Simulation takes detailed node impedances into account. Junction control is modeled using signals and gap acceptance. For signals, a fixed time control must be defined. Should a signal control’s fixed time control and extension change during the assignment period, use daily signal program lists. In daily signal program lists, you can assign times to signal programs, specifying from when they are valid. Nodes that represent approaches with merging operations, e.g. highway ramps, are a special case.
Conflicts
Based on the control type and node geometry data, conflicts between turn flows are determined by analogy with the Highway Capacity Manual (HCM). The control type determines the parameters used for gap acceptance and has an impact on the default values for the parameters critical gap and follow-up gap. Whether the parameters are then taken into account depends on the actual conflicts between the lane turns of corresponding turns. A conflict between lane turns exists if they cross or use the same destination lane. Generally, conflicts between lane turns of a node must be determined for all control types based on node typology. An exception are roundabouts, where vehicles in the roundabout have the right-of-way. In a roundabout, conflicts between lane turns exist when they use the same roundabout segment.
The conflicts calculated between lane turns can be viewed in the junction editor via the relations of lane turns.
Time gaps
Critical gaps and follow-up gaps are used for gap acceptance. The attributes contained in Table 150 at (main) turns that take effect at nodes of all control types except roundabouts. For the control type roundabout, the values are defined at legs. The default values (Table 151) for time gaps are determined based on the HCM and/or HBS, but can be overwritten if required.
The critical gap defines the time headway between two vehicles of the higher ranked traffic stream that allows one vehicle from a lower ranked movement to turn into the desired direction. The critical gap determines how the capacity of the lower ranked movement changes, depending on the higher ranked traffic stream with the right of way.
The follow-up gap is the time headway between the departures of two consecutive vehicles from the same lower ranked approach. Consequently, the follow-up gap determines the saturation flow rate of the minor flow. Follow-up gaps only have an impact on vehicle behavior if they lead to a longer minimum time headway than defined by the car following model.
Table 150 contains input attributes that are taken into account for calculating wait times during simulation.
|
Object |
Parameters |
Meaning |
|
(Main)turn |
Type number |
Requirement for determining conflicts, as turn directions are specified here |
|
(Main)turn |
SBA preset critical gap |
Input value that combined with the attribute SBA use preset critical gap overwrites the default value Activates overwriting of the default value |
|
SBA use preset critical gap |
||
|
(Main)turn |
SBA used critical gap |
Value used for critical gap |
|
(Main)turn |
SBA preset follow up gap |
Input value that combined with the attribute SBA use preset follow-up gap' overwrites the default value Activates overwriting of the default value |
|
SBA use preset follow up gap |
||
|
(Main)turn |
SBA used follow-up gap |
Value used for follow-up gap |
|
Leg |
SBA preset critical gap roundabout |
Input value that combined with the attribute SBA use preset critical gap roundabout overwrites the default value Activates overwriting of the default value |
|
SBA use preset critical gap roundabout |
||
|
Leg |
SBA used critical gap roundabout |
Critical time gap value used for entry into roundabout |
|
Leg |
SBA preset follow-up gap roundabout |
Input value that combined with the attribute SBA use preset follow-up gap roundabout overwrites the default value Activates overwriting of the default value |
|
SBA use preset follow-up gap roundabout |
||
|
Leg |
SBA used follow up gap roundabout |
Follow-up gap value used for entry into roundabout |
|
Leg |
SBA preset critical gap bypass |
Input value that combined with the attribute SBA use preset critical gap bypass overwrites the default value Activates overwriting of the default value |
|
SBA use preset critical gap bypass |
||
|
Leg |
SBA used critical gap bypass |
Critical gap value used for turns from bypass onto next link |
|
Leg |
SBA preset follow-up gap bypass |
Input value that combined with the attribute SBA use preset follow-up gap bypass overwrites the default value Activates overwriting of the default value |
|
SBA use preset follow-up gap bypass |
||
|
Leg |
SBA used follow-up gap bypass |
Follow-up gap value used for turns from bypass onto next link |
Table 150: Attributes for input of critical gaps and follow-up gaps
|
Control type |
Turn direction & flows (right-hand traffic) |
Critical gap [s] |
Follow-up gap [s] |
