Modeling signal groups and signal heads

Signal groups are the smallest control unit belonging to a controller device assigned a unique signal controller number in Vissim. You can assign a signal controller up to 125 signal groups, depending on its control logic. As signal groups are not visible in reality, Vissim also distinguishes between signal heads and signal groups. A signal group can be assigned to several signal heads that always show the same picture.

Vehicles approaching a red signal will stop at a standstill distance in front of the signal controller (Editing the driving behavior parameter Following behavior).. The default standstill distance is 0.5 m.

Vehicles approaching an amber signal will cross the intersection if they cannot come to a safe standstill at the stop line.

Optionally, you can select a method that calculates the probability of the vehicle stopping or continuing. For this calculation, three driving behavior parameters are required (Defining driving behavior in a driving behavior parameter set).

By default, signal groups and thus all signal heads are updated at the end of every simulation second. If you have specified more than 1 time step per simulation second, signal groups are not switched at each time step. This means that in the network display, each signal header will show a picture that vehicles on its link will respond to in the next time step. Depending on the signal header type, switching is also possible every 1/10 s.

Signal headers allow you to model all common situations with precision. This includes different types of signal groups for several vehicle types on one lane. For instance, for a bus with its separate signal phases, driving on a mixed lane, select the vehicle class of your choice for each signal head.

Note: For any signal controller with conflicting traffic that is allowed to drive at the same time, you need to define priority rules (Creating priority rules).