Traffic Control

Overview and Key Concepts

The traffic control object is used to control traffic in a given area of a travel network. You build a traffic controlled area by connecting network nodes to the traffic control object. These NetworkNodes then become members of the traffic controlled area. Any path between two nodes that are both members of the same traffic control object is designated as a traffic controlled path, and travelers are only allowed onto that path if given permission by the traffic control object. The traffic control object can be in a mutual exclusion mode, where it only lets a certain number of travelers into the area at any given time, or it can use un-timed traffic modes to only allow travelers onto certain path sections at once.

Events

For information on events, see the Event Listening page.

The traffic control object has the following events:

On Entry

On Entry occurs when a traveller enters the area controlled by this traffic control.

It has the following parameters:

Event Parameter	Type	Explanation
Traveler	treenode	The traveller (or task sequence) entering the control area
Network Node	treenode	The traveller's node, an entry to the control area
Next Output Port	int	The output port the traveller will use next

On Entry Request

On Entry Request occurs when a traveller attempts to enter an area controlled by the traffic control.

It has the following parameters:

Event Parameter	Type	Explanation
Traveler	treenode	The traveller (or task sequence) requesting entry the control area
Network Node	treenode	The traveller's node, an entry to the control area
Next Output Port	int	The output port the traveller will use next

OnExit

On Exit occurs when a traveller leaves the control area.

It has the following parameters:

Event Parameter	Type	Explanation
Traveler	treenode	The traveller (or task sequence) exiting the control area

States

The traffic control object does not implement states.

Statistics

The traffic control object does not track any statistics.

Properties

The traffic control object has six tabs with various properties. The last three tabs are common to Travel Network objects. For more information about the properties on those tabs, see:

The remaining three tabs, the TrafficControl tab, the Speeds tab, and NetworkNodes tab are unique to the traffic control object. The properties on these tabs will be explained in more detail in the next three sections.

The TrafficControl Tab

Certain properties on the TrafficControl tab will only appear based on what is selected in the Traffic Control Mode menu. The properties on this tab will be explained in more detail in the following sections.

Traffic Control Mode

This menu defines the method by which the object controls traffic. There are two options:

Mutual Exclusion - Only allows a given number of travelers into the Traffic Control's area, regardless of which paths they are on.
Untimed Traffic Modes - Used if you want to control traffic based on each individual path in the object's traffic control area.

Mutual Exclusion Properties

Mutual exclusion is used to only allow a given number of travelers into the Traffic Control's area, regardless of which paths they are on. Here you simply specify the maximum number value.

Maximum Number in Area - This property only appears when Mutual Exclusion is selected as the Traffic Control Mode. This value defines the maximum number of travelers that are allowed in the traffic control's area.

Untimed Traffic Modes Properties

Untimed traffic modes are used if you want to control traffic based on each individual path in the object's traffic control area. A mode is defined by one row in the modes table. For each mode you can define a set of paths between nodes in the traffic control area. When the traffic control is in a given mode, travelers are only allowed into the traffic control area if the path they are entering on is one of the paths defined in the current mode. The traffic control will stay in the same mode until there are no travelers left in the traffic control area, after which it will take the first traveler that arrives and find a mode that contains that traveler's requested entry path. This is why it is an un-timed mode. There is no limit on the amount of time that a traffic control may stay in the same mode.

The following properties only appear when Untimed Traffic Mode is selected as the Traffic Mode:

Number of Modes - This is the number of modes, or rows in the table. Enter the number of modes you want, and click the Apply button, and the appropriate number of rows will be created.
Number of Entries - This is the maximum number of From/To entries (or columns) that you will need for your modes. If some modes don't need all of the columns, just leave them blank.
Search for Best Mode - If this box is checked, then whenever the traffic control gets an entry request for an entry path that is not in its current mode, it will search through its modes to see if there are any other modes that include all paths already entered as well as the new path. If so, it will change to that new mode and allow the traveler's entry. Note that this may slow down the model, since the traffic control must search the table every time an entry request is made.
Mode Table Entries - The mode table has the following values:
- Max_Nr - This value specifies a maximum number of travelers allowed in when the traffic control is in that given mode. It is much like the maximum number value in mutual exclusion mode.
- n_a - This value is reserved for future development, when timed traffic modes are implemented.
- From/To Entries - For each path of a mode, you specify the node from which the path extends, and the node to which the path extends. Enter the name of the nodes. Note that one entry describes only one direction of a node-to-node connection. Thus to specify both directions of a path, you will need to make two From/To entries, one in each direction.

The Speeds Tab

The Speeds tab has the following properties:

Adjust Speeds as Content Increase

If this option is checked, then the table will be used to adjust speeds of travelers within the traffic control object's area.

Add Row

Click this button to duplicate the selected row. If no row is selected, it will add a row to the end of the table

Delete Row

Click this button to delete the selected row from the table. If no row is selected, it will delete the last row of the table.

Manipulating Speeds with Traffic Controls

You can also use Traffic Controls to modify speeds of travelers as an area becomes more crowded. As the traffic control's content increases, entering travelers will modify their speeds based on the Traffic Control's speed table. For example, if you have entered a row in the table that is a 0.6 speed multiple for a content of 3, then as soon as the content of the traffic control's area becomes 3 or greater, all travelers' max speeds will be decreased to 60% of their normal max speed. Note that the speed change does not take effect until the traveler reaches its next node in the network. If you have an area with multiple traffic controls, then the minimum speed multiple of all of the traffic controls will be applied.

The NetworkNodes Tab

The NetworkNodes tab has the following properties:

The NetworkNode page of the traffic control object lets you edit a traffic control's connections to network nodes. The panel on the left shows all NetworkNodes that are connected to the traffic control object. Select one of these nodes, and the panel on the right will refresh to a new list of traffic controls. The panel on the right shows all traffic controls that are connected to the NetworkNode you have selected on the left. The traffic control you are editing will have an extra " -- This TrafficControl" text, letting you know how this traffic control is situated among other traffic controls. The ranking of traffic controls in the right panel can have a significant effect on the behavior of the network.