Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 189 of 265
The ignore move facility is normally only required during modes where it is possible
to have stage change conditions present for more than one stage, i.e. VA, Priority,
Emergency Vehicle and UTC mode.
24.4 Permitted Moves
Permitted moves are not programmed they are achieved by the lack of any stage
movement restrictions.
Although a stage may be prevented from appearing in one mode, there will be
occasions when the stage is active and the mode changes. Moves should therefore
be permitted out of it during the other modes to allow for the stage change
conditions of the new mode.
24.5 Prevented Stages/Phases
The deletion of a stage or phase, which may be achieved by use of the master time
clock, see section 25, may be simulated by preventing them when certain conditions
occur using Special Conditioning Software.
If a stage is prevented it will be omitted from the cycle.
If a real phase is prevented, the signals will remain at red whenever a stage that the
phase normally appears in is active.
If a dummy phase is prevented, any effect its appearance has on stage changes or
timings will be cancelled.
The prevention of stages or phases is effective in all modes except Fixed Time
mode.
Note that phases that are prevented under certain conditions should be configured
as optional phases, see section 6.8. If a fixed phase within a stage is prevented, the
stage is effectively prevented.
24.6 Cross Inhibit Linking
Where two pedestrian crossings are close together, e.g. one across each
carriageway of a dual carriageway, it is often required that both pedestrian phases
do not appear at green together.
‘Cross inhibit linking’ prevents one stream from giving right of way to its pedestrian
phase while another stream has given right of way to its pedestrian phase, forcing
one to follow the other if both are demanded.
This removes the situation where pedestrians that have just crossed one
carriageway also attempt to cross the other carriageway because that pedestrian
phase has not yet returned to ‘no right of way’ (because it also gained right of way
around the same time as the first crossing).