REAL-TIME NETWORK DECOMPOSITION AND SUBNETWORK INTERFACING

NEW METHODS OF DECOMPOSING NETWORKS AND INTERFACING THE RESULTING SUBNETWORKS ARE BEING DEVELOPED AS PART OF THE CONTINUING RESEARCH AND DEVELOPMENT EFFORT TO IMPROVE REAL- TIME URBAN TRAFFIC CONTROL. THE BASIC CONCEPTS AND ALTERNATIVES ARE INTRODUCED IN THIS PAPER. NETWORK DECOMPOSITION MAY BE REQUIRED WHEN THE NETWORK GEOMETRY IS NOT UNIFORM AND/OR WHEN THE TRAFFIC CHARACTERISTICS WITHIN AN AREA ARE NOT UNIFORM. DECOMPOSITION IS NOT SUCCESSFUL UNLESS TWO TASKS ARE ACCOMPLISHED: (A) SUBNETWORK DETERMINATION ACCORDING TO CERTAIN CRITERIA AND (B) INTERFACING THE VARIOUS SUBNETWORKS. THE TWO GENERAL WAYS IN WHICH SUBNETWORKS MAY BE DEFINED ARE FIXED DEFINITION AND REAL-TIME SUBNETWORK DEFINITION. FIXED SUBNETWORKS ARE DEFINED FROM GEOMETRICAL AND OTHER CONSIDERATIONS. REAL-TIME SUBNETWORK DEFINITION IS BASED ON TRAFFIC DYNAMICS. TO DEFINE SUCCESSFULLY SUBNETWORKS IN REAL TIME, TWO ELEMENTS MUST BE PRESENT: (A) A CRITERION BY WHICH IT CAN BE DETERMINED THAT AN INTERSECTION IS A "CANDIDATE" FOR CONSIDERATION AS PART OF A SEPARATE SUBNETWORK AND (B) A PROCEDURE BY WHICH THESE CANDIDATE INTERSECTIONS CAN BE GROUPED INTO A WORKABLE SUBNETWORK. THE PROPOSED CRITERION FOR CANDIDACY IS OFFSET ERROR -THE DIFFERENCE BETWEEN A REALIZABLE AND AN IDEALIZED OFFSET. AMONG THE GROUPING PROCEDURES ARE TWO GENUINELY REAL-TIME METHODS (RECTANGULAR SUBSET AND CONNECTIBLE SET) AND ONE PSEUDO REAL-TIME METHOD. INTERFACING SUBNETWORKS CAN BE A DIFFICULT TASK. IN THE SPECIAL CASE WHERE THE TWO AREAS HAVE THE SAME SIGNAL CYCLE, INTERFACING IS ACCOMPLISHED VIA A "DELTA OFFSET." THIS DELTA OFFSET IS A VOLUME-WEIGHTED AVERAGE OF THE OFFSET CHANGES DESIRED ACROSS THE INTERFACE. WITH UNEQUAL CYCCLES, A MATCHING AND RESYNCHRONIZATION TECHNIQUE MIGHT BE EMPLOYED, OR INTERFACING CAN BE ACCOMPLISHED THROUGH A TRANSITION ZONE WHERE THE SIGNALS ARE TRAFFIC-ACTUATED RATHER THAN OPERATED ON ANY SPECIFIC CYCLE. /AUTHOR/