Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 10 Page 78 of 265
Change Facility” allows the controller to look for a new stage while the controller is
still moving between two stages.
In order to select the next stage, the “SUGGESTED STAGE”, the controller goes
through the following decision-making process.
Firstly, the controller sets the “suggested stage” as the current stage and the
number of new “phases & stages to get right of way” to ‘none’. These two items will
then be updated as the controller goes though its decision-making process.
The following process is performed for each stage in cyclic order starting at current
stage +1. Stages not allocated to the same stream (see section 5.6) are ignored.
A worked example is given in section 22.1 “A Vehicle Actuated Example”.
1. Are any of the fixed phases in the stage or the stage itself prevented and/or
deleted?
If NO, proceed to next step.
If YES, (i.e. prevented and/or deleted) try the next stage in cyclic order
(starting at step 1).
2. Are there demands for phases in this stage or for the stage itself?
If YES, proceed to next step.
If NO, (i.e. phases/stage not demanded) try the next stage in cyclic order
(starting at step 1).
3. Can the current stage be terminated, e.g. will all phases which have
extensions (and for which the maximum green timer has not expired) or have
minimum green times running, keep right of way in this stage?
If YES, proceed to next step.
If NO, add the demanded phases in this stage (or the stage itself if stage is
demanded) to “Phases & Stages to Get right of way” (for checking later).
Then try the next stage in cyclic order (starting at Step 1).
4. Will all demanded phases which appeared in previously checked stages and
any specifically demanded stages previously checked (i.e. “Phases & Stages
to Get right of way”) get right of way, i.e. be serviced by this stage?
(N.B. Obviously if a previously checked stage is itself specifically demanded,
no other stage can satisfy the demand and the answer to the above question
will be NO. Stage demands are normally only inserted from special
conditioning or modes of operation where specific stages are requested, i.e.
CLF, UTC, Hurry Call, Fixed Time, Manual or Manual Step-On.)
If YES, proceed to next step.