Exchanging data between Aimsun Next and SATURN
September 2024 — Technical note #90
Dimitris Triantafyllos
Senior Product Specialist
Aimsun Next can exchange data with SATURN either by reading specific input and output SATURN files to build an Aimsun traffic network or by exporting an Aimsun traffic network to write SATURN format files.
The most common use cases for exchanging data between Aimsun Next and a SATURN model are:
- Importing a Base Network: A SATURN model can be imported and thus a new Aimsun Next network including several macroscopic parameters is created from the SATURN files. Saturn OD matrices, routes, flow speed curves and traffic states can be also imported.
- Updating the Base Network: A SATURN model can be imported into an existing (base) network. So, the same Aimsun Next document file will include the base, scheme and forecast scenarios; everything on a single map. Aimsun Next SATURN importer checks for differences and imports only the differences between the base and the new model by creating new objects/attributes or updating the existing ones.g. by creating new matrices for different time periods or by creating Attribute Overrides or Geometry Configurations to hold the differences between the existing network and the new imported SATURN model. It can also import the demand from a SATURN model and update it.
- Exporting a Network: Exporting a skeletal network file and a set of matrix files from Aimsun Next suitable for input to SATURN software. The selection of the control plan, transit, geometry configurations, attribute overrides and the demand for the network and matrices export is controlled by selecting a dynamic scenario.
Requirements
This interface requires a license for both Aimsun Next and for the Planning Software Interface extension (comes with the Expert edition).
Importing a Base Network
- The SATURN Network file (.DAT) contains all the basic information needed to import the SATURN network into Aimsun Next.
Note: In general, importing a model from third-party software requires a good knowledge of the third-party software and a deep understanding of the model. The importation process is expected to be repeatable, with settings being corrected each time.
- Launch the Aimsun Next software and select the option New Project. Depending on the location and the characteristics of the study area, you will need to configure the options shown below:
- Template
- Coordinate System
- Rule of the Road
[TH1]Its not clear here that you can import multiple saturn models into Aimsun Next and that it will create base, scheme, forecast year etc networks on a single map. Aimsu Next checks for differences and imports only the differences between the models as AOs and GCs
In the Network Tab, you will need to set the SATURN Network file (.DAT) and, if provided, set the GIS File (.GIS). In the options Transit Start Time and Transit Duration, set the values from the SATURN timetable. In this example, the SATURN file is imported for the first time in an empty Aimsun Next document and therefore the option Import as Base Network must be checked.
In case a SATURN model is already imported in the Aimsun Next document then the option Import as a Base Network should not be selected. The importation process will then find only the differences between the imported SATURN data and the current Aimsun Next network and will automatically create Attribute Overrides (to import different values for the same objects in both networks) and/or a Geometry Configurations (to import new or hide non existing objects in the new network). It is possible to import various SATURN models of different years and/or different scenarios in the same Aimsun Next document file.
4. In the User Class Tab, you will be asked to set the mapping between the SATURN and the Aimsun Next Vehicle Types and Aimsun Next Trip Purposes. The Saturn User Class and Saturn Vehicle Class are automatically read by the SATURN Network file (.DAT) from field 88888. The Aimsun Next Vehicle Types and Aimsun Next Trip Purposes that are pre-coded in the template should be selected per Saturn Vehicle Class. The template defined at the beginning of the project could have those Aimsun Next Trip Purposes created or choose the option Create New from the drop-down menu.
In the end of the SATURN data file, the field 88888 contains for each Saturn User Class, several attributes; among those attributes may be the pence per minute (PPM) and pence per kilometer (PPK) that are used in the calculation of the generalized cost inside the SATURN VDF cost function. In the example (see snapshot below) for the Car in Work User Class, the PPM = 44.5 and the PPK = 16.4 respectively. In addition, there may be weights per user class (in this example 16.1 and 8.0) that are multiplied with other section/turn/connection attributes adding an extra cost (tolls, penalties etc.) in the generalized cost function. See in detail, the description of the 88888 records in the SATURN Online Help Manual.
5. The SATURN importer reads SATURN Knobs files. The Knobs files are a source of additional data for the sections, turns and centroids in the SATURN model. Usually these are text files (.txt or .dat). These files may contain information related to cyclist flow data (to be imported as additional volume), toll charges, turn delay penalty data or any other information that has been used in the most recent model.
