SSR Resignalling

Great Portland Street - Baker Street is indeed within a commissioned CBTC area, specifically Signal Migration Area (SMA) 2 which went live in September 2019. CBTC has in part facilitated the removal of performance caps on the S stock but these benefits will only start making major differences as more areas get commissioned.

One of the major gripes I have with CBTC on the S stock is how it motors up when creeping behind a train that is just leaving a station platform. The system motors up rapidly before suddenly switching to a coasting vector then back to motoring which creates a series of horrendous jolts. I think this is more of a Thales product issue because the Jubilee 96 and Northern 95 stocks suffer the same issue with the earlier TBTC but it’s still quite annoying.

Wikipedia lists the S stock acceleration as 1.3m/s^2, same as the 2009 stock, but the latter feels much faster, even on CBTC sections.

Is the full acceleration actually being used anywhere yet, or have the trains I've been on just been too punctual and therefore going slower?

Quite apart from time seen as wasted between stations, I'd like to see the ATO final 'flare' to a stand improved and CSDE asserted as soon as the train stops. There's at least 2 seconds wasted every stop on these. 2 seconds per stop is 84 seconds lost from Ealing Broadway to Upminster. Not far short of a minute and a half...
Compare this with the flare, stop and door release on Central and Victoria lines to see what I mean. No messing, the train arrives, stops and the doors open, no real delays.
I can remember being really worried about up to 300ms to get the S stock's pre-ATC CSDE to act. Turns out to be as nothing by comparison!

It is still possible in non-CBTC areas

Any major obstacles or challenges uncovered during this latest testing?

They definitely couldn’t test everything thanks to fleet at Lillie Bridge Depot

I hope they sort out Moorgate - Liverpool St. That is annoyingly slow for the past 2 years. I cannot understand what the point is of the train practically coasting between these two stations, when in the opposite direction it leaves at normal speed and does not do anything like this.

My memory is that the gradients weren't particularly noticeable; I've walked it (albeit several years ago now) and didn't notice it being particularly steep.
That section is always likely to be slow however, if there's not a queue forming behind a train trying to cross Aldgate East Junction there will be one forming behind a train trying to cross Minories Junction or get into Aldgate platforms. The other direction is faster because trains are going away from the junctions where the queues are forming.

The speed 20mph restriction was introduced prior to ato, I heard at the time both that it had been introduced for clearance reasons and because of signal sighting, signal sighting was bad, on the inner home into Liverpool St.

If signal sighting then no need for it the still be there and if for clearance then that is also confusing as A stock was wider than S stock so ?

On the subject of Moorgate > Liverpool Street, might I offer a speculative comment.

EB the [paper] WTT running time is variously 1.75 2 2.25 min, depending which actual service you look at, but WB it is always [well all those I looked at] 1.5 min.

WB is timetabled shorter timed run than EB => so WB needs smarter running to maintain timetable, but EB maybe if things are early coasting etc eeking out the run time to regulate time before Aldgate to mitigate junction conflicts (includes into the terminal platforms).

With a short run like this, even 15 sec imbalance would be noticeable, i.e. difference between 1.5 min WB and 1.75 min EB, and then the difference between 1.5 min WB and 2.25 EB min is huge.

I could possibly go look up the run times in the signal control data on the timetable servers but I suspect that won't produce anything different when rounding to the nearest 15 sec interval.

Perhaps the question is ''why is it timetabled like this'' rather than ''why do EB trains totter and WB do not''.

Repeat, I am speculating here.

Completely agree, although there are sections where I do wonder if trains will travel quick or take off much quicker. One thing which still annoys me is that SB Met line trains departing finchely Road which are now under CBTC, dont do more than 10-15mph immediately after departing until they get around to well after the crossover area. Pre re-signalling, trains tooks off at full speed (or whatever the limit was). I cannot understand why its so slow now, even for trains which are running late.

On the other hand, NB met trains departing Finchley road are still doing so under manual driving and to this day, cannot match the acceleration of the jubilee line trains next to them. I expected this under the A stock and in the early days of the S stock when performance was set to match the A stock, but the S stock is much newer than the 96 stock and no longer has performance limited to this extent. I wonder if they will match the acceleration of the 96's once this goes over to CBTC?

On the parts of the sub-surface railway with the old signalling, the train performance was capped to that of the old trains. This was also true on Central, Jubilee and Northern lines prior to the signalling upgrades. The reason is that on LU, signalling design and train performance go hand in hand*. The only exception that I recall is the 2009 stock on the Victoria line where the new trains were introduced with their full performance whilst the old trains remained**. That was allowed because the new ATP/ATO on the new trains took account of the higher performance, whilst the old trains continued at their somewhat more pedestrian pace.

* a short answer with more complexity than I can go into here
** another short answer with an even more complex long version!

Jimbo, I suspect that if you were correct then some trains would move through the area quickly, which does not happen.

I still feel that the reason for the slow speed is for the same reason as the 20mph speed limit which was there before ATO, though I don't really know why that restriction was introduced in the first place.

Ultimately the maximum speed limits set up within the CBTC system are provided to Thales by the track engineers responsible for the given section. It seems that the speed limits given to Thales can vary from what they were under the legacy signalling system.

Now it depends how look at it but for starters the signalling system will determine the ultimate capacity of a given piece of track. The factors involved, at least when it comes to the legacy system are a combination of things like the max weight, max length and max speed of trains (ie, how fast they can actually go rather than the signed speed restriction) plus gradients, curves, etc. So the capacity of the legacy signalling system notwithstanding the curves, gradients, points, platforms, etc would likely naturally determine some of the signed speed limits and drivers drive accordingly.

CBTC on the other hand, being moving block, presumably needs to be told its speed limits in a more controlled manner as by the very nature of the CBTC signalling system itself it doesn't naturally determine the speed limits in the same way that a fixed block legacy signalling system does. Dunno if that makes sense to you, the reader, but I know what I mean even if I'm not making sense to anyone else!

Anyway, we have a similar oddity on the District approaching Embankment w/b where under the legacy system we ran over the crossover and into the platform at line speed (35mph) whereas under the CBTC signalling system the train slows to 20mph. No rhyme or reason as to why!

EDIT: I suppose what I was trying to say in my original ramble above is that the two different systems of control can’t be directly compared because they are just that; different systems of control. It’s like comparing apples and pears. They’re both green and they’re both fruits but they’re equally very different green fruits.