Method for controlling traffic flow

In an intersection control system comprising a background cycle timer coupled to an intersection supervisor which is provided with a local clock, wherein the intersection supervisor is coupled to an intersection control unit which is operative to control the states of phase signal indicators in responser to signals indicative of a request for intersection passage, a method for controlling intersection passage comprising:

• conveying a signal from said background cycle timer to said intersection supervisor representative of time instant within a fixed length recursive background cycle for synchronization of said intersection supervisor to the background cycle;
• timing specified allowable states of each phase of the intersection with selected ones of presettable timers;
• synchronizing said selected ones of said presettable timers to said background cycle timer by providing a Benchmark signal upon confluence of selected states of selected ones of said timers;
• resetting selected ones of said timers upon occurrence of said Benchmark signal to establish the beginning of a local cycle;
• synchronizing to a designated priority phase referenced to said background cycle timer by means of said intersection supervisor for servicing said priority phase at a preselected time;
• conveying the states of said timers as a single binary service permit signal per phase to said intersection control unit;
• conveying signals representative of selected ones of said intersection indicator states from said intersection control unit to said timers for resetting said timers at selected state transitions;
• and
• switching by means of said intersection control unit said intersection signal indicators of a phase to a condition of intersection access only upon confluence of said service permit signal and said intersection passage request signal.

A system for controlling intersection access at a plurality of intersections comprising:

• a master processor means coupled to a plurality of intersection supervisor means for conveying a background cycle time and selected operating parameters to said intersection supervisor means;
• a plurality of intersection supervisor means, each intersection supervisor means being operative to originate and to communicate permitted state information to an intersection control unit and being generally remote from said master processor means and from an intersection, each said intersection supervisor means being adapted to be coupled to an intersection control unit means at an intersection;
• and
• an intersection control unit means for controlling signal face indicators at an intersection, said intersection control unit means having as input signals service request signals from sensors at said intersection and being operative to independently generate a local cycle of intersection access signals, said intersection control means being further operative to coordinate requests for intersection use which are generated as service request signals from said sensors with said permitted state information when said permitted state information information is communicated to said intersection control unit means, such that responses to requests for intersection use are substantially independent of said master processor means.