4 car train

[Deleted]

Has anyone actually seen the 4 car train in operation? I remember it being mentioned in the Central Line timetable improvement in January 2020?

[superteacher]

Pretty sure none have run in passenger service.

[capitalomnibus]

Only 4 car version run on on the Waterloo & City line

[hobbayne]

I believe that they abandoned that idea after trials. Apparently, it kept getting gapped.

[noddymac]

The 4 car idea was indeed scrapped and deemed unsuccessful, so the shuttle is running as a full 8 car train.

[A Challenge]

Wasn't the whole point of the short set use that it meant they had two half sets not in use, and if that is not the case any more, how is the work being done?

[superteacher]

Oct 11, 2021 16:50:55 GMT A Challenge said:

Wasn't the whole point of the short set use that it meant they had two half sets not in use, and if that is not the case any more, how is the work being done?

Correct!

[jimbo]

I've yet to see how the planned shuttle service saves anything. Two trains to provide 3tph service including reversing times seems to me very inefficient. It requires two drivers and four operative cabs. The previous through trains avoided reversing time at Hainault platform, and instead took it at Woodford siding. By running through they had 20 minutes extra run time, which was covered by one 8-car train, one driver and two operative cabs.

[capitalomnibus]

Oct 10, 2021 20:40:55 GMT hobbayne said:

I believe that they abandoned that idea after trials. Apparently, it kept getting gapped.

What do you mean by getting gapped?

[superteacher]

Oct 11, 2021 21:19:34 GMT capitalomnibus said:

Oct 10, 2021 20:40:55 GMT hobbayne said:

I believe that they abandoned that idea after trials. Apparently, it kept getting gapped.

What do you mean by getting gapped?

Where all of shoes which pick up traction current are over a section gap, meaning that the train cannot draw proper, and thus cannot move.

[Chris L]

Oct 11, 2021 19:13:53 GMT jimbo said:

I've yet to see how the planned shuttle service saves anything. Two trains to provide 3tph service including reversing times seems to me very inefficient. It requires two drivers and four operative cabs. The previous through trains avoided reversing time at Hainault platform, and instead took it at Woodford siding. By running through they had 20 minutes extra run time, which was covered by one 8-car train, one driver and two operative cabs.

If the shuttle requires 2 trains for the Woodford-Hainault service four car operation on these would have meant 8 cars (or 1 train) is available for upgrading.

Unfortunately the infrastructure no longer allows 4 car trains to work the shuttle.

[rincew1nd]

Oct 11, 2021 21:19:34 GMT capitalomnibus said:

Oct 10, 2021 20:40:55 GMT hobbayne said:

I believe that they abandoned that idea after trials. Apparently, it kept getting gapped.

What do you mean by getting gapped?

The conductor rails supplying power to the trains have occasional gaps for a variety of reasons, sometimes for pointwork, sometimes to create two electrically separate sections of line. Because there are only a finite number of pickup shoes on the trains it is possible for all of the shoes to be above gaps in the conductor rail, with a four car train the likelihood of this increases (because there are fewer collector shoes).

If a train is moving slowly (eg over pointwork) and loses all pickups and doesn't have enough momentum to carry it along it is said to be "gapped". The solution is to deploy "gap jumpers" which are cables that supply power from the conductor rails to the train directly. Thry can be seen deployed in a manufacturer's photo here:

www.lcswitchgear.co.uk/product/gap-jumper-lead/

[capitalomnibus]

Oct 12, 2021 9:40:31 GMT rincew1nd said:

Oct 11, 2021 21:19:34 GMT capitalomnibus said:

What do you mean by getting gapped?

The conductor rails supplying power to the trains have occasional gaps for a variety of reasons, sometimes for pointwork, sometimes to create two electrically separate sections of line. Because there are only a finite number of pickup shoes on the trains it is possible for all of the shoes to be above gaps in the conductor rail, with a four car train the likelihood of this increases (because there are fewer collector shoes).

