1 Exercise: Traffic Management Note about licences: These exercises require a licence for Aimsun Small, Aimsun Standard, Aimsun Professional for Microscopic Simulation, Aimsun Professional for Mesoscopic Simulation, Aimsun Advanced or Aimsun Expert. Traffic management exercises. Introduction. In these exercises, we will see how to create policies to change the destination of vehicles. We will define elements including strategies, policies and VMSs. We will learn how to define Destination changes depending on traffic conditions, and how the VMS message can be changed at specific times to reflect the policy applied.
Transcript
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Exercise: Traffic Management
Note about licences:
These exercises require a licence for Aimsun Small, Aimsun Standard, Aimsun Professional for Microscopic Simulation, Aimsun Professional for Mesoscopic Simulation, Aimsun Advanced or Aimsun Expert.
Traffic management exercises. Introduction.
In these exercises, we will see how to create policies to change the destination of vehicles. We will define elements including strategies, policies and VMSs. We will learn how to define Destination changes depending on traffic conditions, and how the VMS message can be changed at specific times to reflect the policy applied.
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Exercise 1. Network incidents
Load the file ToStartWith_TrafficManagement.ang. The aim of this exercise is to simulate the current traffic model with an incident in the main avenue. The start of the simulation is at 8:00. There is an accident at 8:10 that lasts for 30 minutes, the time it takes to remove the affected vehicles. This accident blocks the two leftmost lanes in the avenue. See the following figure for details: The accident forces also a speed reduction to 20 km/h in the avenue. To recreate this situation a strategy with one policy must be created. The policy will contain two actions: an incident to represent the collision and a speed change to reduce the speed to 20 km/h. The first step is to create a Strategy, go to menu Project / New / Traffic Management / Strategy and a new strategy will appear in the Project Window. Rename it to ‘Emergency’.
Collision
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Click on it with the right mouse button to create a New Policy and double-click on the new policy to set the condition to ‘Time’ and Time from 8:10, duration 0:30:
Rename it to ‘Collision’, click on the policy with the right mouse button, and select New from the context menu and ‘Section Incident’.
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Rename action to ‘Section Incident’. The picture shows how the hierarchy should look:
Double-click on ‘Section Incident’ and modify the dialog as described below and as shown in the next picture:
Use the mouse to select the section colored in red in the picture. A rectangle will appear at the beginning of the section that represents the incident. Move and resize the rectangle to locate as shown in the previous figure. Accept the changes in the editor. Now, the action to reduce the speed to 20 km/h must be created. To do it, click on the policy with the right mouse button, and select New from the context menu. Select ‘Speed Change’.
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Double-click on the action just created and define the parameters as shown in the next image.
Now, the strategy must be activated in the simulation (double click on scenario to access the dialog), under the Strategies & Conditions tab.
And we must also activate the policy in the simulation experiment (double click on the experiment to access the dialog) under the Policies tab.
Once the strategy and the policy have been activated we can simulate the replication. The situation we will get from 8:25 will look like the following figure:
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Exercise 2. Emergency measures
Three different emergency measures are proposed. These measures will be shown in the VMS to inform the drivers, will start taking place five minutes after the collision and will last for 30 minutes. The following image represents the three emergency measures to be taken:
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Emergency measures description:
1. Rerouting vehicles out of the avenue: some vehicles will leave the avenue through the next exit without caring about their destination. The percentage of vehicles that will follow this recommendation (advised trough a variable message sign) will be 40%
2. Rerouting vehicles through a parallel street: vehicles that want to take the congested avenue but have a parallel non-congested street that can
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NW
WU
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take will be advised to do it. The percentage of vehicles that will follow this recommendation will be 50%.
3. Assign an alternative Destination: Vehicles having centroid NW as destination will have a new route assigned going to centroid WU as from there they will be able to get to centroid NW. The percentage of vehicles that will follow this recommendation will be 100%, so all vehicles will change their route.
To evaluate any of these three actions we must create a new policy as the initial time is different than the collision time. This new policy will be renamed as warning.
The three actions explained previously will be created inside this policy as all three will be activated at the same time and will last the same.
1. Force Turning A: A Force Turning action must be added. To do it, please right-click over the policy to open its context menu and select New.
The new action parameters are the following ones:
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2. Force Turning B: Another Force Turning action must be added. To do it, please right-click over the policy to open its context menu and select New.
