And that the investigation will be wide ranging even asking why wasn't the line upgraded to,double track
I imagine that one's quite easy - not enough traffic to justify the cost.
I must admit I do find it quite shocking that we have had two collisions with heavy loss of life within a relatively short period, both in developed, wealthy European countries where it appears that a major causal factor was an over reliance on procedural controls when the susceptibility of humans to make errors has been recognised for longer than anybody on the board has been alive.
Though they do seem to have been under very different signalling systems. If I recall correctly, the German system was heavily interlocked and failsafe. But when it did fail safe there was a manual over-ride with little in the way of protection from mistakes.
They were so used in the US - the results often known as "cornfield meets". Not really that safe - fair amount of literature knocking around on the subject.
According to Wikipedia, the Long Island Railroad (a primarily passenger railway) still uses train orders at the extremities of the system. Track Warrant systems in which permission to enter a section of track is given by radio are still common in North America. This sounds scary to someone used to British signalling, in that it relies completely on the driver correctly stopping at the end of the permitted area (which could just be a milepost) with no override if they fail to do so. It seems to work reasonably well, though of course for far less intensive services than we are used to in the UK. In a sense it's a voice based version of RETB, but cheaper and with much more flexibility. Just less safety.
Some years ago there was a freight line in New York state which ran a passenger shuttle service in the town at one end of the line (I think in return for tax breaks). When I travelled on it and the driver realised I was just along for the ride he invited me into the cab, at which point I discovered that as well as the driver he was also the dispatcher, controlling not only his train but a passing freight train.
It was Abermule that resulted in the Section signals being interlocked with the Token.
Also remember that the token cannot be released unless there are no tokens "out" and that release requires the permission of BOTH signalmen to obtain.
With "modern" variations such as no signalman key token, and no-signalman token remote (which according to what I have just read on the web is, like RETB, is not interlocked with signalling but (also like RETB) now has TPWS protection.)
Also human voice communication is one of the worst ways of communicating safety critical information - it's one of the big advantages of bell codes - the phrases are predefined and thus cannot be corrupted by persons 'add lobbing'*
* you try and read from a script to an audience without putting your own spin on it - it's not as easy as you think.
I'm not convinced by that. I think the success of modern air traffic control shows that voice communication can be perfectly fine with the appropriate procedures and training.
Likewise the North American track warrant system I referred to above. (There are various web sites around that let you listen to this going on).
I think if you replaced bells by a properly defined set of messages "class x train entered section" it would work just as safely. Bells presumably do have the advantage that you don't have to wear headphones or stop what you're doing to lift up a phone receiver to hear a voice message clearly.
With NSTR, don't the drivers communicate with the signaller by phone rather than bells?