If a train is moving slowly (eg over pointwork) and loses all pickups and doesn't have enough momentum to carry it along it is said to be "gapped". The solution is to deploy "gap jumpers" which are cables that supply power from the conductor rails to the train directly. Thry can be seen deployed in a manufacturer's photo here:

www.lcswitchgear.co.uk/product/gap-jumper-lead/

So would the solution be to fit more pickup shoes? I guess this would not happen in this current climate with TfL finances

[Chris M]

I'm no expert, but I'd expect adding more pickup shoes to a train to be a very expensive and possibly time-consuming job, and one you'd have to do to at least most of the fleet so I'd be very surprised if there was anything close to a positive benefit-cost ratio for it even if TfL had the money to spend.

The other alternative would of course be to add extra sections of conductor rail in a few places, which while possibly costing more than modifications to a single unit would only have to be done once so may come out cheaper overall and has the potential to benefit future stock, but there is still no guarantee of a business case. I don't know whether it is even possible - gaps are there for a reason after all.

[norbitonflyer]

Oct 13, 2021 11:29:11 GMT Chris M said:

I'm no expert, but I'd expect adding more pickup shoes to a train to be a very expensive and possibly time-consuming job,

That would only be effective if the existing shoes were not all in the same gap. Adding more shoes in between the ends would not help if the gap was longer than the train.

(The problem of gapping was the reason for the "booster" design on the Class 70 and 71 electric locos on the Southern, as the locos were shorter than some of the gaps - for example at level crossings - which had been laid out with a two-car unit's length as the minimum distance between shoegears. The booster was essentially a motor-generator set with a big flywheel to keep it turning if power was lost.

I recall the Gatwick Express service ran into difficulties in its early days because of fires caused when a loco bridged a gap in which voltages were significantly different in the two conductors. Two shoegears close together on one vehicle left not enough cabling to handle the voltage drop, and power surges as supply was lost and regained too quickly for the control gear to handle, resulting in flashovers resulted.
sremg.org.uk/electric/class73.shtml

[spsmiler]

I'm just surprised that the conductor rail layouts were changed from the days when shorter trains were operated. There was a time when many lines ran short trains.

[noddymac]

Oct 13, 2021 22:46:53 GMT spsmiler said:

I'm just surprised that the conductor rail layouts were changed from the days when shorter trains were operated. There was a time when many lines ran short trains.

That’s why they were changed. Capacity increased, therefore the demand for shorter trains was no more, so all lines eventually saw 7/8 car lengths (excluding Waterloo & City).

With the Hainault/Woodford shuttle, it would have been great if a 4 car train worked, but sadly that’s not the case and I can’t see TfL spending more money to have the juice rails changed again to accommodate 4 car trains.

We’ll see what happens when the line eventually gets new rolling stock. I’m sure it’ll still remain at 8 cars, which is a waste.

[aslefshrugged]

The 4-car shuttles were only a temporary measure during the HOPL project, once that is completed they'll resume Woodford via Hainault services through central London so gapping won't be an issue

[35b]

Oct 14, 2021 1:22:32 GMT noddymac said:

Oct 13, 2021 22:46:53 GMT spsmiler said:

I'm just surprised that the conductor rail layouts were changed from the days when shorter trains were operated. There was a time when many lines ran short trains.

That’s why they were changed. Capacity increased, therefore the demand for shorter trains was no more, so all lines eventually saw 7/8 car lengths (excluding Waterloo & City).

With the Hainault/Woodford shuttle, it would have been great if a 4 car train worked, but sadly that’s not the case and I can’t see TfL spending more money to have the juice rails changed again to accommodate 4 car trains.

We’ll see what happens when the line eventually gets new rolling stock. I’m sure it’ll still remain at 8 cars, which is a waste.