In the Extra Files Tab, you can optionally set Knobs files (if provided) to import additional SATURN information that is not included in SATURN Network file (.DAT). This information will be then imported into Aimsun Next columns of specific objects (sections, turns, centroid connections). Based on the data in the file, you can define the separator or activate the option Dutch format.
When a Knobs file is added to the list, you will be asked to provide mappings between the fields in the file and the attributes of the object types (section, turn or centroid connection). Once the Knobs file is read, you double click on it and the mapping dialog will pop up automatically. The columns in the Knobs file are listed and attributes from a section, turn or centroid connection selected to receive the imported values. To add a new attribute to hold the Knobs data from a column, select Mapping Type: Direct Column, then select Column: New and set the New Column Name.
Knobs data can also be imported into existing section columns translating:
- Travel Time to Speed considering the length of the section: if Free Flow Travel Time data are available in a Knobs file (and need to be updated), these can be used to calculate the Speed limit at section level.
- Travel Time to Speed only for the buffer network sections: if Free Flow Travel Time is available for the buffer network sections only, they can be used to calculate the Speed limit of those sections.
- Lane Capacity to Section Capacity multiplying the lane capacity by the number of lanes.
Here are a few examples importing Knobs files in the Aimsun Next network objects:
- Example of importing extra toll costs in Aimsun Next as new section attributes: “SATURN tolls 1”, “SATURN tolls 2”, “SATURN tolls 3”
- Example of importing cyclist flows in Aimsun Next to existing attributes, as section and turn additional volumes:
- Example of importing SATURN attributes (..) as new Aimsun Next columns setting custom names.
Access the Saturn Importer/Exporter to find detailed information how the Road Sections (lanes), the Road Types, Turns and Control Plans, User Classes are translated from the SATURN files and imported into Aimsun Next.
SATURN simulation flow data (.txt) can be used as a Traffic State in Aimsun Next. To import those data, in the Traffic State Source File box, select the Saturn Network Flows file. Find more information in Saturn – Traffic State.
Two different route types can be imported from a SATURN network file. The first defines Transit Lines (public transport lines), the second defines paths between two centroids. Find more information in Saturn – Routes Import.
In the Matrix tab, you can import the OD matrices from SATURN to Aimsun Next. The importer only loads OD matrices in standard real format or standard integer format options. It is possible to update matrices in an existing Aimsun document later by using the importer. Find more information in Saturn – Demand Import.
In the Road Type tab, you can automatically categorize road types in Aimsun Next by inferring from the SATURN parameters for each link. This can be done using either the speed or capacity values of the imported section.
Cost functions
A new SATURN vehicle delay function (VDF) will be automatically created. Please note that this is subject to change based on project requirements. Find more information in Saturn – Cost Function Import.
While the SATURN VDF is designed to cover most common use cases, you may need to adjust it to fit your project requirements. Therefore, it is essential to have a thorough understanding of the SATURN model elements before importing those into Aimsun Next. In the VDF, you will find useful comments to help you make the correct decision for every use case.
Important notes:
To learn more how SATURN Importer handles roundabouts see in Saturn Importer – Roundabouts
Every time you import SATURN files in Aimsun Next, an .xml file is created storing all settings performed in the first importation effort. The next time that the user tries to re-import, by loading the SATURN network file, all files and settings will be automatically setup to reproduce the previous importation process. To avoid the auto-complete, you can remove the .xml file from that directory.
Exporting a Network
To export an existing Aimsun Next model to SATURN file, select File -> Export -> Saturn Network. The export dialog is used to select the destination folder for the exported file, the filenames for the network and the matrices as well as the dynamic scenario which has the objects (Master Control Plan, Traffic Demand, Transit, Geometry Configurations, Attribute Overrides) specified.
This interface always generates .DAT files. Note that only fixed control plans are exported from Aimsun Next to SATURN files.
The OD matrices that belong to the traffic demand are exported with following naming convention: Matrix File Name value+N, where N is the number of the matrix exported.
To learn how Nodes, Turns, Link Areas, Centroid Connections, Node Position Area and Transit Area are exported, check the Saturn Exporter.
