This page describes simulations of trains in SUMO. To build an intermodal simulation scenario with trains, additional steps have to be taken in comparison to a plain vehicular simulation.
Building a network for train simulation#
Railways can be imported from OSM. They can also be explicitly specified using the existing vClasses.
When importing from OSM the following railway types are distinguished by default (via <SUMO_HOME>/data/typemap/osmNetconvert.typ.xml):
Whenever a railway is electrified, the vClasses rail, rail_electric and rail_fast are permitted to drive there. Otherwise, only vClass rail is allowed.
By loading the additional typemap <SUMO_HOME>/data/typemap/osmNetconvertRailUsage.typ.xml, additional usage information is exported for the edge types:
This will lead to compound edge type ids such as railway.rail|usage.main.
Local track numbers (mostly in train stations) are exported as edge parameter track_ref. These values are shown in the edge parameter dialog and can also be used for coloring (color by param, streetwise).
Bidirectional track usage#
In reality all tracks can be used in either direction if the need arises but many rails are used in only one direction most of the time. In SUMO, bidirectional track usage must be enabled explicitly. This simplifies routing as rails will only be used in their preferred direction most of the time.
Bidirectional track usage is modeled by two edges that have their
geometries exactly reversed and using the attribute
spreadType="center". This will result
in lane geometries that are overlayed exactly. These edges are referred
to as superposed (alternatively as bidirectional rail edges). In the
.net.xml file these edges are marked with
bidi="<REVERSE_EDGE_ID>" but this is a generated
attribute and not to be set by the user.
When Rail signals are placed at both ends of a bidirectional track they will restrict it's usage to one direction at a time.
sumo-gui automatically shows only one of both edges to avoid duplicate drawing of cross-ties. The visualisation option show lane direction can be used to identify superposed edges. (arrows in both directions will be show).
- To show both edges that constitute a bidirectional track, activate edge visualisation option spread superposed. Both edges will be drawn narrower and with a side-offset to make them both visible without overlap.
- To find (and highlight) all bidirectional tracks, use attribute selection and search for attribute bidi with a value of 1
- Create bidirectional tracks as explained here
Importing bidirectional tracks from OSM#
When importing networks from
OSM, rails tagged with
automatically imported as superposed edges.
Handling Problems in bidirectional railway networks#
Commonly, rail networks import from OSM are incomplete in regard to bidirectional track usage. One example would be terminal tracks which a train can only leave by reversing direction. A large number of these issues can be fixed automatically be setting the netconvert-option --railway.topology.repair. To analyze problems with bidirectional tracks, the option --railway.topology.output <FILE> can be used to identify problematic tracks. The option --railway.topology.all-bidi can be used to make all tracks usable in both directions.
By setting the netconvert-option --railway.signals.discard all signals can be removed from a network.
The node type
rail_crossing may be used to define railway crossings. At these nodes trains will
always have the right of way and road vehicles get a red light until
there is a safe gap between approaching trains.
When importing networks from OpenStreetMap, rail crossings will be imported automatically. For other input data sources the crossings may have to be specified via additional xml files or set via netedit after importing.
Kilometrage (Mileage, Chainage)#
Edges support the attribute distance to denote the distance at the start of the edge relative to some point of reference for a linear referencing scheme. When the distance metric decreases along the forward direction of the edge, this is indicated by using a negative sign for the distance value.
The distance value along an edge is computed as:
|edgeDistance + vehiclePos|
Edge distance is imported from OSM and can also be be set along a route in netedit
Negative distance values are not currently supported (pending introduction of another attribute)
Routing on Bidirectional Tracks#
When train tracks can be used in both directions, there is considerable freedom for trains when search a path through the network. To reduce the number of conflicts (when two vehicles want to use the same track in opposite directions), the preferred direction for each track can be defined and factored into the routing decision.
When routes are computed in the simulation, this is done by setting the option --device.rerouting.priority-factor FLOAT. This causes the priority values of edges to be factored into the routing decision with higher values being preferred. At the default value of 0. Edge priority is ignored when routing. When setting a positive value, the edges with the lowest priority receive a penalty factor to their estimated travel time of 1 + FLOAT whereas the edges with the highest priority receive no penalty. Edges with medium priority will receive a penality of 1 + x * FLOAT where
x = (edgePriority - minPriority) / (maxPriority - minPriority)
The priority values can either be assigned by the user or computed heuristically by netconvert by setting the option --railway.topology.direction-priority. This requires that some of the tracks in the network are uni-directional (to unambiguously define the main direction). The assigned priority values are:
- 4: unidirectional track
- 3: main direction of bidirectional track
- 2: undetermined main direction (straight continuation from different directions of unidirectional track)
- 1: undetermined main direction (no continuation from unidirectional track)
- 0: reverse of main direction of bidirectional track
There is a dedicated carFollowMode for trains which can be actived by
carFollowModel="Rail" trainType="<TYPE>" in the
<vType> definition. Allowed values for trainType are
These types model traction and rolling resistance for particular trains. Alternatively, any other car following model may be used and configured with appropriate acceleration / deceleration parameters.
When simulation trains on a network with railway signals, trains will
only enter a block (a section of edges between signals) if it is free of
other trains. When there are no rail signals or multiple trains have
been inserted in the same block, they will automatically keep a safe
distance according to their car following model. When using
will always keep enough distance to the leading train to come to a safe
stop even if the lead train was to stop instantly.
