Signal cycle and split optimization

If you select signal cycle and split optimization for a node, Visum calculates an optimal cycle time for the signal controller at the node and at the same time an optimal green time split for this cycle time. If several (main) nodes belong to a signal controller, all (main) nodes of this signal controller will be optimized automatically.

The calculation includes the following steps:

1.  Determine the set T of permitted cycle times at the signal controller. If the procedure parameter Use cycle times of coordination groups is active and the signal controller belongs to a coordination group, then only cycle times of the coordination group's cycle time family are permitted. Otherwise, any cycle time (integer [in seconds]) from the interval between the signal controller attributes ICA minimum cycle time for optimization and ICA maximum cycle time for optimization is 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 critical v/s ratios is smaller than or equal to 1. To greater sums always t* = max(T) applies. If the sum of the minimum green time and intergreens for all stages or signal groups are larger than the calculated t*, t* is set to the smallest t of T which is larger or equal to this sum. If no such t exists, t* is set to the sum independently of T.