Signal time optimization

Visum offers different possibilities to optimize signal times. The following table shows an overview of the procedures as well as their applicability to the signal control types available in Visum.

Procedure	Vissig: Signal group-based programs	Vissig: Stage-based programs	RBC
Signal cycle and split optimization	Yes	Yes	n/a
Network-wide signal optimization	Offset time only	Yes	Yes

Table 120: Overview of the signal optimization procedures

For both procedures, the signal programs set at the time of optimization are optimized. If schedules (Vissig only) are allocated to the signal controllers, you can use the Set signal programs procedure to change the signal program based on the time (and on a calendar day, where applicable). In the input data of the procedures, you define the volumes or travel times the calculation is based on in the case of offset time optimization. This way, the results of dynamic assignment procedures (SBA and PDV only) can be used to optimize signal programs at different times of the day.

Network-wide signal optimization is a flexible procedure in which offset time optimization can be combined with local optimization of split and/or cycle time. By default, the offset time optimization including the analysis is activated. The procedure can also be executed exclusively for the analysis of Signal controller offset times. The combination with split time optimization or signal cycle and split time optimization is optional and not possible in case of signal group-based programs. For signal group-based programs, you can run the Signal cycle and split optimization procedure and the offset optimization sequentially as part of the Network-wide signal optimization procedure.

The signal cycle and split optimization algorithms differ in the two methods procedures above. In contrast to the signal cycle and split optimization procedure, the split and cycle time optimization within the network-wide signal optimization takes into account the arrival of vehicles in platoons as well as the travel time from the last signal controller. In addition, path volumes are taken into account, whereas only turn volumes are considered in the signal cycle and split optimization. For both procedures, it is relevant which optimization method was chosen at the signal controller.

The optimization of offset times is based on the definition of coordination groups. A coordination group is a sequence of signalized nodes whose signal times are ideally coordinated so that a group of vehicles can pass them when the light turns green, thereby minimizing the total wait time. The prerequisite is that the cycle times of the signal controllers permit coordination. For this purpose, a set of possible cycle times - so-called cycle time families - is defined at each coordination group. Coordination groups as well as their cycle times have an effect on Signal cycle and split optimization as well as on network-wide signal optimization.

Note: Optimization regards only those nodes (main nodes), whose effective control type = signalized. If no signal controller is allocated to a signalized node (main node) or if no valid signal program is active, the signal controller is considered to be switched off and not taken into account in the optimization.

In the following, you will find a description of the procedures Signal cycle and split optimization and Network-wide signal optimization.