|---|---|---|---|
|
Two-way stop (stop or yield right-of-way) |
Left turns major flow into minor flow |
3.5 |
2.2 |
|
Right turns minor flow into major flow |
5.5 |
3.3 |
|
|
Straight, intersecting major flow |
6.0 |
4.0 |
|
|
Left turns minor flow into major flow |
6.5 |
3.5 |
|
|
U-turn major flow into major flow |
6.0 |
3.0 |
|
|
U-turn minor flow into minor flow |
6.0 |
3.0 |
|
|
Channelized turn at the end |
5.5 |
3.3 |
|
|
Signal controller |
Left turns with counter flow (permitted) |
3.5 |
2.2 |
|
Right turns on red |
5.5 |
3.3 |
|
|
Roundabout |
Entry into roundabout |
3.5 |
3.2 |
|
Bypass at the end |
3.5 |
3.2 |
|
|
Uncontrolled |
Right turns (only for multiple turns of type 1) opposite vehicles coming from the right |
5.5 |
3.3 |
|
Straight turns opposite vehicles coming from the right |
5.5 |
3.3 |
|
|
Left turns opposite vehicles coming from the right |
6.5 |
3.5 |
|
|
Left turns opposite contraflow |
3.5 |
2.2 |
Table 151: Default values for critical and follow-up gaps listed by control type, turn direction and flow
For All-Way-Stop nodes, the HCM provides for follow-up times at the turns. These follow-up times of the turns depend on the type of the respective turns (right turns, straight ahead, and left turns; the U-turn here corresponds to a left turn) and the geometry group of the From-leg of the turns. The geometry group results from the number of lanes of the From-leg and the number of lanes of the other legs. The geometry group first results in a base time gap (Table 152) and the time gap listed in Table 153 is added depending on the type of turn.
|
Geometry group |
1 |
2 |
3a |
3b |
4a |
4b |
5 |
6 |
| Base time gap | 3.9s | 3.9s | 4.0s | 4.3s | 4.0s | 4.5s | 4.5s | 4.5s |
Table 152: Base time gaps for determining the follow-up times at all-way stop nodes
|
Geometry group |
1 |
2 |
3a |
3b |
4a |
4b |
5 |
6 |
| Left turn | 0.2s | 0.2s | 0.2s | 0.2s | 0.2s | 0.2s | 0.5s | 0.5s |
| Right turn | -0.6s | -0.6s | -0.6s | -0.6s | -0.6s | -0.6s | -0.7s | -0.7s |
| Straight ahead | -0.6s | -0.6s | -0.6s | -0.6s | -0.6s | -0.6s | -0.6s | -0.6s |
Table 153: Time gap to be added to the base time gap for determining the follow-up timess at all-way stop nodes
Merging behavior
Nodes that represent approaches with merging operations are modeled with the control type 'unknown'. Conflicts when passing through the node are neglected, but vehicles from lanes of different inbound links with the same target lane compete for the vacated space on the outbound link. The decision as to which of the vehicles will enter is made at random. Such a situation arises when, at the time of a vacancy on the outbound lane, vehicles are waiting on several inbound lanes. If a vehicle is waiting on one inbound lane only, this vehicle will enter the target lane of the outbound link. The probability of selecting vehicles of an inbound lane can be influenced by the parameter SBA merge weight. This parameter is only effective for nodes with the control type 'unknown'.
To model capacity losses downstream of approaches, the spacing behavior of vehicles can be influenced. The SBA penalty for merging vehicles parameter can be used to increase the temporal spacing of vehicles on the link downstream of the approach by the parameter if the vehicles travel from different inbound lanes to the same target lane. This also applies if the vehicles travel from different lanes of the same link to the same target lane of the following route.
|
Object |
Parameters |
Meaning |
|
Lane turns |
SbA merge weight |
Influences the probability that vehicles on the inbound lane will be used in case of a conflict. The higher the value, the more the probability increases. Default value = 1.0 |
|
Nodes |
SBA penalty for merging vehicles |
Controls a possible capacity drop due to merging operations, for example at highway ramps. At the node, the minimum time headway (SBA reaction time) between vehicles traveling in the same target lanes but coming from different inbound lanes is increased by the specified time. |
Table 154: Input attribute for controlling the merging behavior
Gap acceptance by control type
In all other cases than those listed under Table 6, the critical gap value and follow-up gap value are set to zero. In general, a critical gap of zero means that the vehicles in conflicting flows have equal right-of-way. For conflicting flows that have equal right-of-way this means: If a vehicle has already entered one of the conflicting lane turns, another vehicle must await its reaction time, i.e. wait until the rear end of the first vehicle has left the lane turn. An exception to this are nodes of the control type unknown. Intersecting conflicts in the nodes are neglected. Only when a vehicle enters a destination lane, must you ensure that it has enough space. A critical gap greater than zero means the vehicles in the conflicting flow must give way.
