Simulation/Traffic Lights

From Sumo
Jump to: navigation, search

Normally, NETCONVERT and NETGENERATE generate traffic lights and programs for junctions during the computation of the networks. Still, these computed programs quite often differ from those found in reality. To feed the simulation with real traffic light programs, it is possible to run SUMO/SUMO-GUI with additional program definitions. Also, SUMO/SUMO-GUI allow loading definitions which describe when and how a set of traffic lights can switch from one program to another. Both will be discussed in the following subchapters. Another possiblity is to edit traffic light plans visually in NETEDIT.

Automatically Generated TLS-Programs

  • All traffic lights are generated with a fixed cycle and a default cycle time of 90s. This can be changed with the option --tls.cycle.time.
  • All green phases are followed by a yellow phase. The length of the yellow phase is computed from the maximum speed of the incoming roads but may be customized with the option --tls.yellow.time
  • If the speeds at the intersection are below the threshold of 70km/h (configurable via option tls.minor-left.max-speed), left-turns are allowed at the same time as oncoming straight traffic but have to yield. This is called green minor and indicated with a lower-case g in the state definition. Otherwise, the left-turning stream must use a protected left-turn phase (see below). If no such phase can be built because there is no dedicated turning lane, green minor is allowed anyway but a warning is issued.
  • If a green phase allows for partially conflicting streams (i.e. straight going and left-turning from the opposite direction) and there is a dedicated turning lane, it is succeeded by another green phase with full priority to the partially conflicted streams (this would typically be a left-turning phase). The duration of this phase defaults to 6s and can be customized (or disabled) by setting the option --tls.left-green.time.
  • In reality there are often phases where all streams have red to allow clearing an intersection. SUMO does not build these phases by default. To have each green phase preceded by an all-red phase, the option --tls.allred.time can be used.
  • It is also possible to generate #Actuated_Traffic_Lights by setting the option --tls.default-type actuated. This will generated the same signal plans as above but with green phases that have a variable length of 5s-50s (both values can be set using the options --tls.min-dur, --tls.max-dur).

Typical 4-arm intersections

By default, programs are generated with 4 green phases:

  1. a straight phase
  2. a left-turning phase (only if there is a dedicated left-turn lane)
  3. a straight phase for the direction orthogonal to the first one
  4. a left-turning phase for the direction direction orthogonal to the first one (only if there is a dedicated left-turn lane)

Due to the default timings explained above, the green phases usually have a duration of 31s.

Other Intersections

  • If there are more than 4 roads meeting at an intersection, additional green phases are generated
  • If the roads meeting at an intersection have the highest road priorities on a turning stream, another type of plan may be generated where each road gets the green light for all its streams. This gives a green phase for each road.
  • If a traffic-light junction does not have any conflicting roads (i.e. it models a pedestrian crossing) it will not get a red phase by default. A single red phase may be generated by setting the option

Improving Generated programs with knowledge about traffic demand

  • To get traffic lights that adapt to demand dynamically, built the network with option --tls.default-type actuated. This will automatically generate actuated traffic lights.
  • The tool can be used to modify green phase durations to accommodate a given traffic demand.
  • The tool can be used to modify program offsets to generated green waves for a given traffic demand.

Defining New TLS-Programs

You can load new definitions for traffic lights as a part of an additional-file. When loaded, the last program will be used. Switching between programs is possible via WAUTs and/or TraCI. Also, one can switch between them using the GUI context menu. A definition of a traffic light program within an additional-file looks like this:

   <tlLogic id="0" programID="my_program" offset="0" type="static">
      <phase duration="31" state="GGggrrrrGGggrrrr"/>
      <phase duration="5"  state="yyggrrrryyggrrrr"/>
      <phase duration="6"  state="rrGGrrrrrrGGrrrr"/>
      <phase duration="5"  state="rryyrrrrrryyrrrr"/>
      <phase duration="31" state="rrrrGGggrrrrGGgg"/>
      <phase duration="5"  state="rrrryyggrrrryygg"/>
      <phase duration="6"  state="rrrrrrGGrrrrrrGG"/>
      <phase duration="5"  state="rrrrrryyrrrrrryy"/>

To get started you can copy the tlLogic elements for all traffic lights you wish to edit from a .net.xml file and put them into a new file. Then you only need to change the programID attribute and the program is ready to be modified and loaded

<tlLogic> Attributes

The following attributes/elements are used within the tlLogic element:

Attribute Name Value Type Description
id id (string) The id of the traffic light. This must be an existing traffic light id in the .net.xml file. Typically the id for a traffic light is identical with the junction id. The name may be obtained by right-clicking the red/green bars in front of a controlled intersection.
type enum (static, actuated, delay_based) The type of the traffic light (fixed phase durations, phase prolongation based on time gaps between vehicles (actuated), or on accumulated time loss of queued vehicles (delay_based) )
programID id (string) The id of the traffic light program; This must be a new program name for the traffic light id. Please note that "off" is reserved, see below.
offset int The initial time offset of the program

