How to use Attribute Overrides
Technical Note #21
By Maud Chassat
Along with the geometry configurations feature, which allows you to introduce modifications in the shape of your network within the same project file, overrides are useful for modifying attributes of existing objects.
Here’s how to do it.
- Use Table View or manually select a set of objects for which you want to modify an attribute. Select the attribute that you want to modify from the drop-down menu, e.g., Maximum Speed in sections:
Click to enlarge. Figure 1 – Select the objects and the attribute that you want to modify
Once you have set the new values of the attribute for each object, check which objects are affected by the Attribute Override by selecting them all in the Main tab: they should be coloured in red in the 2D view.
Click to enlarge. Figure 2 – Check which objects are affected by the override
- In order to apply an Attribute Override, tick it in the experiment; when the experiment is run, the value set in the Attribute Override will replace the one stored in the object’s properties. This value will also be used by any View Styles when the experiment is selected in the context drop-down box of the view:
Click to enlarge. Figure 3 – Base experiment: no Attribute Overrides
Click to enlarge. Figure 4 – Future experiment: Attribute Override activated
Every process accessing the experiment will take the Attribute Override into account: for instance, V/C ratio calculation will take into account the Attribute Override with new Capacity values.
In macroscopic modelling, you may use VDFs for sections and TPFs for turns. You can easily model a future scenario by creating Attribute Overrides for the parameters you wish to modify, such as user cost or functions. You may create as many Attribute Overrides as alternatives to be tested and create experiments that combine them:
Click to enlarge. Figure 5 – Testing alternative 1 – only motorway
Click to enlarge. Figure 6 – Testing alternative 2 – motorway and street
Attribute Overrides can be used on a very large set of objects: Sections, Lanes, Nodes, Turnings, Centroids, but also non-graphical objects such as PT Lines, User Classes and even Vehicles (just select them in the Project window instead of the view).