I’m not sure I’d see the use of 8 car sets on Hainault-Woodford as a particular waste - if the Central line runs on 8 car sets, why run short sets as an exception with the extra constraints that imposes?

[Dstock7080]

Oct 14, 2021 7:07:38 GMT 35b said:

I’m not sure I’d see the use of 8 car sets on Hainault-Woodford as a particular waste - if the Central line runs on 8 car sets, why run short sets as an exception with the extra constraints that imposes?

Operating two 4-car trains on the shuttle would have released an 8-car train for the aforementioned CLIP refurbishments.

[brigham]

Oct 13, 2021 22:46:53 GMT spsmiler said:

I'm just surprised that the conductor rail layouts were changed from the days when shorter trains were operated. There was a time when many lines ran short trains.

I'm not remotely surprised at that.

Anything which adds flexibility is usually 'rationalised-out' at the first opportunity.

[35b]

Oct 14, 2021 7:23:19 GMT Dstock7080 said:

Oct 14, 2021 7:07:38 GMT 35b said:

I’m not sure I’d see the use of 8 car sets on Hainault-Woodford as a particular waste - if the Central line runs on 8 car sets, why run short sets as an exception with the extra constraints that imposes?

Operating two 4-car trains on the shuttle releases an 8-car train for the aforementioned CLIP refurbishments.

Short term, yes. My point was about the long term.

[alpinejohn]

Are people overstating the 4 car gapping problem - and in effect slowing down the CLIP upgrade project?

I assume it is not impossible for a few of the more experienced drivers on this route to quickly produce a map showing the locations where a short 4 car train may end up gapped - ie places to avoid stopping. OK they may have to do a few test runs to identify all the risks, but surely it must be possible to spot a long chunk of track with no power rails...

Then I suspect it would also be able to identify any problematic signals likely to result in a train stopping in those gaps.

Armed with that information a quick fix would be to erect some sort of warning boards ahead of those locations - IE min speed past this point of x mph to ensure a train has enough momentum to clear the gap.

Given this extra information (sort of additional route knowledge) most competent drivers should have no problem operating a 4 car set on route - save the need for any incident requiring an emergency brake application(child playing on track).

Yes there is the extra hassle for depot staff to first split the chosen train and check the 4 driving positions are serviceable. Eventually depot staff can presumably reform the train into 8 car format very quickly, once all the trains have been through the CLIP upgrade - assuming someone can actually make a credible case for doing so.

However I rather doubt there is any time of day where a 4 car train cannot comfortably handle typical passenger numbers on the Hainault-Woodford shuttle. Operating a 4 car train should reduce power consumption and reduce wear and tear on rolling stock.

[jimbo]

Central line trains do not normally have driving cabs, except at each end. So two four-car trains are not simply made by splitting a full train, as was the case with their predecessors! With the previous through service there was only one extra eight-car train required due to no lay-over at Hainault. So replacing that with two four-car shuttle trains did not release a spare train!

[norbitonflyer]

Oct 14, 2021 8:23:09 GMT alpinejohn said:

.....but surely it must be possible to spot a long chunk of track with no power rails...

........erect some sort of warning boards ahead of those locations - IE min speed past this point of x mph to ensure a train has enough momentum to clear the gap.

You are unlikely to find long gaps in the live rails on long stretches of plain track. Most gaps are at complex pointwork, where the current rails of one track have to be interrupted by the running rails of the intersecting track. Dictating a minimum speed at such complex pointwork is probably unwise.

(This is less of a problem in 3rd Rail Land as there are two possible sites for the (one) current rail, one each side. On LU, there is only one place you can put the negative rail.)

[norbitonflyer]

Oct 14, 2021 8:52:22 GMT jimbo said:

Central line trains do not normally have driving cabs, except at each end. So two four-car trains are not simply made by splitting a full train, as was the case with their predecessors! With the previous through service there was only one extra eight-car train required due to no lay-over at Hainault. So replacing that with two four-car shuttle trains did not release a spare train!

