Vissim Importer

Vissim is microsimulation software from PTV.

This importer has the following features:

• To import geometrical data of the network, to define objects like sections, nodes, and centroids.
• To import OD matrices.
• To import control plan (only for INP files) information.
• To import transit information.

A Vissim network must be imported into a new Aimsun document created with the File : New. menu option. It is not possible to import a Vissim network into a previously existing Aimsun traffic network.

Importing from Vissim to Aimsun Next

Importing networks from Vissim reads the network files and creates all the defined elements maintaining correspondence between Vissim and Aimsun objects. This interface supports Vissim *.inp files up to version 5.40 and Vissim *.inpx files up to version 8.0.

Importing a network from Vissim

The first step to import a network from Vissim is to set the directory in which Vissim files are stored. Once the path is selected, the geometry file either *.inp or *.inpx and all matrices *.fma in the folder are automatically added to the editor settings, shown in figure below. However, it is possible to add matrices from any other folder (by clicking on Add button). Only the checked matrices will be imported.

Relation between Vissim and Aimsun objects

Vissim Links and Aimsun Sections

Similarities

Vissim Links have a unique identifier, which is kept in the Aimsun road section External ID.

Vissim Links can have many control points, which define the shape of the link. Aimsun road sections try to keep the original shape but can simplify the number of points.

Aimsun Next road sections will keep information such as the number of lanes, lane width, and the length. Properties related to road type are not imported in this version.

Differences

Vissim does not define turns in the same way as Aimsun Next. Vissim Links can have turns at any part of the link. The importer employs the following steps to create an Aimsun model:

• Split the Vissim Link in segments of length Segment Length (a parameter defined in Vissim Geometry file)
• Read the connectors and associate them to the segment at the beginning of the connector (exit turn) and the segment at the end of the connector (input turn)
• The Aimsun road section will be split depending on the number of turns and the type of the turns at each link segment, as it is shown in the following images:

Vissim Parking Lots and Aimsun Centroids

Each Vissim Parking Lot belongs to a single Zone, indexed by a unique identifier.A Vissim Zone has the same role as an Aimsun Centroid, Therefore when translating the network, the Aimsun Centroid External ID is initialised with the Vissim Zone identifier.

The Vissim Parking Lot defines the connection to or from a Vissim Link. Taking into account the FRACTION parameter, the connection can be either to a section (Fraction = 1.0) or from a section (Fraction = 0.0)

The position of each Aimsun Centroid is calculated from its connections.

Aimsun Nodes

This is the most complex part of the import. Vissim does not define nodes,consequently a process is required to create nodes once all turns have been created in the Aimsun model where:

• Origin Section: All turns from a section must be at the same node
• Destination Section: All turns to a section must be at the same node
• Turn Intersection: A pair of intersecting turns must be at the same node

All these constraints and the fact that a Vissim model can have links which appear inside a junction area might generate nodes that either have too many turns or no grouping turns that should be in the same node and must be edited manually. Examples are shown here.

Control Plans

Vissim Control Plans are only imported from *.inp files, *.inpx files do not have information about phases.

Vissim Control Plans can be defined at any position in a section, thus, the importer will try to locate an existing node and attach the control plan to it. If this fails, it will split the section at the specified position giving a small gap to create the a new node.

Once the node has been selected, only fixed control plans will be imported.

External control plans are imported as Aimsun controllers and connected to the appropriate node.

Vissim Matrices and Aimsun OD matrices

Vissim Matrices list trips between each pair of zones. Vissim also defines the time when the matrix is applied to the network and a scaling factor, which multiplies every value of the matrix. Aimsun Next uses the same definitions, hence a 1:1 correspondence is made between Aimsun matrices and imported Vissim matrices with the exception that the vehicle type is not set as Vissim does not define (in the matrix file) which vehicle is associated with the matrix.

Vissim Vehicle Types

Aimsun Next only imports the length and width of a Vissim vehicle type. All other attributes of Vehicle type are initialised using Aimsun Next default parameters.

Vissim Transit

The importer creates all transit infrastructure (stops and lines) and sets the timetable schedules according to Vissim definition. It also assigns the imported Vissim vehicle type if it is already defined in Vissim network file; otherwise, the Aimsun Next "bus" vehicle type is set.

Vissim Detectors

The importer creates all detectors defined in Vissim. If the detector is linked with any externally controlled junction, the connection between the controller and the detector is also made.