UTC System Handbook - Siemens

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System Handbook for an STC UTC System 666/HE/16940/000 The "CF" reply bit is used to report a fault in the controller. When the bit is detected by the System a fault is reported. In the UK it is used by MCE 0141 controller to report a fault in its internal fault log and can only be cleared by interrogation of the controller through its local handset facility. 7.3 Master Cycle Counter Under fixed 15 time control the System uses this counter to synchronise all equipment that is on a common cycle time, or multiple of it. The counter is incremented once a second and the remainder after dividing it by the cycle time is the time now in the cycle for that cycle time. This means that controllers with a common cycle time are synchronised, even if they are in different sub-areas. The value is calculated from a fixed reference time and date. 7.4 Relative Priority of Control Methods The System contains a number of control strategies, such as fixed time plans, SCOOT, green waves, Automatic Plan Selection. These may all be requested simultaneously for a junction and a priority system is used to determine which strategy is actually implemented. The System knows which strategies have been requested and implements the highest priority strategy. If this strategy is cancelled then the new highest priority strategy is implemented. The priorities, in descending order are: • green waves • remote requests • operator imposed controller checks (see section 7.14) • operator imposed fixed time control • diversions • timetable imposed controller checks • automatic plan selection • SCOOT 16 • timetable selected fixed time control 7.5 Signal Co-ordination by Fixed Time Plans 7.5.1 Introduction A fixed time plan is a sequence of stage control bits which is repeated until changed by an operator command, or timetable/CAST action. This section describes fixed time plans, in particular the local plan, implementing fixed time plans, preparing the data and making temporary amendments to stage 15 The Master Cycle Counter is not used for controllers under SCOOT control. 16 The System does not differentiate between operator and timetable activated SCOOT control 666-HE-16940-000.doc Issue 31 Page 42
System Handbook for an STC UTC System 666/HE/16940/000 timings and offsets. Also of interest may be the information on green waves in section 7.6, Automatic Plan Selection (APS) in section 7.10, and Diversions in section 8.6. 7.5.2 Fixed time plans Fixed time co-ordination of traffic signals is achieved by using pre-calculated sets of timing for cycle times, splits and offsets at all junctions and pedestrian controllers in the controlled area. The calculation process is carried out remotely from the System using measured traffic volumes, and may be based on the output from a traffic modelling package such as TRANSYT. Several sets of timings are required to deal with different traffic situations, allowing for marked changes in volumes, changes in turning movements and for any tidal flow effects during the day or during special events. Each set of timings is called a "traffic plan" and there are usually separate plans to cover parts of the day such as the morning peak, off peak, evening peak, etc. If necessary the controlled area may be broken up into parts called sub-areas so that different plans can be used in each sub-area. Each plan may not require the control of all equipment in the controlled area or sub-area. In this case the uncontrolled equipment is specified as being under local control. 7.5.3 Local Plan The local plan is known in the System by the number 0. The user cannot configure this plan. If used, then no stage control bits are sent to the selected controllers. 7.5.4 Preparing the data Plan data is stored in files on the System disc. For each item of equipment the plan may define: (1) CONTROL mode For this mode the cycle time and stage start times for each junction controller are defined. For a pedestrian controller the start time of the pedestrian window and its duration are defined. (2) LOCAL In which case the equipment is under local control. (3) Local link inhibit The "LL" bit and no Stage Control bits is sent. (4) Fall back mode Which indicates that the "FM" bit and no Stage Control bits are sent. (5) Part-time signals switched off/on Which indicates that the "SL" bit and no Stage Control bits are sent. The significance of the "SL" bit depends upon the user configured state for part time operation. 666-HE-16940-000.doc Issue 31 Page 43
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UTC System Handbook - Siemens

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