Recliner wrote:
Clive D.W. Feather wrote:
In article , writes
Don't know if this has already been posted:

https://www.dailymail.co.uk/news/art...nched-commuter
-train-going-wrong-way-London-Tube-line-nearly-crashes.html

How on earth can this happen?

Possibilities based on what I can see:

(1) Met train is heading for Chesham, the points are therefore set to
cross over, and the Chiltern train SPADed.

Looking at more pics, I'm leaning more to this theory. The trains seem to
have almost met when the Met train was standing at the C&L platform, so it
must have been an eastbound Chiltern train meeting a westbound Met train,
probably heading for Chesham. So the Chiltern train must have run through
and damaged the trailing points set for the Chesham branch.

But why didn't the tripcocks stop it well before then? Was it a signalling
fault, rather than a SPaD?



I think the Met train was eastbound, and the Chiltern train heading for
Amersham, but was wrongly put on the crossover to the eastbound line.
That's the route taken by Met trains to Chesham, and no Chiltern train
should normally go that way.


(2) Previous train through the area was a Met train to Chesham, the
points haven't been moved since, and the Chiltern train SPADed.

I doubt it. The tripcock would have stopped it, even if the Chiltern driver
went through a red light at low speed.


(3) Either of (1) or (2) but a wrong-side signalling failure meant the
Chiltern train got a green signal.

Yes, possibly, the Chiltern got a green signal that would take it across
the crossover. But that's at least two failures, as that route should never
be set for a Chiltern train, and the signal should have been at red even
for a Met train heading for the crossover, given that it took it straight
towards an eastbound Met train.


(4) Either of (1) or (2) but the signaller authorized the Chiltern
driver to pass the signal at danger.

Why would a signaller authorize a Chiltern train to take the route to
Chesham, regardless of the signal?


(5) Repeat of Farnley Junction: a wiring fault meant the normal and
reverse positions of a crossover were exchanged in the signalling.

Wouldn't such a permanent fault have shown up much earlier?


(6) Repeat of Barnham: an earth fault meant the points moved as the
train approached them.

That sounds more likely. It's probably why the Chesham branch stayed closed
for a couple of days, while the points and all the wiring was carefully
checked.


I'm sure there are more possibilities. We'll have to wait and see what
the RAIB have to say.

Surely the chiltern driver knew what side of the
line he was on?

The crossover is close to the station, IIRC, so he would have gone into
emergency braking as soon as he either saw the points facing the wrong
way or when he realized he was on the crossover. Don't forget trains
take some distance to stop.

Yes, and having just left the C&L station, the train wouldn't have been
travelling very fast.