For pure split optimization, the cycle time is considered to be fixed.
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Note: Split optimization is not offered for signal controllers of the RBC signalization type. |
Green time optimization for signal group-based signal controllers (Vissig)
A signal group-based signal program must be set for the signal controller. The optimization of signal group-based signal programs results from the following steps of the procedure for stage-based signal programs:
1.
Visum first defines set T of all switching points from the attributes Green time start and Green time end of all signal groups and sorts these in ascending order. For each interval between consecutive times ti and ti+1 in T a stage is generated containing all signal groups available during [ti ; ti+1).
2. An ICA calculation is performed for the signal program. This results in
a. the division of approaches into lane groups
b. the adjusted volume and the saturation flow rate for each lane group
3. The critical lane group is determined for each internal stage in the signal program.
4. Allocate green time based on critical lane group volume and saturation flow rate ratios.
The green time split is calculated as follows:
where
|
Gi |
effective green time for stage i |
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(v/s)ci |
ratio of volume v and saturation flow rate s for critical lane group ci in stage i |
|
Gte |
total effective green time for cycle |
The total effective green time for a cycle is the same as the cycle time deducting all intergreens between consecutive stages. The intergreen between two stages is zero if the stages share signal groups. Otherwise, the intergreen is given by the intergreens of the signal groups.
5. If the overall mean wait time has not improved, cancel and go to 6, otherwise repeat steps 2 to 4 (max. 10 times).
6. The green times of the signal groups are taken from the optimal green times of the stages.
The green time of each signal group results from the green times of all stages containing the signal group. Since by design all these stages are adjacent, this results in a single green time for the signal group.
Green time optimization for signal group-based programs in which signal groups have a second green time is not possible.
Green time optimization for stage-based signal programs (Vissig)
Stages must be defined for the signal controller and a stage-based signal program must be set. If you want to exclude individual stages from the optimization and retain their length from the original signal program, set their Pseudo stage attribute to true. This change must be made in the Vissig window.
Visum executes the following steps to calculate the green time split:
1.
2. Solve the linear optimization problem:
where
|
L |
set of all lane groups |
|
C |
cycle time |
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sl |
saturation flow rate of lane group l |
|
ql |
volume of lane group l |
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tP |
green time duration of stage P |
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3. Carry out another ICA calculation for the optimized signal program.
4. If the total mean wait time has not improved, cancel the calculation and continue with step 5. If the saturation flow rates have changed, go to 2. Otherwise also go to 5.
5. Assign the Green time start and Green time end attributes of the stages the values of the latest optimum solution.
