• Routing by Turn Probabilities

Routing by Turn Probabilities

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The jtrrouter is a routing applications which uses flows and turning percentages at junctions as input. The following parameter must be supplied:

• the network to route the vehicles through,
• the description of the turning ratios for the junctions (defaults may be used for this, too), and
• the descriptions of the flows.

A call may look like this:

jtrrouter --route-files=<FLOW_DEFS> --turn-ratio-files=<TURN_DEFINITIONS> --net-file=<SUMO_NET> \
  --output-file=MySUMORoutes.rou.xml --begin <UINT> --end <UINT>

Turn Definitions#

Turn and Sink Definitions
Filename extension	.turns.xml
Type of content	turn and sink definitions
Open format?	Yes
SUMO specific?	Yes
XML Schema	edgerelations_file.xsd

To describe the turn definitions, one has to write an XML file. Within this file, for each interval and each edge the list of percentages to use a certain follower edge has to be given. An example:

<edgeRelations>
   <interval begin="0" end="3600">
      <edgeRelation from="myEdge0" to="myEdge1" probability="0.2"/>
      <edgeRelation from="myEdge0" to="myEdge2" probability="0.7"/>
      <edgeRelation from="myEdge0" to="myEdge3" probability="0.1"/>

      ... any other edges ...

   </interval>

   ... some further intervals ...

</edgeRelations>

The snippet defines that vehicles coming at the end of edge "myEdge0" within the time interval between 0s and 3600s will choose the edge "myEdge1" with a probability of 20%, "myEdge2" with a probability of 70% and "myEdge3" with a probability of 10%. Another possibility to save time on preparing the description is to use default values. The parameter --turn-defaults (-T) <TURN_DEFAULTS> can be used to describe the default ratios that will be used for all junctions for all time steps. <TURN_DEFAULTS> is a list of doubles, separated by a ','. To achieve the same behavior as in the example above, use --turn-defaults 20,70,10. The values will be applied to an edge's following edges beginning at the right edge (20%) and ending at the leftmost edge (10%). As the number of possible followers changes for different edges, the values are resampled for edges which number of following edges differs from the number of given turning probability defaults. Given --turn-defaults 20,70,10 a vehicle using an edge that has two followers would use the follower to the right with 55% probability, the one to the left with 45%.

Automatic generation of turn definitions#

For automatic, yet artificial, turn definitions generation based on the network structure, see generateTurnDefs.py.

You can also generate turn definitions from an existing route file. see generateTurnRatios.py.

Sinks Definitions#

A vehicle leaves the network as soon as it comes to a sink edge. As not all networks have sink edges defined, one can support a list of edges to be declared as sinks using --sinks <EDGE_ID>[,<EDGE_ID>]*. You may also add your sink definitions to a turn-file (XML only):

<turns>
   ... some further turning definitions as above ...

   <sink edges="<EDGE_ID>[ <EDGE_ID>]*"/>
   ... further sink definitions ...

</turns>

If you do not define sinks, the option --accept-all-destinations <BOOL> may be used to declare all edge as possible sinks.

Flow Definitions#

The definitions of the flow is the same as for the duarouter with just a single difference: as it is not known where the vehicle will leave the network as the route it uses is randomly computed, the route must be specified using attribute from and attribute to must be omitted:

<routes>
   <flow id="example0" from="A" begin="0" end="3600" probability="0.5"/>
   <flow id="example1" ... />
   ....
</routes>

Random Flows#

The tool randomTrips.py can be used to generated jtrrouter input by setting options --flows <INT> --jtrrouter.

Overlapping Flows#

By default JTRRouter will route flows through the network and split them at intersections until each part of the flow has reached a sink edge. When such a flow reaches the source edge of another flow, the total traffic is added. The following options can change this behavior:

• --sources-are-sinks (shortcut -S). When this option is set, all flows will terminate upon reaching the from-edge of another flow. Issue #6601
• --discount-sources (shortcut -D). When this option is set, the flow departing at an edge will be reduced by the amount of traffic that has reached this edge from upstream flows. When combined with option --sources-are-sinks, upstream flows will terminate at a downstream edge when the source flow number has been reached.

Additional Options#

As theoretically a route may get infinitely long when a vehicle is forced to take always the same direction, it is possible to limit the route's size using option --max-edges-factor <FLOAT>. This factor, multiplied with the number of the used network's edges is the maximum number of edges a route may have. With the default of 2.0, a route may contain twice as many edges as the network has. Any route longer than this size will be marked as invalid. We assume that for each network this number has to be chosen again.