Trains will reverse direction if all of the following conditions are met:
- The head of the train is on a normal edge (not on an intersection / railway switch)
- The whole length of the train is located on rail-edges that allow bidirectional use.
- The speed of the train is below 0.1m/s.
- The train does not have any further stops on the current edge
- The succeeding edges in the train's route are the reverse-direction edges of those it is currently on
There is a "turn-around" connection from the current train edge to the reverse direction edge
When importing public transport stops with option --ptstop-output, all bidirectional edges with a public transport stop will have the necessary turn-around connection and thus be eligible for reversing.
Trains can be split and joined (divided and coupled) at stops.
Splitting a train#
To split a train, the following input definition can be used. The rear half of the train is defined as a new vehicle which depart value split. The train train that is being split must define the 'split' attribute in its stop definition referencing the id of the rear half.
<vType id="train" vClass="rail"/> <vType id="splitTrain" vClass="rail" length="50"/> <trip id="t0" type="train" depart="0.00" from="a" to="c"> <stop busStop="B" duration="60.00" split="t1"/> </trip> <trip id="t1" type="splitTrain" depart="split" departPos="last" from="b" to="e"> <stop busStop="B" duration="60.00"/> </trip>
When defined this way, The rear part of the train will be created as a new simulation vehicle once the first part has reached the stop. After stopping, The front half of the train will continue with reduced length.
Joining two trains#
To join two trains, the following input definition can be used. The front half of the train must define a stop trigger with value join. The rear half othe train must define attribute 'join' referencing the id of the front half.
<vType id="train" vClass="rail"/> <vType id="splitTrain" vClass="rail" length="50"/> <trip id="t0" type="splitTrain" depart="0.00" from="a" to="c"> <stop busStop="B" duration="60.00" triggered="join"/> </trip> <trip id="t1" type="splitTrain" depart="30" from="d" to="b"> <stop busStop="B" duration="5.00" join="t0"/> </trip>
The rear part of the train will be joined to the front part if the followign conditions are met: - the rear part has fulfilled its stopping duration - the front part the train is present and it's back is on the same lane as the front of the rear part - the gap between the trains is less than 5 meters After being joined to the front part, the rear part will no longer be part of the simulation. The front half of the train will stop until the rear part is joined to it. Afterwards it will continue with increased length.
Rail Signal Behavior#
Rail signals perform the following safety functions automatically
- guard the track up to the next rail signal (signal block) so that only one train can enter this section at a time. This prevents rear-end collisions.
- guard the track so that vehicles from different branches (flanks) cannot enter the same section. This prevents flanking collisions.
- guard the track so that vehicles cannot enter bidirectional sections at the same time. This prevents head-on collisions.
- prevent deadlocks on bidirectional sections
Additionally rail signals can enforce train ordering to ensure that a scheduled order at stations can be kept. To make use of this, the following elements can be loaded from an additional file:
<railSignalConstraints id="A"> <predecessor tripId="t0" tl="D" foes="t1" limit="2"/> <predecessor tripId="t0" tl="C" foes="t2"/> <insertionPredecessor tripId="t3" tl="E" foes="t4"/> </railSignalConstraints>
This constrain defines that a given vehicle id (or tripId) can only pass the current signal after some other vehicle ('foe') with the given id or tripId has passed signal 'tl'. The foe vehicle must have been the last vehicle to do so or it must have been one of the last 'limit' vehicles at the time of switching green.
This constrain defines that a given vehicle id (or tripId) can only be inserted on the block leading up to the current signal after some other vehicle ('foe') with the given id or tripId has passed signal 'tl'. The foe vehicle must have been the last vehicle to do so or it must have been one of the last 'limit' vehicles at the time of switching green.
Constraints can be generated using the tool
<SUMO_HOME>/tools/generateRailSignalConstraints.py -r <input-route-file> -n <input-net-file> -a <input-stop-file> -o <output-file>
The tool will analyze the order of arrival at stations (stops).
- If vehicles have successive stops at the same station but reach this station via different tracks, constraints will be generated for the signals ahead of the merging switch. The vehicle that comes later has to wait for the vehicle that comes earlier (
- If vehicles are inserted on the edge of their first stop, a
insertionPredecessor-constraint is generated so that insertion is delayed until the train that stops earlier has passed the signal subsequent to the station.
Rail signals and rail crossings can be controlled with function traci.trafficlight.setRedYellowGreenState. They can also be switched off with traci.trafficlight.setProgram(tlsID, "off"). In either case, normal operations can be resumed by reactivating the default program "0": traci.trafficlight.setProgram(tlsID, "0").
Trains can be controlled just like cars by using the traci.vehicle functions. Furthermore the following functions are available for rail signals:
- traci.trafficlight.getBlockingVehicles(tlsID, linkIndex): Returns the list of vehicles that are blocking the subsequent block for the given tls-linkIndex from the perspective of the closest vehicle upstream of the signal
- traci.trafficlight.getRivalVehicles(tlsID, linkIndex): Returns the list of vehicles that also wish to enter the subsequent block for the given tls-linkIndex (regardless of priority) from the perspective of the closest vehicle upstream of the signal
- traci.trafficlight.getPriorityVehicles(tlsID, linkIndex): Returns the list of vehicles that also wish to enter the subsequent block for the given tls-linkIndex (only those with higher priority) from the perspective of the closest vehicle upstream of the signal
The length of railway carriages, locomotive and the gap between the carriages can be configured using the following generic vType parameters:
- Individual rail cars / coupling / uncoupling cannot currently be modeled