Yesterday a runaway engineer's train caused massive disruption to London Underground's Northern Line. There is a BBC report on it here
, but there's so much more to the story than what you can read there.
In order to explain more fully what happened, first I have to give some background and explain a few things about how certain systems work on the Underground.
To begin with, for the record, I used to be a line controller on the District Line, and did half of my training at Baker Street where the north half of the Circle Line, the upper part of the Hammersmith & City and the whole of the Metropolitan Line are controlled from; the Bakerloo Line is run from the control room down the hall from the Met. Both the District & Piccadilly Lines are run from the same room at Earl's Court. The Central Line control room is at White City, and the Northern & Jubilee Lines are run from Cranbourne Street. The East London Line and the Waterloo & City are run by, effectively, glorified signallers - they're not very complex and don't require the special touch of an LC or SDM.
So this whole incident was being monitored from Cranbourne Street by the Northern Line SDMs and signallers - principally the signal operator on the Camden Town desk. Remember this person - they become incredibly important during the story.
Now, the next bit of info concerns the braking systems - and specifically the train protection systems as used on all London Underground trains, with very few exceptions.
Next to each signal, there's a device down on the track called a trainstop; when the signal is red, the trainstop is raised. It's a pneumatic device designed to fail to the up position, just as any failure of a signal results in it turning red.
There is a trainstop and associated signal at each end of a station platform, to govern movement both forward and reverse from that platform.
On the underside of each tube train there is a trip cock; it is connected to the brakes so that if the trip cock hits the trainstop, the brakes are automatically applied and the train stops. There's one at each end of the train as trains can be driven from either end. Like the trainstops, a train's main brakes are operated pneumatically and are designed to fail with the brakes fully on.
Engineer's trains are slightly different; many of them don't run on electricity for a start, being diesel-driven, and not all of them have trip cocks.
Yesterday's incident involved an engineering train that became defective and had to be towed by an out-of-service passenger train. Unfortunately as it was travelling northbound towards Archway, the couplings broke and began to run back down the track towards Camden, out of control and without brakes - they had been isolated so it could be towed, so it ouldn't have stopped even if it had had a trip cock. Thankfully it was just before the start of peak time so the service was spaced out and there were no northbound trains in its path at that point.
One of the handy things about the platforms at Camden is that trains can be reversed from any platform to pretty much any other. So the Camden signaller set up the points so the runaway train would cross from the northbound High Barnet branch platform to the southbound track on the Charing Cross branch (which at that time of the morning would have had fewer trains than the southbound Bank branch).
The SDMs at the same time ordered all southbound trains on the Charing Cross branch to nonstop stations as far as possible until ordered to stop, to increase the distance between them and the runaway train. The driver of the rearmost train also requested all his passengers to move up to the front car, so if the engineer's train caught up to them it would minimise injuries; however due to the prompt actions of the service control staff and the excellent response fro the drivers, the runaway train never came any closer than half a mile to the nearest passenger train.
The track at Warren Street goes up a slight incline on the approach to the southbound platform; this is to slow the forward speed and aid the braking of a train coming into the platform, and it was that incline which halted the engineer's train.
The service was disrupted for quite some time afterwards as the service had to be rerouted through to run only down the Bank branch and up to Edgware, with services on the Charing Cross branch and up to High Barnet suspended until the engineer's train could be safely moved again.
I do hope the signaller, SDMs and drivers concerned all get the commendations they so justly deserve for their quick thinking, professionalism and outstanding teamwork during this incident.