When London Underground’s Victoria Line opened in 1968, it measured 21km long and was the first metro in the world to have Automatic Train Operation (ATO). This was a revolutionary step and the system was designed under the guidance of the legendary London Underground signal engineer, Robert Dell.
Using different frequency track circuits for the essential train commands, the system worked well for over 40 years but by the early 2000s the technology looked obsolete and more modern systems of ATO had emerged. The trains, too, were nearing the end of their life and so a complete renewal of the system was planned. Replacing one ATO system with another, whilst keeping the railway in operation, was itself a challenge. A suitable method of doing this was devised and the last old trains were finally retired in mid 2011.
So how was it done and what were the challenges along the way? the rail engineer recently visited the Northumberland Park control centre along with a group of IRSE members to find the answers.
As with any replacement system, making the old technology work with the new led to a number of choices. Should the old trains have the new system additionally installed so that when parts of the infrastructure were converted, the trains could operate to the new control commands? This was rejected as too complex and costly. Duplicating the ground based system was the alternative, but could this be done? The eventual solution was to acquire a train control system that could be overlaid on to the existing such that the SIL 4 interlocking and train protection information was conveyed to both the old and new trackside communication equipment in parallel.
The system chosen was supplied by Invensys Rail. At its heart are a number of Westrace microprocessor interlockings that generate the route setting and route holding requirements as well as generating the train movement authorities. Linked to the interlockings is a self-contained radio network, entirely based on radiating cable, which communicates the commands to the trains. The system is termed DTG-R – Distance to Go-Radio – and is fixed block, i.e. there are always fixed distances between succeeding trains, to which are transmitted the distance to go commands. Train detection is achieved through the new FS 2550 track circuits, a standard jointless product from Invensys which has replaced the old coded track circuits once all the old trains were withdrawn.
APR (Absolute Position Reference) balises are positioned periodically between the running rails to give accurate information to the system on the position of every new train, this being an integral part of the ATP (Automatic Train Protection) system. These balises are passive devices, obtaining their power by inductive coupling from an under- train APR reader. A different radio frequency is allocated to each block section, these being in the 170 and 180 MHz band. The new trains are equipped with two side and one roof aerials that receive the command signals in parallel. The ATP system is rated as SIL 4 whereas the ATO equipment is SIL 2. This has become the norm for automatic metro operation.
The radio system has been supplied by TE, a UK firm that has established itself in the track-to-train radio market. A base station is located at every signal equipment room with the command signals fed to both ends of the radiating cable via an optical fibre link to keep the system in operation should a cable break occur. This radio system is completely independent of the ‘Connect’ radio network that is in use across London Underground for voice communication to trains and station staff.
In the event of Automatic Train Control (ATC) failure, the system can be operated in Restricted Manual Mode at 15km/h under signals. If the train ATP has lost its location information, a minimum number of two APRs are required to be read, plus a confirmation of correct block occupancy, before ATC operation can be re-established. Should the ATO fail or ‘go lost’, the system has the ability to run in Protected Manual Mode allowing the driver to drive at full line speed as if the ATO did not exist. This feature minimises disruption.
Controlling the line
The Victoria Line control centre was originally at Cobourg Street near Euston. As it was impractical to build the new control arrangements there, brand new accommodation has been built at Northumberland Park, the site of the line’s train depot. Known as Osborne House, it commemorates Queen Victoria’s favourite holiday residence. Since the Victoria Line is an end to end railway, controlling the line is relatively simple. Some trains terminate short of the end destinations on a timetabled basis, but this can also happen when service or passenger disruption occurs.
The system currently allows 30 trains per hour (tph) but this will be increased to 33tph from January 2013. The control room is equipped with seven universal desks with multiple VDU workstations that are used by the line controllers. Also provided is a large overview panel so that everyone in the room can see at a glance the position of every train. This latter feature was contentious and had to be fought for by the staff.
Whilst the trains operate in ATO mode, the regulation is still done manually. If gaps appear in the service, then the controller intervenes to hold a train at a key station to even out the service. It is anticipated that ATR (Auto Train Regulation) will be introduced at some future time.
The controller responsible for communications has facilities to control the line’s CCTV, PA and tunnel telephone systems as well as monitoring other communications assets. Station facilities such as escalators are the responsibility of local station control rooms. All controllers have access to the LU Connect radio system enabling instant communication with drivers and station staff.
The control room system uses current technology to connect the information together. A central services processor is at the heart of a WAN (wide area network) linking the desks and diagrams within the room as well as connecting to a local site computer at each of the 16 stations. This system has multiple layers of redundancy and uses IP addressing. All this is non safety designated but is at the heart of the decision making for the regulation of the line.
As with all ATO railways, the operators have little to do while the line runs normally but, when disruption occurs, the actions of the controllers are key to restoring the line back to normality. This requires them to undertake regular training in a simulation room. From here, many conditions can be applied including failures and unusual events such as track circuit problems, train failures, timetable degradation, passenger alarms, even suicides which are known as a ‘one under’. Operators are tested as to how they handle these but the tests are scripted so as to be seen as fair to all.
The communications systems are also simulated, enabling the operators to practice how to communicate with station staff. Similarly, a cab simulator using an interactive white screen is used for driver training where different conditions (even snow – most unlikely on a fully underground line!) can be applied.
The Victoria Line upgrade included the provision of 47 new trains, manufactured in the UK by Bombardier at Derby. As with all modern metro control systems, much of the equipment is train borne. Key to the train ATC operation is the Mobile Control Unit (MCU) that receives the signalling information to enable the train’s onboard ATP to determine its relevant movement authority. These MCUs are duplicated in each cab to ensure maximum availability.
Continuous transmission of the trackside signalling states is required to ensure that the train emergency brakes may be lifted in support of ATC operation. The driver is provided with an enhanced display panel showing train speed, correct side door enable, target speed, distance to next restriction and any discrete system functions (station skip, code amber, code red, etc).
At the commencement of a journey, the driver selects ATO mode and the train will proceed without further manual intervention to the next station following the pressing of two start buttons simultaneously. If the ATO facility is lost, then the train can operate in Protected Manual Mode that enables the train to be driven at line speed but within the limits of the ATP Distance to Go safety information. If both ATO and ATP systems fail, then the train can be moved at slow speed in Restricted Mode to a station or other access location – see earlier control system philosophy section.
Both the ATP and ATO elements contain maps with all the line information so the trains know exactly where they are and the conditions appertaining to any location. This is vital for door opening to ensure that the correct side is activated. Although the system is capable of having automatic door opening once the train is stopped, the facility is currently disabled and door activation is controlled by the driver. Door closure has a countdown clock to assist drivers in keeping to the timetable. The clock time can be altered for different stations according to the determined dwell time.
If timetable or unexpected congestion occurs and a train is turned back short of its intended destination, the driver will be made aware of this from a lineside route signal. If trains need to have a software update on map information, then at present this will require a whole weekend for the entire fleet to be reprogrammed.
Whilst disruption occurred during the installation and commissioning period with many weekend shutdowns being necessary, the line is now transformed and travellers are enjoying the enhanced service. Additional work and possessions have been necessary to remove the old legacy equipment from the infrastructure but that has now been completed. The new trains are much quieter and have noticeably better acceleration.
Having the control centre and train depot on a single site leads to improved co- operation and, even though some initial problems with reliability did occur, the Victoria Line service looks to have settled down for its next 40+ years of existence. During this time, an increase from 180 to 213 million passenger journeys per year is expected.