Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 10 Page 85 of 265
Alternatively, it can remain illuminated during the green of its associated phase and
extinguish at the commencement of the amber leaving.
For safety reasons in the U.K., a filter green arrow must always be followed by the
green of its associated phase. To achieve this, a demand dependent filter green
arrow must also demand its associated phase. A filter green arrow that appears
unconditionally must always be followed by its associated phase by means of stage
movement restrictions (see section 24). Alternative methods of control can be
provided to meet other specifications.
During Manual Mode the appearance of the filter green arrow during its associated
stage(s) is configurable, i.e. ON, OFF or Demand Dependant.
See Section 22 for an example of such a green arrow.
6.2.4.2 Indicative Green Arrow
An indicative green arrow may be used when an early cut off facility is required to
allow turning traffic. The green arrow will be illuminated after a pre-determined inter-
green period from the conflicting main movement. This is normally set at 3 seconds
so that the green arrow appears at the start of the conflicting red. The green arrow
will then remain illuminated throughout the rest of the green of its associated phase
and will be extinguished at the commencement of the amber leaving.
If required, the demand for the indicative green arrow will only mature if a demand
exists for an opposing or other specified phase.
It may be required to use a Call/Cancel facility with an indicative green arrow (see
section 8).
For safety reasons in the U.K., the amber leaving of the associated phase must
always follow an indicative green arrow. If a direct move back to the main movement
is required the stage change must go via an All-Red Stage (see section 10.1). This
should be configured as an alternative stage movement (see section 24.2).
Alternative methods of control can be provided to meet other specifications.
See Section 22 for an example of such a green arrow.
6.2.5 Dummy Phase
A dummy phase may be used in situations where timings or detector conditioning
have to be associated with a traffic movement that is not uniquely signalled. The
dummy phase provides suitable time periods or conditions for stage changes even
though no signal aspects are associated with the phase.
Sections 10.1 (all red stage), 16.2.2 (priority phase) and 22.2.3 (green arrows)
include examples of dummy phases.