<phase> Attributes

Each phase is defined using the following attributes:

Attribute Name Value Type Description
duration time (int) The duration of the phase
state list of signal states The traffic light states for this phase, see below
minDur time (int) The minimum duration of the phase when using type actuated. Optional, defaults to duration.
maxDur time (int) The maximum duration of the phase when using type actuated. Optional, defaults to duration.
In a SUMO-TLS definition, time is on the vertical axis and each phase describes all signal states that last for a fixed duration. This differs from typical traffic engineering diagrams where time is on the horizontal axis and each row describes the states for one signal. Another crucial difference is, that in SUMO a new phase is introduced whenever at least one signal changes its state. This means that transitions between green phases can be made up of multiple intermediate phases.

Signal state definitions

Each character within a phase's state describes the state of one signal of the traffic light. Please note, that a single lane may contain several signals - for example one for vehicles turning left and one for vehicles which move straight. This means that a signal does not control lanes, but links - each connecting a lane which is incoming into a junction and one which is outgoing from this junction. In SUMO, a one-to-n dependency between signals and links is implemented, this means each signal may control more than a single link - though networks generated by NETCONVERT or NETGENERATE usually use one signal per link. Please note also, that a traffic light may control lanes incoming into different junctions. The information about which link is controlled by which traffic light signal may be obtained using the "show link tls index" option within SUMO-GUI's visualisation settings or from the according linkIndex attribute of the <connection> elements in the .net.xml file.

The following signal colors are used:

Character GUI Color Description
r FOO 'red light' for a signal - vehicles must stop
y FOO 'amber (yellow) light' for a signal - vehicles will start to decelerate if far away from the junction, otherwise they pass
g FOO 'green light' for a signal, no priority - vehicles may pass the junction if no vehicle uses a higher priorised foe stream, otherwise they decelerate for letting it pass. They always decelerate on approach until they are within the configured visibility distance
G FOO 'green light' for a signal, priority - vehicles may pass the junction
s FOO 'green right-turn arrow' requires stopping - vehicles may pass the junction if no vehicle uses a higher priorised foe stream. They always stop before passing. This is only generated for junction type traffic_light_right_on_red.
u FOO 'red+yellow light' for a signal, may be used to indicate upcoming green phase but vehicles may not drive yet (shown as orange in the gui)
o FOO 'off - blinking' signal is switched off, blinking light indicates vehicles have to yield
O FOO 'off - no signal' signal is switched off, vehicles have the right of way

Traci tutorial tls.png
Example: traffic light with the current state "GrGr". The leftmost letter "G" encodes the green light for link 0, followed by red for link 1, green for link 2 and red for link 3. The link numbers are enabled via SUMO-GUI settings by activating show link tls index.

Actuated Traffic Lights

Based on Time Gaps

SUMO supports gap-based actuated traffic control This control scheme is common in Germany and works by prolonging traffic phases whenever a continuous stream of traffic is detected. It switches to the next phase after detecting a sufficient time gap between sucessive vehicles. This allows for better distribution of green-time among phases and also affects cycle duration in response to dynamic traffic conditions.

To use this type of control, the <tlLogic>-element needs to receive the attribute type="actuated". It also requires the usage of the phase-attributes minDur and maxDur instead of duration to define the allowed range of time durations for each phase (if these values are equal or only duration is given, that phase will have constant duration). Additional parameters may be used to configure the control algorithm further. These may be given within the <tlLogic>-Element as follows:

<tlLogic id="0" programID="my_program" offset="0" type="actuated">
   <param key="max-gap" value="3.0"/>
   <param key="detector-gap" value="2.0"/>
   <param key="show-detectors" value="false"/>
   <param key="file" value="NULL"/>
   <param key="freq" value="300"/>

   <phase duration="31" minDur="5" maxDur="45" state="GGggrrrrGGggrrrr"/>

The value of max-gap describes the maximum time gap between successive vehicle that will cause the current phase to be prolonged (within limits). detector-gap determines the time distance between the (automatially generated) detector and the stop line in seconds (at each lanes maximum speed). If show-detectors is set to true, the generated detectors are shown in SUMO-GUI. The parameters file and freq have the same meaning as for regular induction loop detectors. The examples values are the default values for these parameters.

