SSR Resignalling

Not quite sure how that can be, as in any manual mode an extra safety envelope is around the train, acceleration is pegged back slightly and movement authority which includes maximum speed are determined by the system.

Might be this that I have mentioned before.

Back eons ago I saw something - fairly unofficial I might add - that compared manual driving guard operated trains on clockwork signalling south of Kennington that suggested a greater TPH than automatic driven OPO crewed trains in auto on TBTC could acheive. All it was was a graph plot albeit a very good one.

It was based on (1) no ATO (2) guard opening doors before the train had actually stopped dead (3) removed need for 42 different computers to agree velocity and acceleration and jerk were zero before releasing doors (4) two persons on the train viewing doors etc for departure (5) 750 V traction and 980 V (or whatever it was) regeneration.

1 2 & 3 all cut dwell time; 4 increased traction acceleration and braking performance.

Repeat, this was *wholly* manual operating under traditional signalling, no ATO at all, and not manual driving (coded manual) under TBTC.


Perhaps someone might be able to work out how the costs of the entire TBTC project and assuming a 40 year book life would compare with employing guards for 40 years on an upgraded recontrolled but not subtantially resignalled track circuit block based Northern line with upgraded traction voltage ?

Having had this post drawn to my attention, I have decided to make a one-off post here, after having drifted away from this forum after finding some of the moderation rather objectionable.

Firstly, on the Jubilee and Northern TBTC the speed and performance profile available to the driver in PM is the same as ATO. Hence there is no practical reason why a driver cannot emulate ATO. Indeed I have reviewed download data which compares identical station-to-station runs in ATO and in PM with a keen driver, and overlaid on each other they were essentially identical. The main difference was the PM profile was slightly rougher due to the driver adjusting the traction/brake controller handle (remember on these trains the handles are optical so are sensitive even to very slight movements of the driver’s hand).

As for bettering ATO performance, there are two ways this is possible. The obvious one is that the Thales ATO has a habit of slowing down too much when e encountering a fall in target speed. So for example if the speed drops from 40 mph to 25 mph the system has a habit of braking down to about 21-22mph, holding there for a few seconds then motoring back up again. As an aside this is one of many reasons why the passenger ride quality isn’t great in ATO. A good driver is able to judge the braking and avoid this. Secondly the ATO attempts to drive at the target speed, however the maximum safe speed is slightly above this, so again it is possible to drive at the MSS in which case the train will be travelling faster than in ATO. The snag is the driver has no indication of what the MSS is, but with trial and occasional error it is quite possible to drive within this margin.

As regards the Central Line, the driving style in coded manual is rather different to TBTC, with much more reliance on actually having to look out of the windscreen. I’m not convinced it’s possible to significantly better the Central Line ATO, but it’s certainly possible to match it. There is one exception, namely that it is technically possible to reach 100kph in CM, whereas ATO will only reach 85kph. So in theory it is possible to better ATO run times where 100kph is achievable. However there is a Rule Book instruction stating that drivers must not exceed 85kph in CM, so this shouldn’t happen. ISTR the brake rate on 92 stock may be slightly higher for ATO than that available to the driver, but in practice if this is so the difference will be so small as to be insignificant.

I don’t have sufficient knowledge of the Victoria Line nor CBTC to comment. I have heard it said that PM on the Victoria Line doesn’t allow full speed, but have not seen this for myself.

That’s all I’m afraid.

I thought that was the case with TBTC but could not remember - it is now about 15 years ago since I was involved with either, and even then this aspect was outside my domain, and all I saw w.r.t. traction was high level powerpoint brainwash fluff.

Imagine then, what could have been done without total resignalling, but with just a 750 V traction upgrade and a recontrolling.

Make that imagination not from the technical viewpoint, but from money - compare the Seltrac resignalling upgrades whole life cost of everything with that of a simpler upgrade retaining renewed track circuits etc.

