If you execute the Signal cycle and split optimization for a signal controller, Visum calculates an optimal cycle time for the set signal program and at the same time, an optimal green time split for this cycle time. If several nodes (main nodes) belong to one signal controller, the signal programs of the nodes (main nodes) of the signal controller are automatically optimized.
The calculation includes the following steps:
1. Determine the set T of permitted cycle times at the signal controller. If the signal control belongs to a coordination group, only cycle times from its cycle time family are permitted. Otherwise, any cycle times (integer in seconds) from the interval between the signal controller attributes ICA minimum cycle time for optimization and ICA maximum cycle time for optimization are permitted.
2. To each permissible cycle time t from T the following applies:
- Specify optimal green times g*(t) for predefined cycle time t.
- Use ICA to calculate the total wait time at the node for g*(t).
3. As an optimal cycle time t* select the t with minimum total wait time. In addition, set the optimal green time split g*(t*).
The ICA calculation of the total wait time at the node only provides valid values if the sum of the v/s ratios of the critical lane group across all stages is less than or equal to 1. For greater sums, t* = max(T), i.e. the greatest possible cycle time is used. If the sum of the minimum green time and intergreens for all stages or signal groups are greater than the calculated t*, t* is set to the smallest t of T, which is greater than or equal to this sum. If no such t exists, t* is set to the sum independently of T.
