4 car train

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

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

Correct!

What do you mean by getting gapped?

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.

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

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

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?

I'm not remotely surprised at that.

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

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.

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.)

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.


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.

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…..