Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 245 of 265
38.2 Red Lamp Monitor
38.2.1 Introduction
To meet UK requirements, the Red Lamp Monitor function is required at part-time
signals (see section 14), at junctions that are fitted with pedestrian audible or tactile
devices (see section 6.2.2) and stand-alone pedestrian signals (see section 6.11).
The vehicle red lamps are monitored and when lamp failures are detected, the
operation of the controller is modified to ensure that unsafe signal conditions do not
occur.
When a first red lamp fails on a vehicle phase, the inter-greens between that phase
and any conflicting pedestrian phases can be increased.
When a second red lamp fails on a vehicle phase (or when no red lamps are
illuminated due to a feeder failure), the conflicting pedestrian phases can be
configured to remain at red and not appear at green (referred to as ‘inhibited’). For
part-time or stand-alone signals, it is a UK requirement that all the signals are
extinguished if two vehicle red lamps fail on a phase.
For Non-UK Controllers, Red Lamp Monitoring can be enabled or disabled as
required, and configured to inhibit, extinguish or flash phases when a second red
lamp failure is confirmed.
38.2.2 First Red Lamp Failures
38.2.2.1 RLM Delays between Conflicting Phases
For each phase to phase transition, a handset alterable time can be defined. These
times define how long a phase should be delayed from appearing when certain
phases terminate with one red lamp missing. These configured times can be altered
using the handset command RLT.
If a time is defined between two conflicting phases, the time can be thought of as an
inter-green extension, i.e. how much longer should the phase gaining right of way
be delayed when the phase leaving right of way has missing red lamps. The usual
inter-green rule applies: if two phases leaving right of way have inter-green times
defined to one phase that is gaining right of way, the phase will appear when both
inter-green times have expired.
In the following diagram, phases A, B and C are losing right of way and the
conflicting phase D is about to appear.
Example 1 shows the normal operation: when all the inter-green times have expired,
phase D appears.
Example 2 shows what happens if phase A has one or more red lamps missing. At
the point where phase D would appear, the RLM facility calculates that an additional