Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 129 of 265
If when Fixed Time, CLF, VA or Manual has been selected, it is not a higher priority
than the current mode, no change of mode will occur.
EMERGENCY VEHICLE, HURRY CALL(S) and PRIORITY modes must always have
a higher priority than VEHICLE ACTUATED mode (or FIXED TIME mode if there is
no VEHICLE ACTUATED mode) but their priority above other modes is dependent
on the required method of control of the intersection.
Several different stage change conditions for different modes may be active at the
same time, but the controller will only respond to the ones of the highest priority
mode. When a change of mode occurs, the controller will respond to the current
stage change conditions of the new mode. For example, during UTC mode a CLF
plan will continue to run with the group influences having no effect. When the mode
changes to CLF the current group influences will become effective.
The changing of modes cannot override minimum green and inter-green timings.
Note: The controller must never be without a mode requested. Therefore, either VA
or Fixed Time must always be configured in the mode priority.