Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 120 of 265
10.2 Red Extension During Interstage
10.2.1 Description
The occupation of an All Red detector loop during its specified stage to stage
movement will generate an All Red extension.
When using priority mode to provide priority facilities for Light Rail Transit schemes,
the priority demands (LRV requests) can be used to extend the all Red period. The
all red extensions called by LRV requests can be configured to be different
depending upon the stage being left (flexible all red).
(N.B. As the extend all red signals are available in special conditioning, the extend
all red period may be introduced due to special conditions when required.)
The extension will continue all the while the loop is occupied. When the loop is
cleared the extension will continue for a fixed period - the All Red Extension period.
When the first phase in the stage that is about to go to green reaches the start of its
red-green transition period, all inter-green times concerned with the interstage will
be ‘held’, i.e. frozen, until either the All Red Extension period or the All Red
Maximum period terminates. Hence the facility is also known as the ‘hold inter-
green’ facility.
The all-red extensions also ‘hold’ gaining phase delays, see section 11.6.
During all modes, except Fixed Time Mode, the red extension and maximum red
period can operate as normal or, if required, the extended red period can be
automatically extended up to the maximum red value.
During Fixed Time Mode, the controller automatically extends the red period up to
the maximum red value for safety reasons.
There are 7 facilities (units 1 to 7) available for different sets of all-red detectors. If
one set were to be used for several stage to stage transitions, this would only
require one facility.
10.2.2 Independent Inter-greens
In some circumstances, when a normal Extend All Red (Hold Inter-green) is applied
to an intersection, some phases are not involved in the conflict and so whose
appearance does not need to be delayed.
In order to cater for this requirement, the Independent Inter-green Facility exists. It is
possible to specify at configuration, for each terminating phase, the inter-greens to
the gaining phases that are not required to be held by the Extend All Red facility.