For gap acceptance, this means the following for the individual control types:
- Unknown: For nodes of this control type, all conflicts are neglected. By default, follow-up gaps are zero and thus have no effect.
- Uncontrolled: For nodes with the control type 'Uncontrolled' the vehicle coming from the right has the right-of-way (right-hand traffic). In addition, left turns yield to the traffic of the opposite straight flow. There is also a conflict between opposite left turns, where both vehicles have equal right-of-way.
- Two-way stop (stop and yield right-of-way): Turn direction and flows are determined based on the major flow
- Signal controllers: At signal controllers green times are used to avoid conflicts. An exception are permitted left turns that must yield to the flow from the opposite direction during overlapping green times. For this type of conflict as well as for right turns on red, time gaps are defined. If other conflicts arise due to overlapping green times, then a critical gap of zero is defined, i.e. vehicles are equally entitled to enter the junction.
- Roundabouts: Conflicts arise through use of the same roundabout segments, whereas the vehicle in the roundabout has the right-of-way over the vehicle entering the roundabout. The values used for critical gaps and follow-up gaps are identical for all conflicts.
- All-way stop: For nodes of the control type 'all-way stop', all turns have equal right-of-way. The values used for follow-up gaps are defined based on the HCM and take into account that vehicles need to stop.
Output attributes of simulation
During simulation individual vehicles are taken into account. Output attributes obtained directly from the simulation are additionally shown with the info simulation detail per network object and time interval. In addition, there are output attributes that are obtained based on the simulation results and are thus output only after a simulation-based assignment.
|
Object |
Parameters |
Meaning |
|
Links, (main) turns, connectors |
SBA simulation detail vehicles entered |
Number of vehicles that entered within a time interval |
|
Links, (main) turns, connectors |
SBA simulation detail vehicles exited |
Number of vehicles that existed within a time interval |
|
Links, (main) turns, connectors |
SBA simulation detail vehicles PrTSys entered |
Number of vehicles per PrT transport system that entered within a time interval |
|
Links, (main) turns, connectors |
SBA simulation detail vehicles PrTSys exited |
Number of vehicles per PrT transport system that exited within a time interval |
|
Links, (main) turns |
SBA simulation detail vCur-PrTSys |
average speed of vehicles that have entered the network in the time interval; the value is empty if no vehicle has entered the network in the time interval. |
|
Links, (main) turns, connectors |
SBA simulation detail tCur-PrTSys |
average travel time of vehicles that have entered the network in the time interval; the value is empty if no vehicle has entered the network in the time interval. |
|
Links, (main) turns |
SBA queue length (lane maximum) |
Maximum queue length of link edges assigned to lanes in analysis time interval |
|
Links, (main) turns |
SBA queue length (lane average) |
Average queue length of link edges assigned to lanes in analysis time interval |
|
Links, (main) turns |
SBA utilization |
Corresponds to a scaled density, whereas 100% utilization corresponds to a state in which, during the time interval, vehicles travel at v0 with a minimum following headway. |
|
Links |
SBA density |
Average number of vehicles per km and lane in analysis time interval |
Table 155: Output attributes of simulation
The output attributes for lanes distinguish between the junction area and the (remaining) link. The extent of the junction areas is defined by the longest pocket or the beginning of the channelized turn. There can be junction areas at both ends of a link. In the list of lanes, the through lanes appear as lanes of the node at the beginning of the link and as lanes of the node at the end of the link with the respective junction areas shown in blue in the following figure. Lanes representing pockets or channelized turns have data only for the junction area of the node where they are defined.
Image 145: Schematic representation of a link with through and pocket lanes and the respective junction areas
