Specifications

ST900 Family General Handbook

667/HB/32900/000 Issue 11 Page 119 of 265

There are three methods of achieving an all-red display:

 By using an ‘all-red’ stage.

 By using the ‘extend all-red’ facility.

 By using ‘on-crossing detectors’ on a near side pedestrian phase.

An All-Red Stage is a stage during which all signal phases are ‘at no right of way’

and thus display their red signal aspects. This is covered in section 10.1.

The ‘extend all-red’ facility can extend the all-red condition between conflicting

phases in certain stage to stage transitions up to a pre-determined maximum. This is

covered in section 10.2.

Section 7.3.4 describes ‘on-crossing detectors’ that can be configured to extend the

clearance period to all conflicting vehicle phases while pedestrians continue to

cross. With ‘near sided signalled pedestrian crossings’ this extends the pedestrian

red / vehicle red period as described in section 6.11.3.

10.1 All-Red Stage

The All-Red Stage can be called automatically and used to provide a ‘buffer stage’

between conflicting phases, e.g. as shuttle working on bridges or on moves from an

indicative green arrow turning movement back to the main movement.

The All-Red Stage can have a minimum period that can be extended by the relevant

detectors up to a maximum period. This is achieved by allocating a dummy phase to

the stage to provide a minimum green, green extension and maximum green. But

note that during modes other than Vehicle Actuated, All-Red Stages will not

normally be extended, they will just be displayed for the minimum period, unless

special conditioning is used.

Caution: if Stage 0 is as the alternative move for changes to stages other than Stage

1, problems can arise since the controller will decide on stage changes cyclically

and thus naturally consider demands for stage 1, stage 2, etc, in order, regardless

of which stage started the move.

However, any of the stages available, including Stage 0, can be considered as an

All-Red Stage. Thus for shuttle working on bridges for example, stages 1 and 3

would provide the two traffic flows and stages 0 and 2 would provide the ‘buffer’ All-

Red Stages.