This change is more complex than the previous one because vehicles must be redirected from a point located far away from the conflict and from the diversion point itself. Through the section where the VMS is a lot of vehicles drive but not all are aiming the avenue where the accident is, so the first thing that must be indicated is that this redirection affects the vehicles going through a specific section only. This can be set in the Section in Path parameter.
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Next image shows that the redirection must affect only vehicles willing to go through section in red, with id = 133.
Furthermore, the redirection must indicate not only next section but a set of sections that contains the lateral street in order to avoid the avenue where the accident is.
An O/D Route that starts in the first section of the redirection and ends where vehicles stop being redirected must be defined. To do it, right-click on Infrastructure to open its context menu and select New… Subpath. Rename it to Lateral Route.
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The O/D Route must be defined like this:
The policy should have the following parameters:
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3. Destination Change:
Lastly, a Destination Change action must be applied on vehicles going under VMS 3 and having original centroid NW as destination. Their destination will be changed and they will be redirected to centroid WU. A Destination Change action must be created. We will rename it to ‘Destination Change’:
Its parameters will be:
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In order to be able to simulate the new actions associated to the Warning policy, the policy must be activated in the experiment:
During the simulation we will observe the following situation:
We observe that the incident in the main avenue does not affect the traffic
there as much as expected due to the new re-routings produced in the network. They mainly affect the lateral lane that gets a high amount of vehicles coming from the re-routings.
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Exercise 3. New control plan
In the last simulation run we can observe that the traffic light in the lateral lane is keeping a huge amount of the vehicles that have been rerouted. Obviously, the current control plan was created to deal with a lower flow of vehicles. This exercise proposes a change in the control plan related to the Warning policy. Current control:
New Control: The movement from South to North gets prioritized.
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The first step is to create a new control plan as shown in the previous image. It will be renamed as ‘Control Plan Emergency’. The next step is to create a new Control Plan Change action in the Warning policy.
Then, the new control plan must be selected in the action:
If we simulate with this new action taken into account, the situation improves:
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Exercise 4. Triggers
Triggers are used to activate policies automatically depending on several conditions. In this exercise, let’s suppose we have a detector in the main avenue just before the conflict zone that is gathering occupancy. What we will do is to activate an action once the occupancy detected is over 80% and we will keep the action activated until the occupancy decreases below 50%. The action to be activated will be like the Force Turning A in exercise 2 but with an 80% of evacuation. The first thing to do is to locate the detector in the network as shown in the following figure:
Afterwards, we will define in the scenario to gather detection data every 2 minutes. This is done in the Output folder in the scenario editor.
The next step is to create the activation trigger and the deactivation one. To create a trigger, the option New / Traffic Management / Trigger must be selected.
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The trigger will be renamed as ‘Trigger High Occupancy’. Its editor, by double clicking on it, will be open to fill the parameters as shown in the next image. Once the editor is open, the first thing that needs to be done is to click on New Condition and then the parameters can be filled in.
The deactivation trigger can be created following the same steps. The trigger name will be ‘Trigger Med Occupancy’:
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Once the activation and deactivation triggers have been created a new policy called ‘Automatic Warning’ must be created and the triggers must be assigned to it as shown in the following image:
A Force Turning action for this new policy must be created. It will be exactly like Force Turning A in exercise 2 except for its Compliance Level Percentage, containing 80% instead of 40%.
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Lastly, in the experiment the ‘Automatic Warning’ and ‘Collision’ policies must be selected before starting a simulation.
If the Occupancy Time Series in the detector is observed, the following graph will be shown, where the red circles indicate when the policy has been activated meanwhile the green ones indicate when the policy has been deactivated:
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Exercise 5. Turn Closure.
Adding to the strategy of the previous “Warning” exercises, we have a new policy action called “Turn Closure”.
These are the parameters that have to be filled in:
When we simulate with the “Warnings” policy enabled.
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Exercise 6. Periodic Incidents
This exercise shows you how to create a traffic condition that simulates the parking in two lanes of the vehicles of one section. In order to do this, it is best to use incidents. It is possible to create multiple incidents that are randomly positioned within a specific area.
We are going to simulate the network using periodic incidents on the fast lane of the section marked in red. The following dialogue demonstrates the parameters that are going to be used:
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If we add the traffic condition to the scenario, we can see the following result:
