75Modern Railways JULY 2011 www.modernrailways.co.uk

This summer, the London tube passengershould see better train services – on twolines at least. Two stages in the long and

painful slog to bring the ageing system up tomodern standards are close to completion. Oneis on the Victoria Line with the replacement ofthe last of its 1967 tube stock trains and its old-style automatic operation. The other is on theJubilee, with the completion of its conversion toAutomatic Train Control (ATC).

Both projects started back in 2003, under thenow defunct Public Private Partnership (PPP)and today, despite the collapse of the whole PPPstructure and eight fraught years of design,planning and implementation, signs are obviouson the ground that new things are happening.

The Victoria LineOn the Victoria Line, the original trains, theiconic 1967 stock, have been replaced by new2009 stock sets built in Derby by Bombardier.This month sees the last of the old trainsremoved from service so that the line can adoptthe regenerative capabilities of the new trainsand start reducing the heat dumped into thetunnels during braking – good publicity for the

summer. While the effect for individualpassengers will hardly be noticed, at least a startwill have been made in containing the rise intemperatures underground.

The removal of the old trains will also allowthe full implementation of a new ATC system,the Invensys (formerly Westinghouse) DistanceTo Go – Radio (DTG-R) product. Theequipment has been installed in overlay modeon top of the original Westinghouse ATC and thenew trains are using it but, as long as the oldtrains were in use, the original ATC trainseparation had to be retained. Now a start hasbeen made on stripping out the original systemand introducing the upgraded DTG-R capabilityto reduce the train separation distances. The firstchangeover took place between WalthamstowCentral and Tottenham Hale on 31 May and theremainder of the line will follow in stages overthe next year.

The JubileeIn parallel with the Victoria Line, the JubileeLine has been going through its own publicallytraumatic conversion to ATC, with several yearsof frequent weekend closures for installation and

testing and a couple of lengthy in-servicefailures during the subsequent shakedownperiod. So far restricted to the line south ofDollis Hill, the new system was due to be fullyoperational all the way to the northern terminusat Stanmore from 27 June. The Jubilee uses theThales (formerly Alcatel) SelTrac S40 system,similar to that on the Docklands Light Railway,but it is substantially different from the VictoriaLine’s DTG-R.

For a start, DTG-R retains track circuit traindetection. Track circuit occupancy andinterlocking status information is sent to eachtrain, using radio transmission, to form the basisof its DTG calculations with its on-board routemap, so that the train knows its permitted speedand the distance to its limit of movementauthority. This allows it to approach thepreceding train more closely than was possibleunder the fixed overlap system used by theoriginal ATC system.

S40 doesn’t have on-board maps, radio ortrack circuits. The transmission system usestrack-mounted loops, crossed every 25m toprovide fixed location markers. A ‘vehicle on-board computer’ (VOBC) is used to determine

London Undergroundgets more automatedPiers Connor reviews LU’s resignalling policy

1996 tube stock arriving at Stratford in CBTC mode withconventional signals ‘bagged’ on the left. Kim Rennie

76 www.modernrailways.co.uk JULY 2011 Modern Railways

train location. Each train calculates its progressalong the line and continuously transmits this tothe Vehicle Control Computer (VCC) for thearea. The VCC can control up to 40 trains at atime, although the LU installations will not needmore than 20 under normal conditions. TheJubilee Line has five VCCs and the NorthernLine, which is now being equipped with thesame system, will get six.

A feature of the UK version of the S40 systemis the use of axle counters as a secondary means

of train detection or for ‘non-equipped’ trains.Docklands had them imposed on them, so it wasa foregone conclusion that LU would have tohave them too. They are also used to confirmroute occupation for point locking.

PPP collapseBack in 1968 when London Underground (LU)opened the initial section of the Victoria Line, itwas the first metro in the world to build a newline fully equipped with ATC. This year, LU goesfor the triple crown – the first metro in the worldto adopt three different ATC systems on threedifferent lines, two of which share part of thesame route and one of which shares it with trainsthat will not be equipped with ATC.

Now the conversion to ATC of an existing,high capacity, urban railway, running trains everytwo to three minutes, isn’t for the faint-hearted,especially if your political masters have tied oneof your hands behind your back by imposingserious interface problems on you from the start.

On the Jubilee Line, which shares 4½ miles ofits route between Finchley Road and WembleyPark with the Metropolitan Line, the PPPorganisation drove a wedge between theinfrastructure owners of the two lines. LondonUnderground watched, seemingly helpless, as thetwo infrastructure contractors, Metronet for theMetropolitan Line and Tube Lines for theJubilee, chose different train control systems –Westinghouse DTG-R for the Metropolitan andother sub-surface lines (SSL) and S40 for theJubilee. Giving a paper to the Institution ofRailway Signalling Engineers some years later,one project engineer described it, rather tactfully,as ‘unfortunate’. He was being generous. It wasridiculous.

