Transit Route Change traffic management action

March 2022 — Technical note #67

Tessa Haymann

Product Specialist at Aimsun

A new feature introduced in Next 22 is the Transit Route Change (Public Transport Route Change) traffic management action. This technical note will go over how to implement the action and ways in which it could be used.

Note from version 22 that the default name for public transport is now transit unless this is changed in the users Aimsun Next preferences to English (United Kingdom).

The Transit Route Change action enables you to alter part of the route of a transit (public transport) line; being a traffic management action, the detour can be activated only in some scenarios or during a portion of the simulation period. Currently this action is only available in micro and meso simulations but not in hybrid simulations.

The most common use case is creating a diversion route for a transit line when there are disruptions along the standard route, for example a blockage caused by an accident or by construction. But, as we will see at the end of this technical note, it can also be used to alter the route in combination with geometry configurations. A more advanced use, via API, is to create flexible-route bus services.


As with other traffic management actions, the transit route change action must be added to either a traffic condition or a strategy and policy. The effect is the same, the difference is purely in the concept: use a traffic condition when you want to represent a given state beyond control, while use a strategy and policy when you want to represent a response plan put in place by a traffic management operator to mitigate the impact of an event.

To add it as part of a traffic condition: create a traffic condition by right clicking in the traffic management menu, clicking new and then traffic condition. To create the action, right click on the traffic condition, click new and then transit route change. The traffic condition must then be added to the scenario in the strategies and conditions tab.

Figure 1: Traffic management options with a transit route change action

To add it as part of a policy: create a strategy by right clicking in the traffic management menu, clicking new and then strategy. Then create a policy within that by right clicking on the strategy, clicking new and then policy. Finally, to create the action, right click on the policy, click new and then transit route change. The strategy must then be added to the scenario in the strategies and conditions tab and then the policy to the experiment in the policies tab.


To activate the action, it is also necessary to set up an activation condition in the traffic condition or in the policy. You have the following options:


  • Always – activate the action for the full modelled period
  • Time – activate the action for part of the modelled period
  • Trigger – activate the action according to network conditions and deactivate according to network conditions
  • External – activate the action via API

To set up the route change, double click on the route change action and select the transit line that you wish to detour from the drop-down box at the top. Its original route appears on the left part of the dialogue. To start select, the line that you wish to detour.

Figure 2: Transit route change configuration dialogue

Then go through the sections in the “original route” list. You’ll see in the view, that the selected section is highlighted dark blue, when you hit the last section before your planned detour, use the top green arrow button to  select the section as the starting section of the detour.

Figure 3: The dark blue section is selected in the interface

In the “Alternative Route” box, select all of the sections that comprise the detour. These will be drawn in red. Don’t forget to assign any bus stops that should be served. After you finish the alternative route, select the section in the “original route” box where the detour re-joins the normal route and use the bottom green arrow to assign it in the “finish detour at section” box.

Figure 4: Transit route change window with a detour
Figure 5: Transit route with detour (in red)

You may then wish to set the dwell times in the bottom box for any new stops on the detour.


You can use this action when creating scenarios with planned or unplanned events (e.g. roadworks or accidents) to create detours that allow transit vehicles to avoid a closed turn or section along their route; if you don’t, they will wait indefinitely for the closure to be cleared.


But there’s another use case, which is supported from version 22.0.1: coding changes of transit routes in conjunction with geometry configurations.


If you used geometry configurations, you are familiar with the need to fully recode all transit lines that go through the locations where the network geometry is altered. With the introduction of the transit route change action, you can recode just the portion of the line that goes through each area where the network geometry is changed.

To do this, first change your view in the user interface to be the view for a scenario with the geometry configuration activated, by selecting it in the menu in the top left of the window.


For each geometry configuration active in the selected scenario, create a traffic condition. Set the activation of the traffic condition to always (including the warm-up).

Figure 6: Select the scenario

For each line that goes through a section removed by the geometry configuration, create a transit route change action in the corresponding traffic condition.


Then when selecting the detour in the route change object, set the last section before the geometry configuration to be the start of the detour. This can be easily identified as these sections will be followed by a grey section instead of a blue one.

Then code your detour through the geometry configuration by selecting the sections created by the geometry configuration.


Finally, select the section at the end of the detour, which is the first blue section preceded by a grey section.


Figure 7: Select the detour through the geometry configuration
Figure 8: Select the start of the detour

When you associate to a scenario a set of geometry configurations, just remember to activate at the same time the corresponding traffic conditions containing the detours for transit lines, and you are all set.

More technical notes

Switching to Python 3

May 2021: Python 2 reached end-of-life status in January 2020. Tessa Hayman gives you some tips on getting your script Python 3-ready for optimum performance in Aimsun Next

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Cite Aimsun Next

Aimsun Next 24

Aimsun (2024). Aimsun Next 24 User’s Manual, Aimsun Next Version 24.0.0, Barcelona, Spain. Accessed on: April. 16, 2024. [Online].


Aimsun Next 24

@manual {AimsunManual,
title = {Aimsun Next 24 User’s Manual},
author = {Aimsun},
edition = {Aimsun Next 24.0.0},
address = {Barcelona, Spain},
year = {2024. [Online]},
month = {Accessed on: Month, Day, Year},
url = {},

Aimsun Next 24

T1 – Aimsun Next 24 User’s Manual
A1 – Aimsun
ET – Aimsun Next Version 24.0.0
Y1 – 2024
Y2 – Accessed on: Month, Day, Year
CY – Barcelona, Spain
PB – Aimsun
UR – [In software]. Available: