BBC News - DLR trains too speedy so engineers slow them down

[NorthLondoner]

http://redirect.viglink.com/?key=71...ttps://www.bbc.com/news/articles/c4gqgg9q2dro

Speed restrictions have been introduced on the automated Docklands Light Railway (DLR), after engineers discovered the trains were going too fast on some sections of track.

TfL’s general manager for the DLR, Tom Page said: "Following a review of our signalling system we identified a pre-existing technical issue, which meant there were a number of places where there is not enough margin between maximum recommended speed and the speed of the trains.

 

[MCR247]

I saw this article earlier and thought it was a bit of an odd headline. It makes it sound like trains were going over the speed limit/running speed, when from my understanding, all that has happened is speed limits have been reduced on parts of the network after maintenance teams checked some things.

 

[Trackman]

I saw this article earlier and thought it was a bit of an odd headline. It makes it sound like trains were going over the speed limit/running speed, when from my understanding, all that has happened is speed limits have been reduced on parts of the network after maintenance teams checked some things.

I thought that, it's as if they have slowed down the whole network. It's badly written.

 

[boiledbeans2]

[...] all that has happened is speed limits have been reduced on parts of the network after maintenance teams checked some things.

From my understanding of that article, the speeds limit reductions are permanent?

The article mentions:

TfL’s general manager for the DLR, Tom Page said: "Following a review of our signalling system we identified a pre-existing technical issue, which meant there were a number of places where there is not enough margin between maximum recommended speed and the speed of the trains.

According to wiki, the DLR uses a SelTrac signalling system from 1994. So does it mean that the speeds limits have always been too high since 1994?

 

[Peter Mugridge]

According to wiki, the DLR uses a SelTrac signalling system from 1994. So does it mean that the speeds limits have always been too high since 1994?

I suspect it's more likely that larger safety margins have been recently put in place meaning that the previous speed profiles no longer comply?

 

[MCR247]

From my understanding of that article, the speeds limit reductions are permanent?

The article mentions:

According to wiki, the DLR uses a SelTrac signalling system from 1994. So does it mean that the speeds limits have always been too high since 1994?

Whether permanent or temporary, my point was more that (imo) by saying the trains were going too fast the article implies that the train is at fault. For example, if the speed limit is 30 but trains were going at 35 in reality. But, from my understanding, what’s happened is that it has been realised that the speed limit was too high and it has been reduced accordingly.

 

[bramling]

Whether permanent or temporary, my point was more that (imo) by saying the trains were going too fast the article implies that the train is at fault. For example, if the speed limit is 30 but trains were going at 35 in reality. But, from my understanding, what’s happened is that it has been realised that the speed limit was too high and it has been reduced accordingly.

I have a feeling this is likely to be more signalling related, and is possibly something that has been identified as part of the preparations for the new trains.

 

[vinnym70]

Signs up today regarding withdrawal of Lewisham - Stratford direct trains which feel like they've only really just been reinstated.
The service feels like it has more uneven gaps now, more so than I can recall of late but I'm not sure if that's directly related.

 

[Harpo]

Signs up today regarding withdrawal of Lewisham - Stratford direct trains

I remember how amazed I was by some 1 (yes - one) minute DLR turnrounds at Lewisham in the past. If they still happen I can see how easily a small speed restriction could have an impact.

 

[DGP]

From a short trip yesterday, I noted that two places where speed restrictions had been introduced was on the south bound approach to South Quay Station (where the track crosses from the north to the south side of Marsh Wall) and then after leaving South Quay, on the the sharp 90 deg turn towards Crossharbour. Has anyone spotted others?

It does seem strange though since these are original parts of the DLR and trains have been running at those speeds over those places since 1987.

 

[Harpo]

I noted that two places where speed restrictions had been introduced was on the south bound approach to South Quay Station (where the track crosses from the north to the south side of Marsh Wall) and then after leaving South Quay, on the the sharp 90 deg turn towards Crossharbour.

Interesting observation. The Lewisham extension has had issues in the past with deterioration of ferrules (where track fixings are bolted into concrete) on small radius sections.

 

[DGP]

Interesting observation. The Lewisham extension has had issues in the past with deterioration of ferrules (where track fixings are bolted into concrete) on small radius sections.

I did get the chance to check the Lewisham extension on Friday (for the uninitiated, that's the bit between just north of Mudchute Station to Lewisham Station) but didn't notice any restrictions there.

 

[DanNCL]

Wonder if the sharp curve between Poplar and All Saints is one of the places that’s been slowed down? That always felt very quick.

