Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 10 Page 77 of 265
5
5
S
S
T
T
A
A
G
G
E
E
S
S
5.1 Facilities
There are up to 32 stages (0 to 31) available for use.
Stage 0 is normally used as a manual all-red facility. It may be used as a traffic
stage.
Stage 1 normally is the start-up stage and must not be deleted.
Some stages may appear in some modes but not others.
Note: Since a change of mode can occur at any time, the controller may temporarily
reside in a stage that is not normally used by the new mode if the controller was in
that stage just prior to the change of mode. The controller can be configured to
leave the stage as soon as possible (i.e. when all minimum green times have
expired) or to leave the stage when normal conditions dictate.
5.2 Allocation of Phases
The available phases are allocated to the stages in any combination subject to the
method of control, the traffic requirements and safety considerations.
5.3 Stages Active
A stage is considered active when all the fixed phases (see section 6.7) that are
allocated to the stage are at green and all phases (fixed or non-fixed) that are not
allocated to the stage are at red.
A stage is considered to be terminating when the first phase which has had ROW
(i.e. been at green) during the stage, loses right of way.
5.4 Interstage Period
The interstage period is the time between one stage terminating and another stage
becoming active.
5.5 Stage Change Algorithm
In all modes, the controller monitors the following every 200ms:
 all demands (for both phases and stages)
 all extensions and maximum green timers
These are monitored in order to check to see if it is possible to move to a new stage,
and serve new demands.
Normally the controller waits until the interstage movement is complete before
looking for a new stage to move to. However, as described in section 39, the “Ripple