Aimsun’s vehicle-based simulators offer several traffic management strategies that allow users to modify traffic network conditions, affect driver behaviour or simulate events in the traffic network.

Traffic Management Strategies can be also used to model traffic congestion under either recurrent or non-recurrent traffic conditions. This technical note explains how to alleviate traffic congestion using the following traffic actions:

A. Reserved Lane Deactivation
B. Control Plan Change
C. Speed Change
D. Activate/deactivate traffic actions based on detection data using Triggers
E. Turn Cooperation Model Activation

Background

A. Reserved Lane Deactivation

This action deactivates the definition of a reserved lane making it accessible to all vehicle types. The parameters to define are:

• The section where the reserved lane should be deactivated
• Which reserved lane/s in the section will be deactivated
• The range of segments to deactivate

B. Control Plan Change

This action changes the default control plan defined in the scenario to the one that you set in the action editor.

C. Speed Change

This actions changes the section Maximum Speed. This could be implemented by lane.

D. Triggers

A trigger is an expression that evaluates to true or false. The expression is a collection of conditions based on the current state of a selection of network element statistical attributes (sections and/or detectors). These attributes are evaluated every time that Aimsun collects statistics (for sections) or at the detection interval (for detectors, when the data is aggregated) during a simulation. For more info on this, please see the Aimsun Users’ Manual.

E. Turn Cooperation Model Activation

This action modifies the priorities of selected turns. The cooperation model can be activated on a turn and vehicle type basis. When applied, vehicles with priority at the turn will cooperate with the selected vehicle type, whereas under normal circumstances those selected vehicles would have to yield. The amount of cooperation depends on the % cooperation of the destination section of the priority turn. This is set in the Section Editor. A cooperation of 100% will trigger a zipper behaviour in congested situations. A cooperation of 0% restores the normal give way behaviour.

Implementation

Our example includes a highway with a toll of 8 lanes.

• • The 4 central lanes allow all vehicles to drive through. For those lanes, there is a barrier and cars need to stop and pay the fee.
  • The two rightmost lanes will open only when the following conditions are fulfilled: a) the queue in the mainline reaches the activation detector (occupancy > 50%) and, b) speed drops down to 10 km/h. For those lanes, there is a barrier and cars need to stop and pay the fee.
  • The two leftmost lanes allow only vehicles equipped with e-pass to drive through. For those lanes, there is no barrier and the vehicles need to reduce their speed to 30 km/h to pass through safely. The Speed Change traffic condition will be applied from the beginning of the simulation till the end.

Highway with an 8-lane toll

First, create the Reserved Lane Deactivation, the Control Plan Change and the Speed Change traffic conditions by right-clicking on the Traffic Management object, creating a strategy and then three different policies as presented on the screenshot below:

Create Reserved Lane Deactivation, Control Plan Change and Speed Change traffic conditions

Second, create the triggers to activate and deactivate these traffic actions. In this example, we will use detection interval of statistical values such as speed and occupancy. To create those triggers, follow the process presented on the screenshots below:

Create the triggers to activate and deactivate these traffic actions

Here is the simulation progress step by step:

The simulation starts. Once the queue reaches the Activation Detector (occupancy > 50% and speed < 10km/h) then traffic conditions will be activated. This means that the two rightmost lanes will open for all vehicles and the new control plan will be applied to serve traffic more efficiently by increasing the total capacity of the section. Activation of the traffic actions will be recorded on the Aimsun log.

The queue reaches the Activation Detector and activates Traffic Conditions

The two rightmost lanes opened to serve regular cars. A new control plan is applied:

Once the queue leaves the deactivation detector, then the two rightmost lanes will close again.

However, the Control Plan Change Action will continue to be active till the queue in those lanes disappears completely (occupancy = 0 and speed > 10km/h):

All changes will be shown in the Aimsun log.

Finally, here’s an example of the Turn Cooperation Model Activation.

The first step is to define the node and the desired non-priority Turn as well as the vehicle class that will be affected by this traffic action.

In this example, we will set Lane Changing – Cooperation to 100% for the destination section.

The images below show the difference between conditions when traffic action is activated or deactivated.

A. Before activating the traffic condition:

B. After activating the traffic management: