What’s New in Aimsun 8.1


Aimsun 8.1 includes significant improvements to Aimsun 8.0 both at the modelling and platform levels. The Final Release version came out in June 2015.

We’ve summarised the highlights for you below, followed by a quick guide to some of the most significant new features available in travel demand modelling, macroscopic modelling, vehicle-based simulators, the microscopic simulator, the user interface and data analysis.

As always, your feedback is a valuable factor in our continued improvement and addition of new features to Aimsun, so please send your comments to support@aimsun.com.




All-in-one-network geometry changes

The new Geometry Configurations feature allows you to keep multiple geometries in a single Aimsun file. Comparing future alternatives is easier than ever: you can add as many configurations as you like and activate them in different scenarios with a single mouse click. Coupled with Network Revisions, this feature provides a powerful and flexible framework for version control, eliminating errors and duplication.

New macroscopic model

We have addressed that perennial problem of static assignment where the assigned volume often exceeds the available capacity: with our new Quasi-dynamic Network Loading model, you can now evaluate the actual location of bottlenecks after a macroscopic assignment.

Contextual Help

You can now click on the Help button in the bottom left-hand corner of every dialog to pull up context-sensitive help or go to Help -> Content to see the full index of help topics.

HCM 2010 outputs in microsimulation

Aimsun 8.1 processes vehicles’ trajectories on the fly to produce level of service (LOS) and other indicators consistent with the Highway Capacity Manual 2010.

Detailed slope modelling for heavy vehicles

Indispensable for situations in which traffic dynamics are affected by a high HGV mix.


With the new Geometry Configurations feature you can keep multiple geometries in a single Aimsun file.

Above: a block traversed by roads; below: the same block, this time as a park area.

Travel demand modelling

Computational time improvements

  • Distribution is now parallelised
  • Static Assignment with active path results calculation uses less memory than in previous versions
  • Static Adjustment gives the option to carry out more than one gradient iteration before re-assigning the demand, instead of one gradient iteration + one assignment every time

Editing land use attributes

In Aimsun 8.1, distribution attributes are also available in the Table View. All four-step model related attributes listed in the Table View are editable.

Macroscopic modelling

Quasi-dynamic Network Loading Model

Now Static Assignment Experiments allow the activation of the Quasi-dynamic Network Loading calculation as a post-process. Path calculation also needs to be activated (at the Scenario level). As a result, new columns containing the volume of vehicles entering, exiting and queuing (vertical queues) at each section, among others, will be available. A View Mode will show the results graphically:


Static OD departure adjustment

We have introduced the Static OD Departure Adjustment as an additional adjustment method that complements conventional static adjustment.

The Static OD Departure Adjustment generates a profiled demand from the static demand, accounting for the OD routes and link travel times in order to match the time-dependent detector counts.

Using a Path Assignment File as input for the macro

You can use an existing APA file to load and update costs. This means you can start the MSA or Frank & Wolfe static assignments from there instead of starting from an empty network.


  • GEH for static traffic assignment

    The GEH statistic is now available in the Validation folder (in the Macro Assignment Experiment Outputs) after an assignment. Go to Action and calculate the GEH.

  • Automatic macro outputs for subpaths and dynamic groupings after a static assignment

    As of version 8.1, subpaths contain macroscopic outputs as Total Cost and Total Values for function components. Also, with the introduction of dynamic groupings, statistics will be calculated for areas as well.

Vehicle-based simulators

The following features apply to the mesoscopic and microscopic simulators.

Computational time and memory consumption improvements

In Aimsun 8.1 we have significantly reduced the RAM memory and time needed to simulate very large networks.


  • Delay Metering by Vehicle Type

    You can now define different delay times, distinguishing by vehicle type for the delay meterings.


  • Selective meterings for section lanes

    You can now limit meter definitions to certain lanes only, so that they do not cover the whole section.

Traffic management improvements

The Destination Change traffic management action allows you to define several new destination centroids as alternatives. Similarly, the Forced Turn action allows you to define several new sections with specified percentages to modify the next turn vehicles will take. You can define the periodic section incidents to cover more than one lane.


  • Waiting Time in a Virtual Queue

    The delay time in a Virtual Queue has been substituted by the Waiting Time in Virtual Queue output that only takes into account the time each vehicle has spent in a virtual queue. This is available in all simulations.

Microscopic simulator

USA Highway Model

We have implemented a new option in the lane-changing model to boost lane changing in saturated multi-lane highways. Controlled by a parameter called the Percentage of Aggressiveness at the section level, the new model allows vehicles to enter smaller gaps that will gradually recover their normal size via a relaxation process.

New acceleration and speed model for heavy vehicles on slopes

We have greatly improved vehicle behaviour on slopes by including the TWOPAS acceleration model.

The acceleration in uphill slopes now depends on a vehicle’s weight, engine power and front surface as well as on the grade of the slope. The crawl speed, obtained using the equation for a=0, also depends on these parameters.

Details of the model can be found in the “Capability and Enhancement of the VDANL and TWOPAS for Analyzing Vehicle Performance on Upgrades and Downgrades with IHSDM”, 2000, report FHWA-RD-00-078.

We have also implemented a model for the crawl speed on downhill slopes, where heavy vehicles use a lower gear and reduce their speed to avoid overheating the brakes. This speed depends on the vehicle’s weight and the grade and length of the slope. Details can be found in “Feasibility of a grade severity rating system” FHWA-RD-79-116, 1980.



  • Panis et al emission model improvement

    The Panis et al emission model allows you to modify the default values that were previously fixed in Aimsun, (following the values provided in the paper that the model is based on).

  • Public transport stop outputs

    You can now store the arrival and leaving time of each public transport vehicle at each public transport stop.

  • Total number of lane changes

    A new output for the replication shows the total number of lane changes in the whole model.

  • HCM2010 outputs

    Aimsun 8.1 provides HCM 2010-compliant outputs in nodes and sections that are part of signalised node approach, merge area, diverge area and weaving area in a microscopic simulation.

    Sections belonging to the same area or approach will have the same HCM outputs. Here are some of the outputs available for node approaches:


Legion for Aimsun

  • Informal and unsignalised crossings

    Models can now be configured so that, under appropriate circumstances, pedestrians may give way to vehicles at areas designated as unsignalised pedestrian crossings, be those formal or informal crossings.

User interface

Path Assignment object

Aimsun 8.1 allows you to create Path Assignment objects, which should provide a better understanding of where each Path Assignment file has come from and in which scenarios it is in use. We have added corresponding UI dialogs and object editors.

Geometry Configurations

Geometry Configurations (GC) allow you to define variants to the base geometry and apply them to the desired scenario, using the same concept as Attributes Overrides.


Each Geometry Configuration will be defined as an object in the Project window. A Geometry Configuration consists of two lists: the objects that exist only in this GC, and the objects that do not exist in the GC. A list of all GCs is available in the Scenario, so you can choose which ones to activate.

Move layers

You can move and organise layers as you desire. To move a layer among layers, left-click and drag it to its new location.

Decorative Layer

Aimsun will always create a Decorative Layer in every network. Images will be added to the Decorative Layer (instead of the top layer) by default.

Faster drawing

We have optimised 2D to use hardware accelerated graphics.

Solid Lines editor

We have improved the editing process for solid lines in sections, which are the lines that prevent vehicles from changing lanes in a microscopic simulation. The solid lines can be edited directly in the 2D view but in Aimsun 8.1 they also have their own editor.

Node advanced connections visibility

When moving the mouse over a node, Aimsun displays not only the turn movements but also the microscopic simulator connections, which were previously only available via the Advanced node editor.

Decoration: Grey Mode

All the decoration objects based on polygons are greyed out.


Legend Window

We’ve added features to the Legend Window to make it the main means of interacting with the active View Mode.


  • Size multipliers

    The Legend Window features size multipliers to quickly change the width of the sections and the size of both labels and diagrams.


  • Clickable styles

    The style under the mouse is highlighted. For easy tweaking, left-click to see the editor for that style.

