IN AN EFFORT TO ADD MORE AND MORE FEATURES (PREEMPTION, MALFUNCTION MANAGEMENT, WEATHER MONITORING, AND DYNAMIC LANE ASSIGNMENT, AMONG OTHERS) TO TRAFFIC SIGNAL SYSTEMS, THE TRAFFIC SIGNAL CABINET HAS BECOME VERY
COMPLICATED (FIGURE 1). FURTHERMORE, NONE OF THE STANDARD FAMILY OF TRAFLIC SIGNAL CONTROLLERS (NEMA, 170, 179, AUD ATMS 2070) HAVE INTERFACES MORE SOPHISTICATED THAN 24-VOLT INPUT/OUTPUT LOGIC. IN FALL 1993, A PROPOSAL
WAS SUBMITTED TO THE TRANSPORTATION RESEARCH BOARD (TRB) INTELLIGENT TRANSPORTATION SYSTEMS (ITS) IDEAS DESERVING EXPLORATORY ANALYSIS (IDEA) PROGRAM TO DEVELOP A DISTRIBUTED INPUT/OUTPUT SUBSYSTEM FOR THIS NEW
CONTROLLER. THAT PROPOSAL DESCRIBED A "DRIVE BY WIRE" DISTRIBUTED CONTROL TECHNOLOGY FOR ELECTRICALLY INTERFACING THE ATMS 2070 TO SENSORS (LOOP DETECTORS) AND ACTUATORS (SIGNAL LAMPS). THE UNIQUE AND NOVEL CHARACTERISTIC OF THIS PROPOSED MODEL WAS THAT ONLY TWO ALTERNATING CURRENT (110VAC) CONDUCTORS WERE REQUIRED TO BE CONNECTED INSTEAD OF THE 100 CONDUCTORS USUALLY CONNECTED TO A NEMA OR 170 CONTROLLER (FIGURE 2). THIS NOVEL INTERFACE WOULD GREATLY REDUCE THE QUANTITY OF WIRING INSTALLED AT TRAFFIC SIGNALS. AGENCIES WOULD SAVE MONEY BY REDUCING LABOR AND MATERIAL COSTS. FURTHERMORE, THIS DISTRIBUTED CONTROL MODEL COULD BE EASILY EXPANDED TO
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