Link orientations Lanes and lane turns

Also in macroscopic modeling, lanes and lane turns exist. In the case of lanes, however, it is limited to the through lanes. Lane turns are automatically generated for nodes and main nodes with a standard geometry depending on the number of through lanes on inbound and outbound links. For the areas of application mentioned above, more detail is often required, so pockets in particular must be modeled as special lanes and, as a result, the lane turns of the intersection must also be adapted.

Lanes

For lanes, a distinction is made between through lanes, pockets at the To-node, and pockets at the From-node. Through lanes start and end at a node. The attributes of through lanes cannot differ at these two nodes. Pockets at the To-node are pockets that start on the link and end at a node.

The transport system set permitted on the through lanes of a link corresponds by default to the transport system set of the link. Lanes exist regardless of whether the number of authorized transport systems of the lane is empty or not. However, only transport systems that are also permitted on the link are permitted on the lanes of a link. On the other hand, not all transport systems permitted on the link must be allowed on the lanes. For pockets, the transport system set of the reference lane is used by default. If transport systems are added to or removed from the link, this is also done automatically on the lanes of the link. The transport system set of lanes is considered in the simulation-based assignment, as well as in the export to PTV Vissim.

Lanes (through lanes and pockets) can be inserted and deleted interactively in the junction editor. If through lanes are added or deleted, the link attribute Number of lanes changes. The number of through lanes can also be changed by editing this attribute. Pockets always refer to a through lane (lane attribute Reference lane index) from which they originate or to which they merge. For pockets, a length can be specified. This is used for simulation-based assignment (SBA) and export to Vissim.

Lane turns

A lane turn connects an inbound lane with an outbound lane. For nodes and main nodes for which the Is default geometry attribute is activated, these are created automatically. The updating of geometry and lane turns is triggered by network changes to the objects involved, e.g. by splitting or inserting a link. The node attribute Is default geometry is only automatically deactivated if lane turns are defined that deviate from the default geometry, e.g. if they are inserted at pockets, or if signal groups are assigned to lane turns. The node or main node then no longer has a default geometry. In the event of network changes, the geometry and the lane turns are then retained as far as possible.

In order to define a lane turn, the turn or main turn between the link underlying the inbound lane and the link underlying the outbound lane must be open. This means that it needs to have at least one transport system.

It is usually not desired that lane turns intersect. Two lane turns, for example, intersect if one of them makes a left turn on a right lane while the other goes straight ahead from a left lane. This is yet possible and desired if the left turn is a PrT turn and the other one a PuT turn. This way, for example, a tram in a central position can be modeled.

As with lanes, the transport system set allowed on a lane turn is, by default, equal to the transport system set of the turn or main turn. If transport systems are added or removed on the turn or main turn, this also happens automatically on the assigned lane turns. The transport system set of a lane turn must always be included in the transport system set of the turn or main turn.

The transport system set of lane turns is considered in the simulation-based assignment as well as in the export to PTV Vissim.

The number of lane turns has a significant influence on the results of the impedance calculation at nodes and main nodes.

Link orientations play an essential role when defining node geometries (Geometries). The link orientations are used to determine the amount of legs. Each link has at least four orientation attributes: From and To node orientation, and From and To main node orientation. The two latter attributes are only defined for cordon links of a main node (Main nodes and main turns). The orientations are always undefined for closed links. A link is closed if its transport system set is empty or if the number of lanes is zero. If a link is not closed, it is an open link.

Up to sixteen link orientations can be defined at a node or main node. If a node or main node has more than sixteen open incoming links or more than sixteen open outgoing links, all link orientations will be undefined. At such nodes, no geometry and thus no signalization can be defined.

The allocation of link orientations complies with specific rules. If an incoming link and its opposite outgoing link are open, the To (Main) Node Orientation of the incoming link and the From (Main) Node Orientation of the outgoing link are identical. If there is an incoming link whose opposite direction is closed, you can allocate the same orientation to an outgoing link, as long as its opposite incoming link is also closed. You can also combine incoming one-way roads and outgoing one-way roads in one leg (Geometries) if you give them the same orientation.

Whether Visum calculates the link orientations automatically at a node or main node or not, depends on the attribute Use automatic link orientation. If the link orientations are calculated automatically, the type of calculation depends on the option set under Network > Network parameters > Network objects > Link orientations (User Manual: Specifying the number of link orientations). Normally, the value is set to 8. This means that Visum picks the best orientations from the four main directions (N, E, S, W) and the four secondary orientations (NE, SE, SW, NW). The entry angle of the link at the node or main node is decisive when selecting the orientation. If the orientations do not suffice – i.e. the node or main node has more than eight legs – Visum adds the subordinated secondary orientations (e.g. NNE).

Note: Please note that you can define varying numbers of legs at a node or main node, depending on the number of pairs of incoming and outgoing one-way roads that are given the same orientation.