  • Object Visibility and Hidden Objects

    We have added visibility switches for frequently used objects. This allows you to set objects as hidden without having to create a specific view style for the purpose. These switches are available through the View Mode edition dialog as check boxes and in the Legend Window as toggle buttons.


You can set the visibility of the following objects in the Legend Window:

  • Nodes
  • Section objects
  • Centroid connections
  • Centroids (show point & show polygon)

View modes

  • Section contours

    When using Pen Width styles, you can draw sections with a darker contour so that the boundaries of overlapping sections are more apparent.


  • Hiding labels

    For less cluttered views, Aimsun hides labels that are larger than the underlying objects.


  • Positioning

    In View Styles of Attribute type, you can now choose from three different locations for labels: at the Beginning, Centre and End of the object. The settings are available in the View Mode Editor.


  • Rounding

    You can now round up numeric labels to multiples of 10,100… and upwards. Objects with values below half the rounding value will be labelled as 0. For example, when rounding to 100, values between 0 and 50 will be labelled as 0, values between 50 and 100 will be labelled as 100.

  • Values shown as percentages

    This option shows the label as its original value divided by 100 and with a trailing percentage sign.


  • New View Style options

    There are now two additional types of spots: Direction Arrows and Direction Rectangles


    We have added a new type of View Style: Stacked Bands. You can use this style to show multiple values on sections at the same time as the width of the section.


Detailed Node View

We have added a new tab to the Node Editor that gives you a detailed view of the node and its turns, when a pen width style for sections has been defined. Aimsun builds a schematic view of the node to avoid overlapping between sections and create enough room for the turns. Turns are drawn as contours, with width proportional to their value.

Experiment Verification

A new experiment-based checker helps you to detect any definition errors prior to running any model.

Data analysis

Link analysis improvements

We have added a Save to a File option and a Retrieve option for a specific Link Analysis. Aimsun saves the filter (the selected choices for Vehicle Type, Origin, Destination, Sections, etc.) and the section volumes in an ALA file and so Filter and View Mode are immediately recovered.

Isochrones, accessibility plot

We have made improvements to the algorithms, which will allow the calculation to run faster.

  • Multiple targets

    You can now set more than one target object. These objects can take on both origin and destination roles.


  • Restrictions

    You can now set restrictions by vehicle type and user class. This means you can exclude certain sections from the calculation, depending on the vehicle types or area classes allowed in each section.

  • Maximum value

    In Aimsun 8.1 you can set a maximum value for the calculation. Objects falling outside this maximum value in the calculation will be set as unreachable.


  • Number of intervals

    You can specify a number of intervals to be taken into account when the view styles are created after the calculation is finished. Aimsun will assign each interval a specific colour.


Data Comparison

We have redesigned the Data Comparison tool to account for both overrides and Geometry Configurations. This allows you to compare inputs between specific scenarios/experiments, e.g., section capacity in two different macroscopic assignments.

It is also possible now, to perform a comparison using multiple object types, for example, you can compare both sections and turns at the same time.

When comparing Time Series sets for different time intervals, the Time Series on the “compared” object is shifted to match the “reference” object. This way Time Series that do not overlap can also be compared, allowing you to compare for example, AM and PM scenarios.


Decision Table

We have redesigned the Decision Table and modified its use slightly. Now it works on sections, areas, and groupings, and is accessible via the Context menu of the selected object.

The Decision Table provides an overall view of the performance of a set of attributes of an object along with a set of data sources, such as experiments or replications.

The different object attributes are set out in rows and the data sources in columns. The best performing data source for each of the attributes is highlighted in green, the worst in red.


Storing Comparison and Decision Table set-ups

You can now store both Data Comparison and Decision Tables set-ups in your project. They will be available in the Project Window in the Data Analysis folder. This feature allows you to store all the information that you have input into the dialogs, so you won’t need to fill them in again.

When double-clicking on a store set-up, Aimsun automatically retrieves the data sources they refer to (replications, for example) and will auto-fill the dialog.