Why no bi-directional running?

Probably because it would confuse punters if an Eastbound train arrived on their Westbound platform and vice versa. You know what people with earphones are like...

Reverse running was done on the Victoria Line, I remember as a child their was a problem with the service and we were told to go to the Southbound platform to catch our Northbound train. Can't remember the station, year etc. I'm afraid.

Platform 2 on the Central Line at Leytonstone offers trains in both directions and there are probably a few other stations which do this.

Cost of signs too would be a factor.

Bi-directional running occurs at East Croydon. ("Next stop Brighton" can be the case on two of the usual London bound platforms) It has taught PAX to read the platform indicators before they board - it would be a new skill for some Londoners.

It was designed out of the Jubs new signalling at extra expense, allegedly because Tube Lines were not specifically asked for it.

Isn't bi-di helpful if a train cant move itself under its own power and a train can be summoned to help pull or push it along to the nearest siding?

For the Jubilee, surely bi-di Stratford to Waterloo would have been useful - there are enough cross-overs to turn trains around, Waterloo, London Bridge, Canary Wharf, North Greenwich and West Ham through to Stratford. I think there is a bit of bi-di West Ham to Stratford as I was on a Jubilee train which crossed over near the staff halt onto the Eastbound and then a train on the normal approach went into platform 13 and the train I was on went into 15 at the same time! Weird having two trains race into Stratford in the same direction alongside each other.

Pardon my sense of humour but how else can trains run but between stations?

That's due to the siding at one end and two trailing crossovers at the other (one for each branch)

When you say Jubilee is bi-di, I think that is rather exaggerating the meaning! A small bit of bi-di in and out of terminal platforms and depots is hardly what we are talking about here.

Jubilee is NOT bi-di anymore than any other underground line at present.

DLR is fully bi-di - this is what this thread was getting at, and in particular why a system such at that installed on Jubilee (i.e. virtually the same as DLR) why is wasn't just put in with bi-di.

With SSR - is that going to be fully bi-di in the true sense, or just 'terminus and turnbacks' like the Jubilee and other lines

If the running line is bi-di you wouldn't be going the wrong way!
Maybe signage would be a little confusing but DMIs could be accurate. It would mainly be useful during service disruptions.

In 2005 the jubilee ran single line on a weekend or two between Kingsbury and Stanmore to allow a service to continue whilst Wembley Park was being refurbished. This meant a service could still be run without forcing everyone onto rail replacement buses. This would obviously not been possible under the current system.

It was done under 'trains locked in' - there's a post somewhere on the Forum that I wrote up about it - I have a copy of the TTN too.

I think that there's absolutely nothing stopping this repeating itself, apart from the fact that a) the procedure probably hasn't been written and b) there would need to be some temporary bang road stopping marks. It'd be rather slow though, I should imagine.

With the correct clipping, scotching and PNX/other protection malarkey the two trains could run in complete safety - remember these are two trains, each captive on their own line.

Bi directionality is useful if there is a problem on the line.
A couple of recent experiences of mine on the DLR illustrate to illustrate this.

There was a failed train (I think) between Cyprus and Gallions Reach. Trains from the west ran as normal into the westbound platform at Prince Regent and then reversed back east, crossing over to the westbound line between there and Custom House. Meanwhile a single-train shuttle service was running on the westbound line between Prince Regent and Cyprus. No points needed to be clipped or scotched, and it didn't take long to set up.

Approaching the end of service one night, there was a queue of three or four eastbound trains waiting to get into Gallions Reach (the delay being caused by the length of time it takes to ensure the train is empty before heading to the depot). So the ex-Stratford International train I was on that was heading for Beckton ran wrong road from Prince Regent through to Beckton, bypassing the queue at Gallions. There were no westbound trains in the way (if there were any more that night, they were in the queue or already west of Prince Regent).

The flexibility to do things like this is the benefit of bi-directional signalling.

So, if anyone would be prepared to stomache another lengthy round of closures, it would be possible to fully commission such a feature, instead of letting it lay 'dormant'? Thats interesting as Mike Brown in an address to the assembleys transport comittee gave an extremely stong impression that the whole ability was removed at extra expense from the default options...

I could not agree more it would be daft to have single line working over an section this would just cause delays and would slow the line down.