WHAT IS A CLOSED LOOP SYSTEM?

A "closed loop system" is a system of communication between individual signalized intersections within an arterial or a network of arterial roadways and the Traffic Engineer.

A closed loop system basically consists of sampling detectors at intersections, local controllers, one or more on-street master controllers and a central microcomputer.

The system is called "closed loop" because two-way communication can be maintained between the street controllers and the user. "Open loop" systems maintain only one-way communication "up" from the sampling detectors to the on-street master to the local controllers, but no feedback is received from the local controller or the master. The addition of the central microcomputer "closed loop" in the system’s communications. Data is transferred from the sampling detectors to the master via the local controllers; the sampling detectors report to the central microcomputer via the master; and the central microcomputer transmits information to the master and to the local controllers via the master.Data Loading

    The following data is entered by the microcomputer user via a keyboard:

  • Controller settings such as minimum and maximum GREEN, YELLOW and RED times
  • System timing parameters such as cycle lengths, offsets, splits and permissive periods
  • Traffic responsive computation information such as sampling detector threshold values, detector assignments and weighting factors
  • Time clock information (at the master and local controllers) and Time Of Day (TOD) and Day Of Week (DOW) schedule entries

    • The microcomputer "downloads" the above data to the master controller and to each local controller via the master. 


                                                                     System Monitoring and Reports

    The central microcomputer can receive from the master the following information:

    Mode of operation (TOD/DOW, traffic responsive, free, etc.) for the current time and/or previous 24 hour period.

    Status of local controllers (flash, preemption, failures, etc.) for the previous 24 hours.

    Status of sampling detectors (in/out service, failures) including all volume and occupancy data for the previous 24 hours.