Based on Time Loss

Similar to the control by time gaps between vehicles, a phase prolongation can also be triggered by the presence of vehicles with time loss. A TLS with this actuation type can be defined as follows:

<tlLogic id="0" programID="my_program" offset="0" type="delay_based">
   <param key="detectorRange" value="100" />
   <param key="minTimeLoss" value="1" />
   <param key="file" value="NULL"/>
   <param key="freq" value="300"/>
   <param key="show-detectors" value="false"/>
   <phase duration="31" minDur="5" maxDur="45" state="GGggrrrrGGggrrrr"/>

Here, the detectorRange specifies the upstream detection range in meters measured from the stop line. Per default (if the parameter is left undefined) the underlying E2 detector is assumed to cover the first approaching lanes completely. The time loss for a vehicle is accumulated as soon as it enters the detector range. If its accumulated time loss exceeds the value of minTimeLoss (current default is one second) seconds a prolongation of the corresponding green phase is requested if it is active. The instantaneous time loss of a vehicle is defined as 1 - v/v_max, where v is its current velocity and v_max the allowed maximal velocity. See [Oertel, Robert, and Peter Wagner. "Delay-time actuated traffic signal control for an isolated intersection." Transportation Research Board 2011 (90th Annual Meeting). 2011.] for details.

Interaction between signal plans and right-of-way rules

Every traffic light intersection has the right-of-way rules of a priority intersection underneath of it. This becomes obvious when switching a traffic light off (either in SUMO-GUI with a right-click on the traffic light or by loading the "off" program).

The right-of-way rules of this priority intersection come into play when defining signal plans with simultaneous conflicting green streams (by using g and G states). These signal plans only work correctly if the right-of-way rules force vehicles from the g stream to yield to the G stream. In most cases, this relationship was set correctly by the default signal plan.

However, when introducing new g/G relationships, correctness is only ensured by loading the network and the new signal plan into NETCONVERT and thus updating the right-of-way rules.

Loading a new Program

After having defined a tls program as above, it can be loaded as an additional-file; of course, a single additional-file may contain several programs. It is possible to load several programs for a single tls into the simulation. The program loaded last will be used (unless not defined differently using a WAUT description). All subkeys of the additional programs must differ if they describe the same tls.

Assuming the program as defined above is put in a file called tls.add.xml it can be loaded in SUMO/SUMO-GUI like this

 sumo -a tls.add.xml ...<other options for network and routes>

It is also possible to load a program which switches the tls off by giving the programID the value "off".

<tlLogic id="0" type="static" programID="off"/>

Tools for Importing TLS Programs

Description from real-world traffic light systems do not arrive in form of SUMO-traffic light descriptions normally. The main difference in presentation comes from the fact that SUMO defines a new <phase> whenever any of the controlled signals changes its state, whereas traffic engineers differentiate between phases and phase transitions.

For an easier import than editing the XML by hand, some tools exists in <SUMO_HOME>/tools/tls.

  • this tool simplifies descriptions because it allows to define the duration of phases for each controlled edge-to-edge connection. Splitting into smaller SUMO-phases because other signals change is done automatically.
  • this tool further simplifies descriptions because it allows to define the start and end times of green-phases per signal group (up to 2 green phases, actually) and the transitions (yellow, red-yellow) are added automatically. The splitting into smaller SUMO-phases is also done automatically.

Alternatively NETEDIT can be used to edit programs using a graphical user interface.

Modifying Existing TLS-Programs

To modify the program of a traffic light it is generally necessary to load a new program. However, in the special case that only the offset shall be modified it is also possible to specify a new offset for an existing traffic light id and programID:

   <tlLogic id="0" programID="0" offset="42"/>

Controlling multiple Junctions with the same controller

In SUMO, a traffic light controller can controll an arbitary number of junctions simultaneously. This is accomplished by one of the following methods:

  • Defining the same tl attribute (the controller ID) for a set of nodes in .nod.xml file when building the network with NETCONVERT
  • Setting the same tl attribute for multiple nodes in NETEDIT
  • Setting the option --tls.join when building the network with NETCONVERT. This will automatically join the traffic lights of nodes in close proximity within a default distance of 20m (customizable by setting option tls.join-dist <FLOAT>).

Note, that in this case the state vector for each phase will be as long as the total number of controlled intersections. Also, the tls indices for the connections will differ from the link indices (as the latter starts with 0 for each intersection whereas the tls indices are unique within a controller).

The generated TLS program will attempt to identify the main directions but usually this needs some manual corrections.

Defining Signal Groups

In SUMO every lane-to-lane connection at a controlled intersection is assigned an index called link tls index. This index is used to determine the state for each phase by looking up the character code at that index in the state vector. The link index can be shown in SUMO-GUI by setting the junction visualization option show link tls index. By default link indices are unique for each connection and assigned in a clockwise manner starting at the north (the same as the junction link index which is used for defining right-of-way rules). When defining joint TLS, the indices continue their numbering in the order of the controlled junctions.

The tls index for each connection can be freely assigned in a .tll.file or by setting attribute linkIndex in NETEDIT. By assigning the same index to multiple connection they form a signal group and always show the same state (simply because they reference the same state index). This allows shortening and thus simplifying the state vector.

Defining Program Switch Times and Procedure

In practice, a tls often uses different programs during a day and maybe also for weekdays and for the weekend days. It is possible to load a definition of switch times between the programs using a WAUT (short for "Wochenschaltautomatik" ~ weekly switch automatism).

Given a tls which knows four programs - two for weekdays and two for weekend days where from 22:00 till 6:00 the night plan shall be used and from 6:00 till 22:00 the day plan, and already defined programs, named "weekday_night", "weekday_day", "weekend_night", "weekend_day". To describe the switch process, we have to describe the switch at first, assuming our simulation runs from monday 0.00 (second 0) to monday 0.00 (second 604800):

<WAUT refTime="0" id="myWAUT" startProg="weekday_night">
   <wautSwitch time="21600" to="weekday_day"/>    <!-- monday, 6.00 -->
   <wautSwitch time="79200" to="weekday_night"/>  <!-- monday, 22.00 -->
   <wautSwitch time="108000" to="weekday_day"/>   <!-- tuesday, 6.00 -->
... further weekdays ...
   <wautSwitch time="453600" to="weekend_day"/>   <!-- saturday, 6.00 -->
... the weekend days ...

The fields in WAUT have the following meanings:

Attribute Name Value Type Description
id string id The name of the defined WAUT
refTime int A reference time which is used as offset to the switch times given later (in simulation seconds)
startProg string id The program that will be used at the simulation's begin

and the fields in wautSwitch:

Attribute Name Value Type Description
time int The time the switch will take place
to string id The name of the program the assigned tls shall switch to

Of course, programs with the used names must be defined before this definition is read. Also, the switch steps must be sorted by their execution time.

Additionally, a definition about which tls shall be switched by the WAUT must be given, as following:

<wautJunction wautID="myWAUT" junctionID="RCAS" [procedure="Stretch"] [synchron="t"]/>

Here, the attributes have the following meaning:

Attribute Name Value Type Description
wautID string id The id of the WAUT the tls shall be switched by
junctionID string id The name of the tls to assign to the WAUT
procedure string enum The switching algorithm to use ("GSP" or "Stretch"). If not set, the programs will switch immediately (default)
synchron bool Additional information whether the switch shall be done synchron (default: false)

It is possible to assign several tls to a single WAUT. It is also possible to assign several WAUTs to a single junction in theory, but this is not done in reality.

A complete definition within an additional-file is shown below. It would trigger switching between programs S1 and S2 for traffic light logic X with an initial program called 0.


  <tlLogic id="X" type="static" programID="S1" offset="0">
    <phase duration="50" state="Gr"/>
    <phase duration="50" state="rG"/>
  <tlLogic id="X" type="static" programID="S2" offset="0">
    <phase duration="30" state="Gr"/>
    <phase duration="80" state="rG"/>

  <WAUT startProg="0" refTime="100" id="w1">
    <wautSwitch to="S1" time="300"></wautSwitch>
    <wautSwitch to="SS" time="800"></wautSwitch>

  <wautJunction junctionID="X" wautID="w1"></wautJunction>


Evaluation of Traffic Lights Performance

Tools For Automatic Detector Generation

Some tools are available which help generating detector definitions for the evaluation of traffic lights. All are located in <SUMO_HOME>/tools/output.

The actuated traffic lights do not require detector definitions to be added as they generate their own detectors for internal use.
  • generates a file which includes areal detectors. All lanes incoming into an intersection are covered with these detectors. The offset from the intersection may be given using the option --distance-to-TLS <FLOAT> (or -d <FLOAT>), the default is .1m. The generated detectors end either after a given length, defined using --detector-length <FLOAT> (or -l <FLOAT>) where the default is 250m, or at the lane's end if the lane is shorter than this length.
  • generates a file which includes multi-entry/multi-exit detectors. Detectors are built for each edge incoming to the traffic light. All lanes of each of these edges are covered with exit points. These point's offset from the intersection may be given using the option --distance-to-TLS <FLOAT> (or -d <FLOAT>), the default is .1m. The incoming edges are followed upstream, either until a given length, defined using --detector-length <FLOAT> (or -l <FLOAT>) where the default is 250m, or another traffic light is reached or no further upstream edge exists. Entry points are generated at these points.

In both cases, the network must be given using the option --net-file <FILE> (or -n <FILE>). The file including the detector definitions to generate may be given using the option --output <FILE> (or -o <FILE>), default is "e2.add.xml" for areal detectors, and "e3.add.xml" for multi-entry/multi-exit detectors. Per default, the areal detectors generated by are writing their measures to "e2output.xml", the multi-entry/multi-exit detectors generated by to "e3output.xml". The output file name can be changed for both scripts using the option --results-file <FILE> (or -r <FILE>). The frequency of generated reports is 60s per default. It can be changed using the option --frequency <INT> (or -f <INT>).