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Performing green time optimization of stage-based fixed time controllers

You can improve the quality of the signal times table of a selected Vissig SC or all Vissig SCs with the green time optimization of stage-based fixed time controllers.

To this end, Vissim repeatedly calculates simulations of the entire network. All controllers are disabled in the process, except the SCs selected. Thus upstream SCs have no effect. The simulations are continued as long as changes in green times of the stages lead to an increase in the flow (volume) or to a reduction in the average vehicle delay. You can also cancel the iteration. The stage lengths with the best result have the highest flow and the lowest average vehicle delay and are stored in the *.sig file after the optimization.

Sequence of optimization in Vissim

• Vissim determines the average delay of all vehicles that have passed through the nodes on the lanes with signal heads of the signal group, using an automatically created node evaluation for each signal group over the entire simulation run.
• For optimizing, the signal group in which the vehicles have the highest delay is determined for each stage.
• The stage with the lowest maximum average delay is selected as the best stage.
• The stage with the highest maximum average delay is selected as the worst stage.
• A second of green time is deducted from the best stage.
• A second of green time is added to the worst stage.
• If a second can no longer be deducted from the best stage, the second best stage is used. If this can no longer be shortened, the next worst stage is always taken iteratively. If no other stage can be shortened, the optimization is terminated.
• A signal program is considered to be better than another if one of the following criteria is met:
• If the flow formed by the total number of vehicles driven through the node during the simulation run has increased significantly by at least 25 vehicles or by 10% if this is less.
• If the flow has not significantly decreased by 25 vehicles or by 10% and the average delay across all vehicles has decreased.
• If a signal program is better than the best rated, it replaces this as the best. The optimization is continued with the next step.
• The optimization is terminated if one of the following criteria is met:
• Once the signal program does not improve within 10 simulation runs.
• Once the flow decreases by more than 25% compared to the best signal program.
• Once the average delay increases by more than 25%.

Requirements for the green time optimization of stage-based fixed time controllers

Ensure that the following requirements are met:

• The following must be defined in Vissig:
• Signal groups (Defining signal groups in the SC editor)
• Intergreen matrix (Defining an intergreen matrix)
• Stages (Defining and editing stages)
• Stage based signal program (Defining signal programs)
• The following must be defined in Vissim:
• Signal heads (Defining signal heads)
• a surrounding node that contains the junction with the SC for node evaluation (Defining nodes), (Evaluating nodes)
• Adjacent nodes for legs of junction
• The interstages must include the minimum green times and relevant intergreens because the length of a stage can be reduced to zero by optimizing. The signal program must be consistent even if all stages have zero duration.
• The stage-based signal program has a user-defined cycle time and stages of any length. You can use the stage length that was proposed in Vissig when generating the signal program from interstages, for example, an equal distribution across all. You can use the proposed stage length because the original stage lengths are changed by optimizing.
• The demand and the path selection must be defined in the Vissim network. The following must thus be defined:
• Vehicle inputs and routing decisions (Defining vehicle inputs), (Modeling vehicle routes, partial vehicle routes, and routing decisions)
• or for dynamic assignment, parking lots or parking lots and a trip chain file (Defining parking lots for dynamic assignment), (Modeling traffic demand with origin-destination matrices), (Modeling traffic demand with trip chain files)
• a path file (Attributes for the trip chain file, matrices, path file and cost file), (Path search and path selection)
• The route choice does not necessarily have to be defined by static node flow routes. You can also use the dynamic assignment or static routes across multiple nodes because it is only required that the vehicles drive through the nodes of the SC.
• Other signal controls are not considered.

Starting green time optimization for an SC

1.  From the Signal Control menu, choose > Signal Controllers.

The Signal Controllers list opens.

2.  Right-click the entry of your choice.

3.  From the shortcut menu, choose Optimize Signal Control.

Starting green time optimization for all SCs

• From the Signal Control menu, select Optimize All Fixed Time Signal Controllers.