Design Petri Net Model

Three Sub Petri-Nets

Tow ways (NS-EW) light synchronization;
In case that one way’s traffic becomes much looser than the other way (lower than threshold, Ľ in this project 20:80 ), it’s traffic light could change to Stop Light (flash Red) and the other way’s light change to the Careful Driving Light (flash Yellow) -- Sub Net 3 is running ;
In case that both ways’ traffic are very looser, it is better to change both ways’ lights to Stop Lights (flash Red)-- Sub Net 2 is running ;
On the other cases, Sub Net 1 is running if it is not forced to stop (Stop Button is pressed);
To be safe and fair, even if the sensor checked out that the lights could be changed from the current traffic lights sub net to the new one, this (sub net) could not change until iteration of the currently running subnet is completed (token goes back to the Control Panel).