Comparative data analysis in Aimsun Next
August 2024 — Technical note #89
Marga Delgado
Senior Product Specialist
A good data comparison tool is the foundation of our ability to evaluate and analyze differences between simulation results and therefore, make strong, well-supported decisions about transportation network design and management.
The Data Comparison tool in Aimsun Next transport modeling software allows you to perform comparative analysis of results between different Replications, Results, Averages, Experiments and Real Data Sets within a project. The tool can generate a visualization of the comparison on the network 2D view, through the automatic creation of a view mode, as well as a table with absolute and relative differences and a regression plot in the corresponding dialog.
Comparing two simulations
The most typical use case is comparing two simulations or averages under different conditions. The Data Comparison tool gives you a visual overview and a one-by-one comparison of the changes in outputs produced by the change in the network.
For example, in the following image, you can see the difference in travel times produced by a control plan change in which a few extra seconds were added to the North-to-South turns.
Set the following data comparison configuration:
Compare two replications, one with the base control plan, and one with a control plan that has been defined to improve the North-to-South direction.
The point of interest is comparing the travel time at each section in both situations. In the specific case of running the comparison for sections, the Data Comparison view mode is more detailed; instead of just showing the positive or negative difference in colors in the view, it also shows the absolute value of the variable. This way, the magnitude of the difference compared to the absolute value can be assessed.
A band with a width proportional to the value of the minimum of the two values we are comparing (that is, the common part) is colored gray by default, and a second bar coloring the difference between values, is colored green for an increase and red for a decrease by default. These colors are user-defined, so just click on the color to select a different option.
Choosing a particular output to be the Reference or the Compared one is relevant for the interpretation of the colors that will be used to show the comparison in the 2D view, as the comparison will be based on the difference of the two values which will be negative or positive depending on the order the results are selected. That is why, in between the reference and compared results there is a double arrow button to switch positions. In this case, as an increase in the travel time after updating the control plan would be perceived as negative, we will switch the default colors that Aimsun Next offers and use red for increase and green for decrease.
Once the view mode and styles are created, you can modify them in any way you like.
In this case, the difference in section 71533 is much bigger that the difference in section 71525, but the image is not that clear, so we should update the scale:
By clicking on the Comparison – Width view style from the Legend, you can access its definition and update the main intervals, positive and negative values, to apply a width that is proportional between 1 and 80 instead 4 and 40:
You can also check the regression plot by switching to the graph icon:
Comparing with Real Data Sets
Another interesting case of comparison is the one against external data, Real Data Sets (RDS).
In fact, the first RDS vs outputs comparison is available in the Validation folder of the simulation or assignment. This Validation tab already shows a regression plot, the differences table, and can even generate a GEH view mode. In some cases, though, we might want to have a different visualization of this comparison, and this can be obtained through the Data Comparison tool. In the next example, the average travel time collected from probe vehicles for the four sections in the North-to-South avenue is read from an external file. The rest of the sections do not have observations available, so no comparison will be made. Also, in this case the meaning of the sign of the difference is not that relevant, so the choice will be blue for positive and red for negative, for example.
Outputs can also be compared with fixed data. When creating a new Data Comparison, the Compared field will be automatically set to Same as Reference, but other variables will be available. In the next example, dynamic simulation speed results are compared with the section’s Speed Limit.
In this case, the sections that show a thin green line are the ones that achieve free-flow speed (and due to some vehicles’ speed limit acceptance, the observed speed may be higher than the speed limit). The most important information is the thickness of the red band in some sections, where the simulated speed is far from the speed limit.
Sections are the main but not the only object at which we might want to visualize comparison. For example, most of the times RDS counts or flows will be measured on detectors. For the geometric object types that are not sections, because they might not have a significant length, the view mode will color them but will not use the stacked bands we saw in the previous examples. Instead of this, the coloring used in the comparison table for the Relative Difference will be used by default. For example, the visualization of the difference in number of boardings at each transit stop between two different Static Transit Assignments can show this information, which might not be visible when zooming out:
For the next visualization, a spot style was added to be able to zoom out and see the color of the transit stops:
Some extra notes on the Data Comparison tool
- You can adjust the date and duration of the comparison to focus on a specific period by deactivating the ‘A’ button (aggregation) and choosing the interval to analyze. Note that you cannot type any time in these two fields as statistical data has been collected for specific intervals according to the data in the Scenario – Outputs to Generate. Instead, you should use the arrows on your keyboard to select the time.
It is important to remember that the 2D view has its own time widget, and these two are not synchronized.
- You can copy the data as an image or copy the data to the clipboard for use in other applications, such as Microsoft Excel.
- You can also save the configuration by pressing the Save button in the editor dialog.
In summary, Data Comparison in Aimsun Next is a valuable tool for evaluating and analyzing differences between simulation results, facilitating decision-making in transportation network design and management.
