How to model cyclists in Aimsun Next

Technical Note #49
July 2020

By Tessa Hayman

In Aimsun Next you can now add non-lane-based vehicles such as bikes to your model. In this technical note, we will explore how to create cyclists in your model and look at a few possible scenarios.

Before the latest release, the only way to represent bikes was to create a new vehicle type which was bike-sized. However these vehicles would not exhibit bespoke “cyclist behavior” but would behave like a car, i.e., they were restricted to their lane, so we wouldn’t see the effect of cyclists bunching at traffic lights or being overtaken on a single carriageway. Now, in the new release of Aimsun Next 20, we can model “non-lane based-behavior” and better represent how cyclists and motorbike riders behave.

It is important to note that the non-lane-based behavior model for cyclists is intended for city-wide microscopic simulation, focusing on the impact of cyclists over an area, rather than representing realistic trajectories for individual vehicles.

Bikes as a Vehicle Type
Bikes as a Vehicle Type
With a bike lane
With a bike lane

With a separate section
With a separate section
New non-lane-based behavior model
New non-lane-based behavior model


How to allow non-lane-based behavior

Each of these objects must have the model enabled in order for it to be used in the simulation:

  • Experiment
  • Section
  • Vehicle Type

This means that you can limit the non-lane-based behavior to a subset of the traffic and for a certain area of your model.

Activation - Experiment

Activation – Experiment


Activation - Section

Activation – Section


Activation - Vehicle type

Activation – Vehicle type


Vehicle type parameters

You will see that there are two new parameters in the main Microscopic Model tab: Max Lateral Speed and Lateral Clearance. These define how far a vehicle can move laterally within each time step and how much distance must exist between it and another vehicle to enable the non-lane-based model. The minimum lateral spacing between two non-lane-based vehicles is the sum of the lateral clearances of both vehicles. The minimum lateral spacing between a non-lane-based vehicle and a normal vehicle is the lateral clearances of the non-lane-based vehicle only.

Vehicle type parameters

Activating the non-lane-based behavior of the network (experiment and section activation as explained above) activates the lateral perception of all vehicles present on that section. This will make the widths of vehicles and lanes effective parameters of the simulation, so you will need to review these before proceeding!

It’s also a good idea to add a new vehicle class called Cyclists to use in traffic management, signal control and lane types.

Vehicle type

You may want to change the Overtake Speed threshold; this is a percentage of the vehicle’s desired speed, below which it will consider making a lateral movement to overtake. By default this is set to 90%, but you can lower it to make cyclists behave more cautiously.

Vehicle type


How to add a bike box

Bike Box

A bike box also known as an advanced stop line for bicycles.

It is possible to add a bike box at a signal by using signal control groups restricted to certain vehicle classes.

Signal groups
  1. Ensure that you have one vehicle class for Non-cyclists and one for Cyclists.
  2. Add signal groups for Non-cyclists. Change the vehicle class to “Non-cyclist” and set the distance to the length of the bike box e.g., 5m. This will mean that only Non-cyclists will receive the red information, and Cyclists will ride through the red light.
  3. Add the signal groups for Cyclists, these will use the same turns as the signal groups for Non-cyclists but will instead choose the Cyclist vehicle class and a distance of 0m.

Advanced bike box

Advanced bike box


How to create a one-way road with two-way cyclists?

One-way car traffic with two-way bikes

One-way car traffic with two-way bikes

Lane type
It is not possible to use the Two-Way-Two-Lane Overtaking model with non-lane-based behavior – you need to use cycle lanes.

To create a bike-only lane, create a new lane type and call it “Bike Lane”. You can choose whether cyclists must use the cycle lane (reserved compulsory) or if it is optional (reserved optional).

You can then create the one-way section with a cycle lane and then use an additional section in the opposing direction to allow cyclists to travel in both directions. The additional selection would also have a cycle lane applied.