Transportation Systems Simulation - A Tutorial for Multi-Modal Simulation Using VISSIM/Intersection: Network Objects

Signal Heads

Next you need to add the signal controller related objects that will enable the inputs (detectors) and outputs (indications) that will interact with the signal controller to give the green to the appropriate movement as programmed.

1. Select the Signal Heads from the Network Objects list.
2. Right-click on a link near the intersection to bring up the shortcut menu.
3. Select Add New Signal Head from the list. This will open the Signal Head window which allows you to modify the behavior of each signal head.
   • No. field is a sequential number for each signal head in the simulation.
   • Lane shows you which lane the signal head is in.
   • At box shows how far from the beginning of the link the signal head is placed.
   • SC show which Signal Controller ID is to be used for this signal head.
   • Signal Group identifies which signal group (phase) to assign to this signal head.
   • Type box allows you to modify the type of indication. You can choose Circular, Left arrow, Right arrow, invisible.
   • Name box allows you to give this signal head a unique and meaningful name to better identify it later.
   • Vehicle Classes box allows you to select which type of vehicles will be affected by this indication

When placing the signal heads, be sure to place them near the stop bar along each link. You can reposition the signal heads by clicking and dragging them to their new location. Once you have placed all of the signal heads your intersection should look similar to the figure below.

Note: In some circumstances the intersection will not operate as reality if signal heads are placed on links, it is often necessary to place on connectors.

Tip: you can duplicate signal heads by holding down Ctrl and right clicking on an active signal head. You can then drag it to the new location of the duplicated signal head. Don't forget to modify its parameters to make sure it is identified properly and acts appropriately.

Stop Signs

Some intersections have a dedicated right-turn pocket with its own indication. If this is the case, then a stop sign is actually used to actuate the right turn indication so that vehicles can still make a permissive Right Turn On Red (RTOR).

1. Select the Stop Sign from the Network Objects list and place it similarly to a signal head.
2. When the Stop Sign edit window opens, click on the RTOR tab and modify the Name
3. Check the Only on Red check box
4. Select the appropriate SC and SG as appropriate. See figure below.

Note: If you do have a right-turn indication, then is usually programmed by a vehicle overlap in the signal controller. Remember that each SG must has a unique number in the controller. In this example, we use 13 for the right turn overlap. (1-8 for vehicles, 9-12 for PEDs, 13-16 for overlaps.) Make sure the overlap's parent signal groups are also programmed correctly in the signal controller parameters.

Detectors

Detectors are used at traffic signals to determine when a vehicle is at or approaching the intersection. In the real world, detectors are often inductive loops cut into the roadway, video detection using cameras or are detected with the use of RADAR technology. No matter how it is achieved, detection allows you to actuate (reacts to vehicles) the traffic signal so that when a vehicle is not there, it doesn't turn green. In VISSIM, detectors allow you to place detectors onto roadway links so that your traffic signal can react when vehicles approach the intersection.

1. Select Detectors from the Network Objects list.
2. Right click on a link prior to the stop bar and select Add New Detector from the shortcut menu.

The Detector edit window will appear allowing you to modify the parameters of each detector (see figure below). Here are the parameters of interest:

• Port No.: this should link to the detector number in your signal controller. Note: this is not the signal group number but rather the number you gave the detector.
• Length: This is the length of the detector. Typically detectors are 6’ long and are often placed in pairs or groups in each lane. A typical way to simulate this is use 50 foot detector in the left turn lanes, 18 foot detectors at the through lane stop bar and 6’ detectors in the through lanes approaching the intersection. Note: right turn pockets typically do not have detection.
• Name: is where you can give each detector a unique and meaningful name.
• SC: selects the Signal Controller, by number, to use.
• Type: This defines how the detector is to be used. There are the following detector types:
  • Standard: This is a standard detector that places a call to the signal controller whenever a vehicle is present on it.
  • Presence: This type of detector will only send a call to the controller when the associated signal group (phase) is red allowing the controller to know there is a vehicle waiting to be served.
  • Pulse: This type of detector will only place a call to the controller when the associated signal group (phase) is green, letting the controller know that a vehicle is approaching and to extend the green longer so the vehicle can make it through.
  • PT Calling pt: This detector type is for use with Public Transit and thus is not covered in this tutorial.

In the Activations tab, you can select which vehicle types are able to activate the detector.

In the figure below, you can see a typical way to setup detectors at a traffic signal.

Tip: Detector placed in the same link will all change to be the same. So if you place 2 or 4 detectors along the same link, all of them will be linked together and act the same way. For this reason, when using detectors at traffic signals, it is best to set them up as Standard so they both call and extend phases.

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