Further weaknesses of the PPP structure led tothe collapse of Metronet in 2007 and LUmanagers quickly dumped the WestinghouseSSL contract as too expensive. Bearing in mindthat the price per km was 35% more thanSelTrac’s, who could blame them? However, Idoubt the two-year overrun on the Jubilee Line

implementation and all the technical problemsthe installation and testing has brought on willhave allowed Thales to keep to its original costbase.

Tube Lines absorbedThen, in June 2010, Tube Lines was purchasedby Transport for London (TfL) and the PPP wasfinally dead. It was hailed as a wonderfulopportunity to overcome the signalling interfaceissues and get a sensible, railway-orientatedapproach to resignalling the jointly operated partsof the system. The purchase was greeted byKulveer Ranger, Mayor Boris Johnson’stransport adviser at the time, as ending theridiculous situation on the Metropolitan/Jubileeroute. ‘So now we have that bit of track, we canactually procure a contract that meets thatrequirement,’ he said. ‘It means the contractorcan actually deliver what’s required, rather thantwo contractors having two different systems onthe same part of track.’ Oh really?

Just over a year later, in June 2011, acompletely new and untried contractor wasconfirmed as the supplier for the SSLresignalling and Mr Ranger was shunted intoTfL’s ‘Environment and Digital London’departmental siding. The new contractor isBombardier and the new system is thatcompany’s ‘Cityflo 650’ product. This will coverthe Metropolitan, Circle and District Lines and,the word is, the contract contains an option toresignal the Piccadilly Line. If this happens, itwill take the interface risk out of two moredifficult areas – the Rayners Lane to Uxbridgesection shared with the Metropolitan and thejoint District/Piccadilly section between BaronsCourt and Hanger Lane Junction, near NorthEaling.

Most strangely, when it announced the choiceof Bombardier, TfL said of the originalWestinghouse offer, ‘It would also have left LUwith the legacy of a signalling system notcompatible with others across the tube network’.No, I couldn’t see what they meant either.

Acronyms

■ ATC: Originally the Great WesternRailway’s ‘Automatic Train Control’system, which was the forerunner ofAutomatic Warning System (AWS). Now,ATC is a catch-all term for an integratedATS, ATP and ATO system. In the UK, wesometimes use ATO to mean ATC.

■ ATP: Automatic Train Protection – thebasic safety system that prevents over-speeding and train collisions withouthaving to rely on the driver to do it.

■ ATO: Automatic Train Operation – doesthe driving and braking without driverparticipation. Sits on top of ATP.

■ ATS: Automatic Train Supervision – asystem which can, if properly designed,help controllers and signallers make theright choices in train service management.Usually works better if the controllers andsignallers don’t fiddle with it. Sits on top ofATP and ATO.

■ CBTC: Communications Based TrainControl – generally agreed as a system thatdoesn’t use track circuit coding to controlthe trains. Rather, it uses separatetransmission cables or aerials and inductionor radio.

■ TBTC: Transmission Based Train Control –the same as CBTC. It just depends onwho’s describing it.

Radio So why did LU, with every opportunity to adopta mature, accepted and now proven, signallingsystem across the jointly-operated parts of theirnetwork, choose yet another supplier and digitself a huge new interface hole that’s going tobe even bigger than the one it is still deeplyinto? Cityflo 650 isn’t proven in the UK and ithas to go through the trauma of getting acceptedby LU, whose safety elfs would scare the paintoff the hardiest garden gnome, as well asNetwork Rail’s equally Tolkienesqueacceptance processes to let it work over theRichmond and Wimbledon branches. And it hasto slot into S40 on the Jubilee Line, theMetropolitan’s existing system, the newsignalling currently being installed in Neasdendepot (yes, of course it’s different from all theothers, need you ask?) and whatever NetworkRail has on its bits of track used byUnderground trains.

Well, the clue to our question is in a commentby a senior LU engineer who remarked to me,‘I don’t want any more of that b****y cablelying around on my railway’. Apparently, theS40 transmission system isn’t too popular withcertain sections of the Underground hierarchy.The major difference between Cityflo and S40is that the train to wayside transmission systemfor Cityflo is radio. The dreaded track-mountedcables are not needed. I haven’t been able to getanyone to tell me why the cable system waschosen with SelTrac when Thales already had aradio transmission system available but Isuspect it was regarded as ‘not sufficientlyproven’ back in 2003.Spanish seductionIt seems as if the Cityflo choice has come as aresult of a careful seduction campaign byBombardier, which has used its Spanishconnections with the Madrid metro, where it hasrecently installed its Cityflo 650 system withoutthe long weekend closures that we’ve had to getused to in London. The hope, apparently, is toride on the back of track and station upgrade

closures so that no one will notice the newsignalling going in.

