Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 246 of 265
3-second delay is required. Even if phases B and C also had missing red lamps, the
calculation would still result in a 3-second delay.
Example 3 shows what happens if phase A has no missing red lamps, but phase C
has one or more missing. At the point at which phase D would normally appear, the
RLM facility calculates that of the 5 second delay required by phase C, only 2
seconds is left to run. Therefore, phase D is delayed by 2 seconds. Even if phase B
had missing red lamps, the RLM facility would calculate that only 1 second of its
delay is left to run, which is less than the delay required by phase C.
Phase D
Phase A
Phase B
Phase C
Phase D
3s
Phase D
2s
Example 1
Example 2
Example 3
IGN=6s RLT=3s
IGN=6s
RLT=3s IGN=4s
RLT=5s
Inter-greens:
A B C D RLM times: A B C D
A - - 6 Required delays A - - 3
B - - 4 when this phase B - - 3
C - - 6 terminates with C - - 5
D - - - missing reds D - - -
Figure 41 – First Red Lamp Failure Delays (Example 1)
38.2.2.2 RLM Delays between Non-Conflicting Phases
For most junctions, delays are only required between conflicting phases. However, it
is sometimes required to delay a number of phases simultaneously so that they
always appear together.
To get two phases to appear at green at the same time on a certain stage to stage
movement, the phase that would otherwise appear first is delayed using phase
delays (see section 11.3). Following a single red lamp failure where one of these
phases is delayed, it is sometimes required that the other must also be delayed,
even if it does not conflict with the phase which has missing red lamps.
Therefore, a red lamp monitor delay time can be specified between two phases that
do not conflict. In this case, this time is used directly to delay the phase that is
appearing, since there is no inter-green between two such phases.