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the rail engineer • September 2013
of the tunnel killing forty-three people. On the national system, the risk was addressed by adjusting the aspect sequence leading to a terminal platform. Originally, at many terminal stations, the signal authorising a move into the platform would display a green aspect. This was changed to maximum single yellow thereby ensuring drivers would receive an AWS caution before reaching the buffer stops. The provision of TPWS buffer stop OSS closes out the residual risk.
Tilt Authorisation and Speed Supervision (TASS)
Driver’s Reminder Appliance (DRA) Cuts traction power. This was introduced into the driving cab from 1998 as a measure to try and reduce ‘ding-ding and away’ type SPADs. It is not connected to the signalling system and requires the driver to operate it in a proactive manner when a train is held at a red signal. It consists of a switch on the driving desk which when pressed or pushed down, activates the device into ‘set’ mode. The switch displays a red light when set. This prevents the driver taking power. Reset is achieved by pulling up the switch/button.
Enables tilting trains to run at higher speeds than non tilting trains, where authorised to do so. TASS has been installed on some sections of the West Coast main line (WCML) and cross country routes to enable tilting trains such as Pendolino Class 390 and Voyager Class 221 to run at enhanced permissible speeds providing the tilt mechanism is functional. It also prevents tilting where clearances are restricted. TASS is a more sophisticated system than was originally provided for the tilting Advanced Passenger Train (APT) on WCML. C-APT (Control-APT) consisted of passive transponders in the four foot coded with the line speed. These were interrogated by the trainborne equipment to give the driver a digital speed limit display. Although development of the APT came to an end in the mid 1980s, some transponders are believed to still be in situ. TASS uses Eurobalise passive transmitters mounted in the four foot which define the areas over which each train may safely tilt. Speed profiles and tilt authorisation data in ERTMS packet 44 structure is received by the trainborne equipment. The speed of the train is continuously supervised and enhanced permissible speed authorised providing the carriage tilting mechanisms are healthy. The cab ‘speed supervised’ blue light confirms tilt systems are working, balises are being read and the speed supervised according to the profile for the type of train and location. The driver may run at the enhanced permissible speeds that are displayed on lineside signs. TASS intervenes when overspeeding is detected, sounding a warning and slowing the train by 25mph before allowing the driver to continue as a non-tilting train.
European Train Control System (ETCS) Provides cab signalling and train protection functions. The Cambrian lines pilot scheme has previously been covered in depth in the The Rail Engineer. The national project is now moving ahead with a Hertford National Integration Facility (HNIF). Kit from several suppliers will be tested on a five mile section of the Hertford loop prior to national roll-out. A Class 313 EMU has been converted into an ETCS laboratory. In addition to the various train protection systems described above, there are still some others used in the UK. Such systems are used on HS1, London Underground, and metro style railways/tramways in the UK. Perhaps they will form the basis of a future article in The Rail Engineer.
Trainstops Halts a train that passes a red signal. Mechanical trainstops are used on lines over which London Underground trains operate and on a few other lines with a metro-style service. A trainstop is mounted near the signal and the arm is raised when the signal is at danger. When the tripcock on the train is engaged by a raised trainstop arm, a brake application is automatically initiated.