control type | Defines gap acceptance and the parameters used |
| Junction control | Signal controllers, major flow | |
| Node geometry |
Lanes, lane turns |
|
| Node geometry | See Table 148 | |
| TSys | SBA maximum wait time | Maximum time for a vehicle of the minor approach before it forces its entry into the higher ranked traffic stream, even if the time gap is not sufficient |
Table 147: Additional input attributes for simulation
|
Note: In the directory C:\Users\Public\Documents\PTV Vision\PTV Visum 2025/Examples, you can find an example of use on this topic. The PrT Modeling AV example demonstrates how autonomous vehicles can be accounted for in macroscopic models, more precisely in PrT assignments. |