How this will work while on-line testing of thesystem – the really difficult part of the business –is being done, is anyone’s guess. The architectureof the Cityflo system is very similar to theJubilee’s S40’s and one of the reasons for thelong drawn-out testing regime was the need totake over long sections of the Jubilee so that theVCCs could be validated. For the Cityflo system,the control areas are known as ‘Regions’.

Bombardier has a huge task ahead of it. Itssignal engineers will not be familiar with thecomplex LU engineering philosophy and its rigidoperating procedures and LU doesn’t know the‘Ebilock’ interlocking technology (remember theaborted Horsham installation?) nor the traincontrol system. The latter has its origins in theAmerican Westinghouse airport people-moversystem, like the one at Gatwick Airport, wherelittle, four-wheeled shuttle cars trundle up anddown between terminals. Transferring thattechnology onto complex junctions like Earl’sCourt or Harrow-on-the-Hill will be just as‘challenging’ as the S40 has been.

That said, LU now has hard-won experienceof upgrading two lines and there are lessons to belearned from Madrid, so hopes are that theCityflo conversion will be rather less traumaticthan the Jubilee Line changeover. The spin fromBombardier was that there was a high level ofco-operation between operator and supplier inMadrid and that there was a carefully-stagedoverlay programme. Like London’s Victoria Lineproject, old and new systems operated togetherthroughout the upgrade. We can only wait andwatch.

Vic vs Jub?There is a perception that the Victoria Lineupgrade has gone better then the Jubilee’s. Thismay not be entirely fair. Time-wise, they havealmost run in parallel, with the Jubilee actuallyahead for completion this year. Both have hadrolling stock changes – the Victoria getting all

new trains and the Jubilee increasing its stocklength from six-car to seven-car sets – and bothhave had weekend closures. The Victoria Linealso used early evening closures to provide moreinstallation time at night.

Perhaps the real difference has been that theVictoria Line is a self-contained railway with fewsignalling interfaces, whereas the Jubilee has acomplex set of interfaces with the Metropolitan,particularly at Neasden and Wembley Park. Forsome possessions, it was necessary to close theMet as well as the Jubilee.

The differences between the two systems hada part to play. The distributed architecture of theVictoria Line’s DTG-R system allowed stagedimplementation and single trains could be testedwhile old trains were still running. Training wasalso staged as the new trains went into servicemixed with old trains. The old and new ATCsystems could operate in passenger servicetogether.

The Jubilee couldn’t do this, as all trains andstaff had to be in place for the new system to golive. There were also considerable technicaldifficulties interfacing the S40 systems with theoriginal Westinghouse equipment, whereas bothVictoria Line systems were Westinghouse-based.

Back-upA big question for the discerning ATC buyer iswhether or not to have a backup system. Goodquestion, since some systems do and some don’t.Even within LU, the Jubilee Line’s S40 does butthe Victoria Line’s DTG-R system doesn’t. Youmight ask why this is, since all ATC systemsincorporate ATP and trains will stop if somethinggoes wrong.

After all, the traditional, fixed block, colour-light system we all know and love doesn’t havea back-up system, apart from the rule book, andneither does TPWS. Why should metro ATCsystems be different?

The answer lies in our love affair with thetrack circuit. Most operators just can’t wrenchthemselves away from the traditional form of

77Modern Railways JULY 2011 www.modernrailways.co.uk

Far left: Under the SelTrac S40 CBTC system on theJubilee Line, a Stanmore train is standing just 90min rear of another stationary train in the platform atWillesden Green. Under the old, fixed block system,at this location, the separation between the twotrains would have been 376m. A Metropolitan Line(right) train passes on the next track, operatingunder the old fixed block system. Richard Griffin

Left: The Victoria Line was resignalled north ofSeven Sisters over the 28-30 May bank holidayweekend for Distance To Go signalling. As a result,1967 tube stock was no longer able to workbetween Seven Sisters and Walthamstow Central.A northbound 1967 tube stock service calls atKing’s Cross St Pancras on the evening of Friday 27May 2011, the last day such trains could run toWalthamstow Central. Kim Rennie

Right: Jubilee Line CBTC signalling ‘Ready toDepart’ platform indicator. These are provided nowthat conventional station starting signals andplatform repeaters have been removed. Kim Rennie

train detection provided by the track circuit.Anything else seems too reliant on shakytransmission systems like radio or inductionloops. If you lose the communications, they say,how do you know where your trains are and,more importantly, once you’ve lost them, howcan you find them again?

