Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 148 of 265
16.2 Facilities
Both Priority and Emergency Vehicle modes have the same facilities unless
otherwise stated. These facilities and timings are listed below and can be accessed
by the handset commands in brackets.
16.2.1 Priority Units (PUT)
A Priority Unit can be regarded as a Priority Channel.
The required phase is allocated to a Priority Unit. The phase can then be regarded
as a Priority Phase. The Priority facilities, e.g. Priority Timings or Priority Inhibits are
set (via the configuration or the handset) for each Priority Unit. This in practice then
affects the times, etc., associated with the Priority Phase.
There are 8 Priority Units available (numbered 0 to 7) which may be divided in any
proportion between Priority and Emergency Vehicle Mode.
If both modes are used, the following conditions are applied:
i) The Priority Units are allocated to Priority mode first.
ii) Emergency Vehicle mode is higher than Priority mode in the mode priority
table.
16.2.2 Priority Phase (PUP)
A Priority Phase is a phase that is equipped with emergency vehicle and/or bus
priority facilities. Each Priority Unit is allocated a Priority Phase.
The Priority Phase may either be a real phase or dummy phase (see example
below) and may either be a phase in general use or used only for the priority facility.
Example: Consider an intersection where the phases overlap two or more stages. It
may be required to demand a particular stage rather than one of the phases in order
to guarantee free movement of the priority vehicle. Therefore, the priority phase
could be configured as a dummy phase that is only configured in the required stage.
16.2.3 Priority Delay (PFD & PSD)
A Priority Delay can be applied to a ‘Priority Input’ such that, when the Priority Input
goes active, it does not apply a Priority demand on the controller until the Priority
Delay Timer has expired. Also see Section 16.8.
16.2.4 Priority Demand (PDE)
A demand for an immediate right of way originating from vehicle(s) equipped to
operate the priority vehicle detection equipment.
A Priority Demand for a Priority Phase is created by either its Priority Unit from an
‘SVD input’ or from the Revertive Priority Demand facility. The priority input may also