The fatal rail crash that happened near Abermule in mid-Wales on 26th January 1921, claiming 17 lives, is an example of how disaster can occur when several people make a mistake and each one of them assumes that everyone else is acting correctly. That may sound complicated, but the truth of that statement will become apparent as the story unfolds.
Tablet system for safe single-track running
The rail line in question runs from Shrewsbury to Aberystwyth through the Welsh hills. It is twisty and hilly and single-track. The obvious implication of the latter fact is that two trains must never be allowed to run in opposite directions in the same section. Passing loops are provided at intervals and, by using a “tablet” system, it is possible to ensure that only one train is in a section between passing loops at any one time.
The idea is that the driver collects a tablet at one end of a section and hands it in at the other end (this can be either when the train is stationary or via a collection arm on the outside of a signal box while a train is in motion). This is, therefore, a train’s “passport” for that section.
However, it is not possible for there only to be one tablet for a section, which goes backwards and forwards as trains alternate in direction, because it is often the case that two or more trains need to pass in one direction before one travels the other way. This therefore opens the possibility of a second tablet being issued at one end of a section and the original tablet being issued at the other end for a train travelling the other way, thus opening the way to tragedy should this occur.
The system was made a lot safer by the patenting, in 1878, of the Tyer electric tablet instrument, into which the tablets were placed until such time as they were authorised to be handed to a driver who was due to pass through a single-track section. When a tablet was withdrawn the machines at both ends of a section would be locked until a tablet was replaced in one machine or the other. It was also necessary for a signalman, when accepting a train into his section, to press a release button on his instrument so that the signalman at the other end of the section could withdraw a tablet.
Thus, a train coming the other way could not be issued with a tablet, and neither could a second train going in the same direction as the first enter the section, until the tablet carried by the first train had been placed in the machine at the other end. Each signal box would have two such instruments, covering the sections on either side of it.
In theory, this sounds like a foolproof system, but the events at Abermule were to prove otherwise.
Events at Abermule
On the morning in question two trains were approaching from opposite directions, an express and a stopping train. They were due to cross at Abermule, but the signalman was used to the situation in which one train might run late and the crossing take place at the next station up or down the line, with the aim being to allow the express a clear run by making the stopping train wait for it at either Montgomery (to the northeast) or Newtown (to the southwest), neither station being more than three miles distant. A measure of flexibility was therefore allowable, but the tablet system covered all eventualities.
One unusual feature at Abermule was that the electric instruments were not housed in the signal box but in a room in the station building, and it had become common practice for staff members other than the signalman to operate them. At Abermule there were four staff members, namely the signalman (Jones), a relief stationmaster (Lewis, deputising for the regular stationmaster who was on leave), a porter (Rodgers) and an office boy (Thompson) who performed various duties around the station including collecting tickets from alighting passengers.
Signalman Jones received a signal from Montgomery that the stopping train was about to enter the Montgomery-Abermule section and he duly pressed the release so that the Montgomery signalman could withdraw a tablet to give to the driver. Jones then left the instrument room to return to the signal box to set the road for the approaching stopping train, after he had checked, by phone, the situation regarding the express. This was now in the section on the other side of Newtown, so there was plenty of time for the stopping train to reach Abermule before the express would come through in the opposite direction.
The two junior members of staff had been in the instrument room when Jones accepted the stopping train, and were still there after Lewis the stationmaster arrived back from his lunch and immediately left again to supervise movements in the goods yard. Rodgers and Thompson were therefore the only staff members present when the call came from Newtown to ask for acceptance of the express into the Newtown-Abermule section. It was the porter Rodgers who pressed the button to accept the express, thus allowing Newtown to release the appropriate tablet.
At this stage everything was in order. The stopping train would enter the station and the express would use the passing loop to proceed without stopping as soon as the tablet from Montgomery had been entered in the Montgomery-Abermule instrument, thus allowing the express to collect a tablet as it passed through. In the meantime, both Abermule instruments would remain locked.
Rodgers then left to set the road for the express, for which he needed to attract the attention of signalman Jones, now in his signalbox at the other end of the platform, who needed to unlock the points before Rodgers could move the ground frame lever. Had Jones known that Rodgers was ready to set the points, he would have realised that the express was now in the Newtown-Abermule section. However, before Rodgers could act, the stopping train arrived.
The boy Thompson, who had been with Rodgers when the latter had accepted the express, then crossed the line to collect the Montgomery-Abermule tablet from the driver of the stopping train, now at the platform. He was on his way back to the instrument room when stationmaster Lewis returned from the goods yard. He asked Thompson if he knew where the express was, and the boy told him that it was still the other side of Newtown, running late, despite having watched as Rodgers had accepted it into the Newtown-Abermule section.
Thompson then handed the tablet in his hand to Lewis, as the former had to go and collect tickets from the passengers leaving the platform from the stopping train.
Stationmaster Lewis then made his fatal mistake by assuming that the tablet in question was the one for Abermule-Newtown and that Thompson had collected it for handing to the driver of the stopping train. Lewis would have had no reason for thinking that this tablet would not be available, based on the false information given him by Thompson. He then proceeded to the cab of the stopping train and gave the tablet to the driver, who now assumed that he was free to proceed towards Newtown.
The driver also made a fatal mistake in not checking the tablet that he had been given. Had he done so he would have realised that he was being handed back the tablet that he had only just given to Thompson.
Both signalman Jones and the boy Thompson watched Lewis hand the tablet to the driver, but both assumed that it was the correct tablet. The signals were set and the train pulled away. Rodgers was a bit surprised, but assumed that, in his absence, there had been a change of plan and the express had been held at Newtown for some reason. They all had implicit faith in the Tyer system that guaranteed that a tablet could not be withdrawn from the instrument unless it was safe to do so.
It was only when they reached the instrument room and realised that the system had worked perfectly, but the driver had been given the wrong tablet, that they appreciated what had happened and that they had all, along with the driver of the stopping train, make errors that contributed to a disaster that they were now powerless to prevent.
The two trains collided head on, with the victims including the driver and fireman of the stopping train and fifteen passengers on the express, with many others being injured. The express train driver, despite being injured, searched for and found the two tablets carried by the trains, and one of those was a Montgomery-Abermule tablet that should never have been there.
This was therefore a tragedy caused by the errors of five people who failed to ask the right questions, give the right answers, or have anything but implicit faith in a system that was not so foolproof after all.
As a result of Abermule, changes were made locally so that the instrument machines were moved to the signal box, and nationally so that starting signals could not be pulled until the relevant instrument had been cleared. Fortunately, these measures have prevented a similar accident ever occurring again on the British rail system.
© John Welford