Both S40 and Cityflo use fully redundantcomputer systems to run large areas of theirtransmission-based train detection systems but,if an area control falls over, up to 20 trains canbe wiped off the computerised memory map. Ofcourse, the system is designed to stop all the losttrains immediately but, to recover, it then has topoll each train to find out where it is and whichway it is facing and then calculate therelationships with other trains before it canrestart the system. This effectively shuts downthe whole line.

In a recent incident on the Jubilee Line, aVCC glitch required it to be ‘rebooted’ to clearits memory of a virtual train. This meantclearing the area under its control of real trainstoo. This took half an hour. After rebooting, atest train had to be sent through the area to testthe system and reset the axle counters used inthe back-up system. This took another hour.

Cityflo attempts to get over this with its ‘TrainRegistry System’, which independently trackstrain movements and can then be used to updatethe ‘Regions’ if one falls over.

Having a back-up system may make theoperator feel comfortable at the contract signingstage but there is little evidence that, in the heatof battle, it provides anything more than a slowspeed train detection system that is no betterthan the restricted manual speed of 10mphprovided by the ATP. Not only that but, if theback-up system fails, it rebounds on the mainsystem, causing restricted movement throughthe area. In the end, it costs more to provide, itcosts more to maintain, it adds another failurerisk and it offers no tangible improvement inservice recovery. So, why have it at all?

BenefitsThe Underground’s upgrades are alreadyshowing benefits, with the new trains on theVictoria Line providing a reduction in dwelltimes. Their faster operating systems allow dooropening and closing times to be reduced and thelag between doors proved closed and wheel startto be shortened.

More benefits will come. Now all the oldtrains have gone, the long overlaps can beremoved and the old interlockings disconnected.Within a year, the new track circuits andWestrace interlockings will have total controland it will be possible to reduce headways.

A big benefit of ATC is in train serviceconsistency and recovery. Just eliminating‘defensive driving’ and variable brakingtechniques on a manually-operated route willgive an extra 2.5 trains per hour (tph). If you canshorten the distances between trains too, usingATP systems like DTG-R or S40, you can getanother train or two per hour.

On the S40 system, a train can stop as close as80m behind the one in front, somethingimpossible with the old, trainstop-based system.

This ability provides for rapid recovery fromminor delays and, combined with the ATS,allows a better balance of trains along the route.

On the Jubilee Line, with the new ATC inplace, the ATS adjusts the speed of trains to evenout the service or lets trains recover time. Theanomalies of manual driving are eliminated andtrain speeds are adjusted to the circumstancesdetected by the central computers. Already this isvery apparent, as some trains appear to movequite gently along the line, while others performup to their full limits. It just depends on the statusof the route at the time. The same sort of serviceadjustment can be applied to the Victoria Line.

Under good conditions, the manually-operated Underground routes can manage 24-28trains per hour (tph) depending on the existingsignalling and the terminal arrangements. If allgoes according to plan, the Jubilee Line will geta new timetable in July that will offer a step upfrom 24 to 27tph. Once the system has fullybedded in, it will be possible to increase this. On

the Victoria Line, once the asset replacementprogramme is completed in a year’s time,another 2-3tph can be added to the timetable.

Naturally, this pragmatic approach toperformance improvement has been spun outof control by the TfL press office which says,‘the overall SSL upgrade programme willincrease capacity on the District Line by 24%to 50,000 passengers/hr, on the MetropolitanLine by 27% to 44,500 passengers/hr and onthe Circle and Hammersmith & City Lines by65% to 43,500 passengers/hr’.

Since the official maximum capacity for abrand new seven-car ‘S’ stock train is 1,194,to get 50,000 passengers/hr on the District,you would need 42 trains per hour. I doubtBombardier has signed up for that. MR

Piers Connor is an independent railwayconsultant and lecturer on railway operationsand engineering. His website is at www.railway-technical.com

78 www.modernrailways.co.uk JULY 2011 Modern Railways

Dollis Hill on the Jubilee in thesouthbound direction, where CBTCtakes over from the old signalling.Original automatic station starting

signal A 171 is covered over and out ofuse. Below is new signal WIG 002 which

marks the ‘migration point’ betweenconventional and CBTC signalled areas.This displays either a red (stop) or blue

(proceed in TBTC) aspect. Kim Rennie