These trigger-type objects may be specified within an additional-file and allow the
dynamic adaption of traffic flows and speeds. The syntax for such an
<calibrator id="<ID>" lane="<LANE_ID>" output="<OUTPUT_FILE>"/\>. They can be used to modify simulation
scenario based on induction loop measurements. A calibrator will remove
vehicles in excess of the specified flow and it will insert new vehicles
if the normal traffic demand of the simulation does not meet the
specified number of
vehsPerHour. Furthermore, the speed on the edge will be
adjusted to the specified
speed similar to the workings of a variable speed
sign. Calibrators will also
remove vehicles if the traffic on their lane is jammend beyond what
would be expected given the specified flow and speed. This ensures that
invalid jams do not grow upstream past a calibrator.
<additional> <vType id="t0" speedDev="0.1" speedFactor="1.2" sigma="0"/> <route id="c1" edges="beg middle end rend"/> <calibrator id="calibtest_edge" edge="beg" pos="0" output="detector.xml"> <flow begin="0" end="1800" route="c1" vehsPerHour="2500" speed="27.8" type="t0" departPos="free" departSpeed="max"/> <flow begin="1800" end="3600" route="c1" vehsPerHour="2500" speed="15.0" type="t0" departPos="free" departSpeed="max"/> </calibrator> <calibrator id="calibtest_lane" edge="middle_1" pos="0" output="detector.xml"> <flow begin="0" end="1800" route="c1" vehsPerHour="600" speed="27.8" type="t0" departPos="free" departSpeed="max"/> <flow begin="1800" end="3600" route="c1" vehsPerHour="800" speed="15.0" type="t0" departPos="free" departSpeed="max"/> </calibrator> </additional>
The following attributes/elements are used within the calibrator element:
|Attribute Name||Value Type||Description|
|id||id (string)||The id of the calibrator|
|edge||id (string)||The id of an edge for measuring and calibrating flow. (Either edge or lane must be specified)|
|lane||id (string)||The id of a lane for measuring and calibrating flow (Either edge or lane must be specified)|
|pos||float||The position of the calibrator on the specified lane (currently ignored, see |
|freq||float||The aggregation interval in which to calibrate the flows. default is step-length|
|routeProbe||float||The id of the routeProbe element from which to determine the route distribution for generated vehicles.|
|output||file (string)||The output file for writing calibrator information or NULL|
|vTypes||string||space separated list of vehicle type ids to consider (for counting/removal), "" means all; default "".|
flow elements which are defined as children of the calibrator definition
follow the general format of flow
As the only difference, either the attribute
speed (or both) must be
By default edge calibrators will use
departLane="free" whereas lane calibrators will use
where x is the lane index of the calibrator lane. All calibrators
Decision to insert new vehicles#
The interval (begin, end) defines the time in which calibration takes place. The length of the interval also defines the aggregation period for comparing observed and desired flows. The goal of the calibration is to ensure that the correct number of vehicles are inserted by the end of the interval. At the same time, the space-time structure of existing traffic should be preserved as much as possible.
There is a trade-off between using shorter or longer calibration intervals.
- With shorter consecutive intervals it may happen that vehicles will be removed first and later inserted because they did not arrive with uniform density
- With longer intervals it may happen that vehicles are inserted very lated because the calibrator tries to wait for existing vehicles that might still appear
The freq attribute defines how often a check for inserting vehicles takes place. This value defaults to the simulation step-length. Larger values conserve computation time but may also lead to a tigher clustering of inserted vehicles.
The algorithm for deciding when exactly to insert (and remove) vehicles is described in Erdmann, Jakob (2012) Online-Kalibrierung einer Mikroskopischen Verkehrssimulation. ViMOS 2012, 29.11.2012, Dresden, Deutschland.
Routes of generated Vehicles#
Whenever the measured flow in a given interval is lower than the
specified flow, new vehicles are inserted. If the
routeProbe attribute is
specified, a route is sampled from the distribution of the named route
probe detector. Otherwise the
attribute of the flow is used. Note, that this value may also specify
the name of a route distribution.
Building a scenario without knowledge of routes, based on flow measurements#
Due to their ability of adapting higher as as well as lower flows to a specified value, calibrators may be used to adapt (almost) arbitrary traffic demand to a given set of measurements. One strategy for building a scenario from measurements is therefore, to generated random traffic and use Calibrators in conjunction with route probe detectors. While this can in principle be done with DFROUTER as well, the method described here is more robust for highly meshed networks as found in cities.
Each edge where measurements are given should receive a calibrator and a route probe detector. As soon as the first vehicle has passed the route probe detector, the calibrator will be able to use that vehicles route. For the calibrator to be able to function before the first vehicle, it needs a fall back route which just needs to consist of a single edge (i.e. the edge on which the calibrator is placed).
<additional> <vType id="t0" speedDev="0.1"/> <routeProbe id="cali_edge1_probe" edge="edge1" freq="60" file="output.xml"/> <calibrator id="cali_edge1" lane="edge1_0" pos="0" output="detector.xml" freq="60" routeProbe="cali_edge1_probe"> <route id="cali1_fallback" edges="edge1"/> <flow begin="0" end="1800" route="cal1_fallback" vehsPerHour="2500" speed="27.8" type="t0" departPos="free" departSpeed="max"/> <flow begin="1800" end="3600" route="cal1_fallback" vehsPerHour="2500" speed="15.0" type="t0" departPos="free" departSpeed="max"/> </calibrator> </additional>
Running the simulation with the random demand as well as these
definitions will achieve a simulation in which traffic matches the
specified flows at each calibrator edge. However, the realism of traffic
flow behind (or between) calibrators depends on the fit between random
routes and real-world routes. The importance of this fit increases with
the size and complexity of the network between calibrator edges.