I did write ...... simpler upgrade retaining renewed track circuits ..... which covers upgrading (i.e. track circuits for altered overlaps) and renewed (which covers life expired assets).

Bit of a sweeping statement. I can vouch for it happening because I have to train people to be able to do it. As for losing time - can't say I have lost anything significant. The system is harsher (comparing it to when I had to learn to drive for assessment purposes on the Central), but you'll still get into BSS or ALD 1 or 2 mins down, which is no different from in ATO anyway.

Nothing for SMA12.
SMA 8 testing 12-14 April 2024.

Which is the next section to be commisioned. Was it FInchley Road to PReston Road? Originally planned for January. Likely before the summer?

What exactly is causing the delay in commissioning this area?

Sacking people clearly isn't the immediate cost-saving excercise it used to be.

Unfortunately it doesn't work like that in the real world.

Some members will know I work very closely with the 4LM team, so I'll try to explain as much as I can without going into specifics...


There are a few factors.

The complexity of the area and the need to interface the CBTC system to the Jubilee Line TBTC and the Neasden Depot signalling systems are one factor. The 12 hour closure in November last year was of critical importance to test some of those interfaces and the commissioning of SMA8 was heavily reliant on the testing evidence that the closure gave. Let's be clear here - this is the most technically complex part of the project.

Secondly, access is a major factor. The last train stables in Neasden depot at 0104 and the first departs at 0435. However, even if the last train finishes on time there is a need to undertake shunting within Neasden depot which at the southern end requires a working signalling system. It's often 2am before staff can start work, and in that time they need to do their work, reinstate the existing system(s) and test them all ready for the start of service the next day. Testing all three systems for handback takes around an hour. So assuming staff don't get access until 0200, they need to test and be off the track by around 0410, and the testing time takes an hour, that leaves around an hour and ten minutes of useable access time.

What about weekends? Doing weekend work in this area requires the suspension of both lines. This is a big ask at the best of times and coupled with the frequency of events at Wembley, means there are very few opportunities to carry out weekend testing. Even if weekends were no object, the fact that we are working with Safety Critical Software means that each software release to fix a problem found in testing (which is inevitable given the complexity of the area) needs to go through a rigorous testing regime before it can be used even with test trains. This cannot be turned around overnight, or else you get Boeing 737 Max 8 style errors. On a non-safety critical (but equally life changing) level, look at the damage poorly produced software in the Post Office's Horizon system caused.

So in a nutshell, the major delays are technical complexity and access to the railway to do work. None of this should be a surprise - I fully expected this section to take a long time based on those factors alone and quite frankly when I was first introduced to how the systems would interact in this area, back in September 2019, it frazzled my brain.


Hardware design is now largely complete and installation is progressing. Software design is still ongoing, in the agreed order, which matches the order of installation/testing progress in other SMAs. Consequently, testing (of any kind) in the remaining District SMAs has not yet commenced. There is little benefit in dropping, for example, SMA13 or 14 software design to commence design of SMA12 software, when SMA12's hardware is still being installed.

So, to answer your question, no - further District line SMAs are not ready.

You might be thinking of the issue last summer (after the 4LM expansion to the east end of the District) when the Control room and trains RMT branch escalated the issue of the number of "Operational restrictions" associated with the 4LM signalling - ie the issues to be fixed by the project/Thales. 

I don't think we need to list the number of ORs, unless it's publicly available. Please consider Rule 7. - Tom

Completion was expected in Q1 22/23 initially, Q4 24/25 a year back, and now slips 9 months to Q3 25/26, i.e. end of 2025.

With the 4LM soon to come to the Met (I know we are still some way off an official completion and service frequency upgrade), do we know if there is a draft or provisional timetable (in tph) expected for the Met line once the new system is fully rolled out?*

If there is not one, what is the general expectation from both those in the know and from those simply speculating?

*I know it may not reach the Uxbridge branch in full at all and this is to remain with the current signalling for the foreseeable.