Indeed, although there are more 2-car units with driving cabs than without (175 to 165) so that some trains are normally formed with a driving cab in the middle of the train, they do not usually put two middle cabs in the same train as that would reduce its capacity - and lead to extended dwell times as passengers find cab doors where they expect passenger doors.

If you do the arithmetic there are enough units to form 85 8-car trains, of which five would have an extra driving cab

[Tom]

Oct 14, 2021 8:23:09 GMT alpinejohn said:

I assume it is not impossible for a few of the more experienced drivers on this route to quickly produce a map showing the locations where a short 4 car train may end up gapped - ie places to avoid stopping. OK they may have to do a few test runs to identify all the risks, but surely it must be possible to spot a long chunk of track with no power rails...

Then I suspect it would also be able to identify any problematic signals likely to result in a train stopping in those gaps.

And that's exactly what's done in a gapping analysis study, it's just done using drawings of the conductor rail layout and the shoegear positions by people who know the assets involved, rather than by drivers who go over the gaps at speed.

Oct 13, 2021 22:46:53 GMT spsmiler said:

I'm just surprised that the conductor rail layouts were changed from the days when shorter trains were operated. There was a time when many lines ran short trains.

Bearing in mind that short trains ceased in the 1960s (except for the Met and District) and the requirements for gapping around point layouts and at substations changed later, based on a set of regulations which were introduced in 1989, it's not really that surprising.

[gantshill]

I presume that short trains on the Central and Piccadilly lines continued until the closure of the Aldwych and Ongar branches in 1994. If not on the whole line, at least as far as the relevant depots and sidings.

[metman]

Yes the branches involved ran short trains until closure. The Central Line short trains only ran around the top of the Hainault loop and to and from Ongar. The 1973 stock train on the Aldwych service ran out of service once it left the branch.

Otherwise full length trains ran on the rest of the lines after uncoupling was ended in about 1959.

Only the Metropolitan ran short trains until 2011 on the Chesham shuttle and some transfer trips to/from Rickmansworth/Neasden, some in and not in service.

Anyway we are slipping off topic…..

[d7666]

Oct 14, 2021 8:23:09 GMT alpinejohn said:

Are people overstating the 4 car gapping problem - and in effect slowing down the CLIP upgrade project?

I assume it is not impossible for a few of the more experienced drivers on this route to quickly produce a map showing the locations where a short 4 car train may end up gapped - ie places to avoid stopping. OK they may have to do a few test runs to identify all the risks, but surely it must be possible to spot a long chunk of track with no power rails...

Then I suspect it would also be able to identify any problematic signals likely to result in a train stopping in those gaps.

Armed with that information a quick fix would be to erect some sort of warning boards ahead of those locations - IE min speed past this point of x mph to ensure a train has enough momentum to clear the gap.

Given this extra information (sort of additional route knowledge) most competent drivers should have no problem operating a 4 car set on route - save the need for any incident requiring an emergency brake application(child playing on track).

Yes there is the extra hassle for depot staff to first split the chosen train and check the 4 driving positions are serviceable. Eventually depot staff can presumably reform the train into 8 car format very quickly, once all the trains have been through the CLIP upgrade - assuming someone can actually make a credible case for doing so.

However I rather doubt there is any time of day where a 4 car train cannot comfortably handle typical passenger numbers on the Hainault-Woodford shuttle. Operating a 4 car train should reduce power consumption and reduce wear and tear on rolling stock.

It is a lot more complex that that. It is an ATO railway. Your driver responding to a lineside warning board is not how the Central Line works. To ensure enough momentum through a gap requires trackside signalling changes to ensure the "go-codes" enable the correct level of motoring AND at the same time maintain train protection; the on train run data firmware will need updating too. Coded manual driving won't fix this either, CM gets the same go-codes as ATO.

<<Rincew1nd: emphasis in quote changed from red to bold>>