THE SIGNAL BOX
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[ Shared distant signals ]
A number of complications arise with short block sections. The need to offer trains forwards prior to receipt of Train entering section has been discussed in Chapter 2, as has the associated Train approaching bell signal. Another situations where the regulations vary for short block sections is in connection with Blocking back, explained in Chapter 3.
Shared distant signals
Where boxes are close together, the distant for one signal box may not be a sufficient distance from its Home Signal to give sufficient braking distance. There are a number of ways this problem can be overcome.
Taking our example, Box B, the section between B and C is quite short, and C"s Up Distant (below B's Up Home - No.2) is not be the full braking distance from his Up Home signal. Ways of dealing with this can be as follows:
- B"s Up Distant (1) may be slotted by Box C, This means that the signal is controlled by a lever in both boxes, but doesn't actually clear unless both box's levers are pulled.
- B"s Up Distant might be worked in conjunction with an indicator, there was a Regulation (34) prior to 1960 to cover this (known as Distant Indicator Working) but from 1960 the method of working was stated on the Special Instructions for each box concerned. In our example, an indicator (usually a large mechanical device, but sometimes just an electrical indicator) is be provided in Box B behind the lever for his own Up Distant signal. When Box C clears his distant signal, the indicator changes (usually with a loud clunk) to show "Distant Off". Only then is Box B permitted to clear his own distant signal. The indicator is sometimes, but not always, interlocked with the lever to prevent incorrect operation.
- The Western Region had its own Regulation (4A) to cater for these circumstances, which avoided the need for an indicator although the working was not very streamlined. In our example, Charlie at Box C must not accept a train in the normal manner from Bert at Box B unless it has been accepted by the next box ahead of him. If it has not been accepted by that box, Charlie must send the Line clear to clearing point only bell signal 2-2-2 to Bert. Charlie will place his block indicator to Line Clear when Bert acknowledges the 2-2-2 signal. Bert must not clear any signals until the train has passed his distant signal, after which he may do so.