Rat Race

The RAT (Rail Adhesion Train) was running on the east end of the Central line today. As I was waiting at WOO (Woodford) for a train that would take me on to LIS (Liverpool Street) I was pleasantly surprised to see a RAT pulling into Eastbound platform 3 as the WOO train pulled into the siding (its name is 21 road). A RAT, for those of you who don't know, does pretty much what it says on the tin and it's a bit like a gritting lorry for the railway. RATs drop sand (or a mixture of sand and something else, I'm not exactly sure what the Underground use, but I think it's almost certainly Sandite?) onto the running rails (the rails which the wheels run along, as opposed to the "conductor rails", or "juice rails", which carry the traction current). This helps provide grip for the wheels. As I understand it, RATs are used to deal with the oft-derided problem of leaves on the line. Before the sand(ite) is dropped, leaves are cleared from the rails using jets of water. The sandite is then sprayed onto the rails to provide traction, as the sandite increases friction between the wheels and the rails. On London Underground, they're only really used, I believe, on the Metropolitan and Central lines, as these lines travel through the more heavily wooded areas and so face potential problems with leaves on the line.

RATs are of interest to train nerds, at least partly, because they're fairly uncommon. Also, on the Underground, they're built from converted former passenger trains, which gives us nerds a chance to look at old tube stock. On the Central line, the old 1962 stock trains were converted into the RAT. The 1962 stock:

A 1962 stock train, which is, I believe, operating as a RAT in this picture. These days, though, the RATs have a shiny new paint job in LUL red white and blue. (Image courtesy of "Sunil060902" (via Wikipedia))

Served the Central line from 1962-1995, when the last one was finally replaced by the new (well, new then, at least) 1992 stock, just visible in the picture above. Some of them were transferred to the Northern line, but only for a very brief while. The last 1962 stock train left passenger service in November 1999. Interestingly, the 1962 stock were built before the introduction of OPO (One Person Operation) and were designed to be operated with a guard - the guard having a control panel inside the passenger compartment. I believe that guards survived on the Central line until the last 1962 stock train was withdrawn, but I may be wrong. The sticker informing passengers that the relevant door is not to be used when the guard is using it is still visible on the RAT - even though no passengers - or guards - travel on board - the carriages are full of pipes and sandite.

Apart from that, there's not too much detail worth going into. I got on C-stock (the C is for "Circle", by the way) trains between LIS and Euston Sq. in both directions, but I noticed that the rollout of the S7s is moving along nicely and I didn't see many other C-stocks out and about.  Another DEB train and another long wait at WOO on the way home, though, I really must time that better tomorrow. One thing to mention, however, is that I saw a train in the sidings at Farringdon. Again, this isn't fantastically unusual, but it isn't fantastically common either. As far as I know, trains aren't timetabled to terminate at Farringdon during the day, those sidings are mainly used in the case of disruption, or to recover time from late running. I don't know why this particular unit was in the sidings, but I thought it was worth a mention. Farringdon used to have three sidings which, as I say, even recently saw quasi-regular use if a train needed to be "short-turned" (reversed at a station before it's original destination) for whatever reason. A short while ago, however, one of them was taken out of service (25 road I think it's called?), and half of the track has gone. The sidings at Farringdon are not long enough to accommodate the new S stock trains (neither S7 nor S8) so they're going to be redundant pretty soon. There's been a bit of talk recently about what to do with them. I've heard that crossrail, or some of the national rail services that pass through Farringdon mainline station, may make use of them (or, at least, of the space they currently occupy) but I don't think there are any definite answers yet. Farringdon also has a crossover at the King's Cross end of the station (the sidings being just outside Farringdon, between Barbican and Farringdon). A crossover is a vaguely S-shaped bit of track (actually it looks more like this: |\|) that connects two lines. The Farringdon crossover is clearly visible in this picture:

A picture of Farrindon station clearly showing the crossover. (Image courtesy of Dr Neil Clifton (via Wikipedia))

A crossover allows trains on the eastbound (EB) track to cross over onto the westbound (WB) track and/or the other way round. The train will pass over the crossover, from the EB track to the WB track (or vice versa) and stop when the whole train has cleared the crossover. This is a simple way of reversing a train. The precise sequence of events depends on the crossover and the direction, but let's take the example of this crossover at Farringdon. A train on the eastbound platform (the one on the right, from which our picture was taken) would normally have arrived from King's Cross, with the T/Op obviously at the front of the train. Therefore, when the train stops, s/he will be at the Barbican end. As you can see in the picture (we're looking towards King's X), this is the wrong end. Therefore, the T/Op will change ends and will detrain the passengers as well - if necessary. S/he will then be cleared over the crossover, onto the eastbound track. Now, the train could then continue to King's X (in this case, it's unlikely passengers would be detrained), or it can stop at a little sign with "Limit of Shunt" printed on it, which indicates that the back of the train has cleared the crossover. The T/Op will then change ends again, drive the train back into Farringdon (this time, into the westbound platform) and re-enter service. Obviously, it will be necessary to again change ends and then the train can continue to King's X. This is a bit of a fuss to be honest. Now, a train on the westbound platform (the one on the left) will be detrained first. It will then head out of the platform on the WB until it reaches the limit of shunt board, where it will stop. The T/Op will change ends and drive the train back over the crossover into the EB platform. Here it will re-enter service and continue on to Barbican.

As you can see, however, the crossover at Farringdon is actually within the platform and while this was practical for the much shorter C stock, the S stock train is much too long. A C stock train, like the one in the picture, actually comes to a stop in the EB (right hand) platform with the back of the train just past the crossover, so it can be used. The back of an S stock train in the eastbound platform, however, will be much further up the platform than that crossover, so it can't be used, at least not without a palaver involving the train moving forwards on the EB track until the whole train had passed the crossover, and then reversing over it. The crossover couldn't be used in the other direction for the same reason - the front of an S stock train using this crossover would be way outside the platform by the time the whole train had cleared it. The problem with this is that the train would have to continue to Barbican empty before it could re-enter service. In the scenario described above, when the train heads over the crossover into the eastbound platform, from the WB track, by the time the whole train has cleared the crossover, the front of the train will be on its way to Barbican. Thus, with the new trains, the crossover is pretty useless, too. I say that, but I think it is possible that it could be used, it just wouldn't be used very often, because it's such a hassle. This is a problem, as Farringdon is a useful reversing point in the centre of London if there's a problem. There is also Moorgate, King's Cross St. Pancras, Baker Street, Aldgate, Edgware Road (and Tower Hill for the Circle line) but all the same, the loss of reversing facilities at Farringdon will be a loss.

As another little tidbit, some of you may have noticed that a few weekends back a train actually derailed in the Farringdon sidings. It was a very minor incident and I don't really know what happened, but it looks like the train just came off the rails as it was pulling out of the sidings at low speed. Very minor incident, no passengers involved, although it did screw up the H&C and Circle lines a fair bit.

Happy travelling :)