This very important part of the Rule Book addressed what to do when trains were detained on a running line. Most of the time this would be the result of a stop signal at danger causing the driver to bring his train to a stand, whereupon he had to sound his whistle (in semaphore days most signals were well within whistle-hearing distance of a Signalbox). If the train continued to stand at the signal then either the Guard, Shunter or Fireman had to go to the Signalbox and remind the Signalman that there was a train standing at one of his signals and, with one exception, remain in the Signalbox until the train is able to proceed. This had to be done within two minutes of the train being brought to a stand in clear weather, and immediately during fog or falling snow. When in the Signalbox, the Guard, Shunter or Fireman had to write in the Train Register "Rule55", the line on which the train was standing and sign his name against the entry with the time it was made. The Signalman then had to initial the entry. The one exception to remaining in the Signalbox was when the Signalman had devices for the signal levers that served as a reminder that the signals must not be lowered. He had to immediately use these appliances and the man who had gone to the Signalbox had to obtain the Signalman's assurance this had been done, after which he could return to his train.

The same applied when a train or vehicle had passed a stop signal for the purpose of being crossed to another line, or to be let into a siding, or had been shunted on to the opposite running line, or been placed on either a main or branch line at a junction, or when a train or vehicle had been shunted from a siding on to a running line for the purpose of being crossed to another line, then the Guard, Shunter or Fireman had to, when the train or vehicle came to a stand and was detained, proceed immediately to the Signalbox to remind the Signalman of the situation as in the previous paragraph, unless there were printed instructions to the contrary or the train or vehicle were detained at a signal where either a telephone was provided (diagram 1) or where no telephone was provided but where there was track circuiting or electrical depression bars, or possibly Lock and Block signalling in operation (diagram 2). In the event of a telephone being provided, then the Guard, Shunter or Fireman had to telephone the Signalman immediately. The decision as to who had to go to the Signalbox was decided by which part of the train was nearest. In the event of any dispute over this, then it was the Fireman who had to go. In the case of a light engine carrying a Guard and/or a Shunter, then unless they were travelling as passengers (i.e. not on duty) one of them had to go to the Signalbox. In the event of a single-manned (in the driving cab) train being detained, it was down to the Guard or Shunter to go to the Signalbox although where a telephone or a Fireman's Plunger (diagram 3) was provided, the Driver had to make use of such appliance. With a push and pull train with no Guard or Shunter the Driver had to go to the Signalbox if he were at the opposite end of the train from the engine, the Fireman if both men were on the engine.

1. a track circuit or electrical depression bar was provided, as indicated by diagram 2 on or near the signal post,
    
   or
    
2. Lock and Block signalling was in operation
    
   or
    
3. the Driver was in possession of the train staff or electric token on a single line
    
   or
    
4. printed instructions were in operation

it was not necessary for the Guard, Shunter or Fireman to go to the Signalbox, but the whistle had to be sounded. Should the train have been detained for an unusually long period of time, then it was necessary for the Guard, Shunter or Fireman to go to the Signalbox.

When a train was brought to a stand owing to a stop signal being at danger, and a telephone (indicated by the sign shown in diagram 1) was provided then no visit to the Signalbox was required but, instead, the Driver had to telephone the Signalman after waiting two minutes (or such other period as might have been required) to inform him at which signal the train was detained together with the description of his train. If the signal remained at danger then the Driver had to call the Signalman again no more than five minutes after each previous call. Should it have been necessary, due to a failure or other such emergency, for the train to pass the signal concerned at danger then the Signalman had to advise the Driver of the circumstances and instruct him to proceed with caution. As the Driver passed the signal at danger he had to give one long whistle and proceed cautiously as far as the line was clear towards the next stop signal. If the telephone at such a signal was not working, then the Guard, Shunter or Fireman had to visit the Signalbox as if no telephone were provided. It was, however, permissable for the person going to the Signalbox to use another telephone that he might have come across if the distance to the Signalbox would have led to an undue delay. However, he had to make it very clear that he was not speaking from the place where the train was detained and ensure that the Signalman was instructed precisely where the detained train was standing.

This is an abbreviated version of Rule 55, there were other considerations to be observed, for example when shunting and the train stopped halfway past the signal, which was then replaced to danger. However, in the interests of brevity the finer parts of the Rule won't be gone into here.