I remember how amazed I was by some 1 (yes - one) minute DLR turnrounds at Lewisham in the past. If they still happen I can see how easily a small speed restriction could have an impact.

The turn back at Bank is impressively quick too. Because there’s no passengers in the turn back and because there’s no driver to switch ends, they can leave the turn back for the departure platform almost as soon as they’ve stopped.

For the Bank-Lewisham route especially, any slight speed restriction would have an impact. Probably not as much of an issue for Tower Gateway - Beckton where turnarounds are comparatively leisurely!

 

[vinnym70]

The whole section between Poplar and All Saints seems to be slower, curve and straights.
The section between Pudding Mill Lane and Bow Church seems to be slower although that may be a factor of that section being mostly single tracked.

 

[Sad Sprinter]

So this is a case of a system being not mediocre enough so it has to naturally be nerfed? Or that the trains were overspending? Which, having had a long DLR trip today, is a freighting thought giving the angles of some track curvature!

 

[vinnym70]

Not sure about overspeeding, the DLR has always felt reasonably conservative on speeds and given there's a lot of tight curves on raised sections, that feels very reasonable (and I'm sure is informed somewhat by the over-run at Island Gardens before the service started)

Will be interesting to see if we ever find out what the trigger is/was. Maybe testing of the new stock has highlighted something?

 

[Irascible]

An attempt to reduce maintenance costs?

 

[vinnym70]

An attempt to reduce maintenance costs?

Surely not now? The DLR has existed mostly as-is for so long now that it seems an unlikely out. Surely something has cropped up that literally everyone is surprised and but can't fail to act on?

 

[DGP]

I've posted this link from a London Standard article in the other DLR thread but I'm mentioning it here because it does refer to these speed restrictions.

 

[DerekC]

I suspect it's more likely that larger safety margins have been recently put in place meaning that the previous speed profiles no longer comply?

The Seltrac signalling/train movement control system was installed in 1992-96, initially on the Beckton Extension and then the rest of the system cut over to it. It was before the days of formalised safety case - it just depended on the HMRI (Kit Holden, a great guy) being satisfied that the system was safe. That took quite a long time and a lot of questions were asked during the design and installation process. I recall there being a discussion on the necessary margin between civil speed (the speed that the civil/mechanical engineers stipulate the train mustn't exceed given the curvature, superelevation and height of the centre of gravity of the train, basically), what should be set as maximum speed in the automatic train protection part of the control system, and what the ATO should drive to. (The previous system had ATO as well but I think the safety calculations were redone). As I recall, it was agreed that the margins could be tighter than on a manually driven railway given that the probability of an overspeed would be lower. I have no idea what's changed, but I think that @Peter Mugridge is probably right - somebody has done a check to a new standard. The other possibility is that the track maintenance regime is not that brilliant and that has given the safety guys the wobbles. Incidentally, changing speed limits is very easy on DLR - no signs or anything trackside involved, so changing back again would be easy too.

 

[Bikeman78]

The Seltrac signalling/train movement control system was installed in 1992-96, initially on the Beckton Extension and then the rest of the system cut over to it. It was before the days of formalised safety case - it just depended on the HMRI (Kit Holden, a great guy) being satisfied that the system was safe. That took quite a long time and a lot of questions were asked during the design and installation process. I recall there being a discussion on the necessary margin between civil speed (the speed that the civil/mechanical engineers stipulate the train mustn't exceed given the curvature, superelevation and height of the centre of gravity of the train, basically), what should be set as maximum speed in the automatic train protection part of the control system, and what the ATO should drive to. (The previous system had ATO as well but I think the safety calculations were redone). As I recall, it was agreed that the margins could be tighter than on a manually driven railway given that the probability of an overspeed would be lower. I have no idea what's changed, but I think that @Peter Mugridge is probably right - somebody has done a check to a new standard. The other possibility is that the track maintenance regime is not that brilliant and that has given the safety guys the wobbles. Incidentally, changing speed limits is very easy on DLR - no signs or anything trackside involved, so changing back again would be easy too.

One assumes that there is still a margin between the must not exceed speed and disaster? Automatic systems seems to err slightly on the side of caution, e.g. the 1967 stock on the Victoria line occasionally stopped short but I never had one overshoot.

Earlier this year I went on a tram in Gent in Belgium. It flew along the straight section along Princess Clementinalaan and barely slowed for the 90 degree bend before going under the railway. Quite alarming, but I guess the driver had driven around there enough times before to know what he could get away with. There don't appear to be any official speed limits at curves or junctions there.

 

[DGP]

There's been a Freedom of Information request to TfL about this and this is their response