SSR Resignalling

There is an earlier thread that confirms the date.

What is beyond doubt in the case of the Sub-Surface Railway is that the legacy assets currently used are, by and large, life expired, technologically obsolete and increasingly expensive to maintain and need replacing pronto. What with is an interesting topic given that there are examples on other metro systems around the world that are achieving frequencies in excess of 30 tph with modern form fixed or variable block signalling and manual driving.

As is always the case to achieve high frequencies on these systems, this requires some degree of liberalization of SPAD policy. To be honest, that kind of reliance on humans would be seen as a backwards step by some (politicians and industry players alike). This is in spite of the fact that major failures with ATO can and do happen which highlights the importance of safety critical staffing on trains whether they be automated or not. It must be said though, the trend is firmly now in moving towards computerised based signalling solutions where possible. The digital railway is a product of the times we live in.

I am personally skeptical whether 4LM will be capable of consistently achieving the maximum frequencies being proposed. SelTrac was never intended for use on systems more complex than airport people movers such as the Victoria line. Yet we have an ongoing deployment on arguably the most complicated parts of a brownfield metro system in the world. The SSR is in for an interesting few years!

The S7's currently have a top speed or 48, (I think) mph this could be altered up or down, the same goes for the S8's.

No exactly the standards of 100 years ago would not be permitted today! The issue of dwell time cannot be understated. There are statistically more passengers today and even with more frequent services, modern signalling and faster trains, one of the limiting factors will be the speed at which passengers can board and alight from the train. Unless humans can evolve somehow to overcome this, there will always be a realistic limit.

Another factor is that passengers who take longer to board (e.g. those with mobility issues) were simply not able to travel, unlike today. (Accessibility and inclusivity is a Good Thing overall, even if it does increase dwell time a little).

I suspect it's probably linked to the size of signalling overlaps somewhere. If the signalling was designed for trains with a certain maximum speed, then the new trains are probably capped to match - especially given that new signalling is appearing over the horizon.

I see no reason why this should not be increased once ATO is operating across the network, I have no idea if it is going to happen.

I am not sure if that was meant to be sarcastic or not but I didn't say standing space is apple and sitting space is orange here lol...anyways I think we should move back to the topic?

Im guessing Euston Square to King's Cross, King's Cross to Farringdon, Victoria to Sloane Square and St. James's Park to Victoria. SMA 5 could have Sloane Square to South Kensington having better speeds.

Yes, the new Watford South Junction is pants compared with the former alignment but it does allow a faster curve on the local line to Watford.

Anyway I digress......

Perhaps speed limits were breached - not being a train driver I cannot really comment.

But, if this was happening then what is significant is that it was done in perfect safety - therefore since the speeds which might have been being travelled at were proven 'safe' they should become the normal limits. Especially since train speeds nowadays are very tightly monitored and controlled with automated systems preventing breaching the limits.

As an aside, I was on the SSR today and noted that the trains seem to accelerate more rapidly than before, but they were running so close to each other that it was not possible to experience the newer top speeds (where they exist).

Whilst waiting on the platform at Kings Cross (eastbound) the trains seemed to be entering the station more slowly than before and there was at least one train where the white lights did not illuminate immediately prior to door closure. However that may have been my fault (LOL) because it only happened when I had a still image camera in my hand hoping to film the white lights in action!

I also noted that the new track to the east of Tower Hill's bay platform is still not available for use.

Whether it was done in perfect safety is a matter for debate. It’s worth remembering that the Central Line had a collision at Holborn in 1980 where the design of the signalling was insufficient to prevent a collision occurring after a signal aspect was disregarded.

The traditional LU signalling was superb, and over the years standards changed to design out more and more of the few holes which did exist in it. But it should never be regarded as infallible - sooner or later a combination of circumstances could occur where someone finds a route through all the layers of protection built in, or something happens which simply no one had thought of (eg Moorgate).

Yes liberal interpretations of speed limits was rife as recently as the 1990s. Likewise the speed limits themselves were less scientific than today. However the philosophy tended to be that things were designed on the basis that you needed a few things to go wrong in order for an accident to happen - so perhaps a driver going a little bit faster than the limit, train with slightly weak brakes, a tired driver, an overlap not to modern standards, a train stopped in an unusual place, and perhaps even more besides.

One could quite reasonably argue that the level of risk was sufficiently minimal to be acceptable, especially if the trade-off was faster journey times, or perhaps more usefully greater throughout of trains on a crowded railway. So a tolerable level of safety quite probably (LT had an excellent safety record for sure and collisions between trains under normal working have been rare as hens teeth), but I’m not sure one could go quite as far as to say perfect safety.

Having said all that, I do share an element of frustration that we do struggle nowadays to match some of what was done in the past, either in terms of journey time or throughput of trains. Credit is very much due to the Victoria Line Upgrade project for actually managing to design and commission something genuinely impressive, that seems to actually give as a good taste of past wonders, but with modern levels of safety / risk management at the same time.

As a footnote, it’s also worth adding that dwell times are a factor too. Firstly there’s simply more passengers than in the past, which doesn’t help. There’s also things like mobility impaired passengers who in the past had to be very committed to dare try using the system. Thirdly guard operation of doors was probably a bit quicker than driver operation (with a good guard anyway!), and of course perhaps controversially it’s fair to say there wasn’t quite as much focus on platform/train interface safety, and if there was there was less CCTV so being brutally realistic if something did happen it was less likely to result in a manslaughter charge. Where we don’t help ourselves today is with systems like TBTC wasting a couple of seconds before the driver can open the doors, something again the Victoria Line managed to not have.

It's got to be remembered that at the time, the majority of Amersham services ran fast along the main lines, so the realignment to give a faster curve on the local made sense, as the most benefit was provided to the traffic patterns of the day. Unfortunately a year later that all changed...


Yes, but there were significantly fewer trains in those days, both due to a lower demand and a shortage of stock or crews (or sometimes both). With lower demand and fewer trains running around there are less opportunities for delay and less need for recovery time.

The introduction of the various Migration Areas are linked to potential improvement in JTC (Journey Time capability - nothing like an old PPP acronym one in a while), once SMA5 goes in I expect we will see a timetable change on the SSR taking advantage of the performance improvements that CBTC offers.