There is an ongoing programme across London Underground to install this equipment on all non Automatic Train Operation (ATO) passenger trains; ATO trains already a Runback Protection System.
It's purpose is simple - Runback Protection System (RPS) is train borne equipment that applies the brakes and brings the train to a halt if the train moves backwards more than two metres, unless the train has been placed in reverse.
Before looking at the actual equipment, why has it been decided to install this system? In July 2000 there was an incident at Chalk Farm on the Northern Line where a train rolled back for about one kilometre. Following an assessment of the incident it was found that it is possible for a person to be asleep for up to two minutes and that they may not loose muscle tone and not be aware that they are asleep. Therefore, the deadman device in itself is not sufficient in itself to prevent such an occurrence.
The visible components are a modification to the leading offside bogie which has the sensor installed to the centre of the wheel in place of the normal axlebox as can be seen in the following image.
As can be seen there is a cable running from the unit which leads through to the RPS Cab Interface Panel as in the next image.
This unit includes a data logging device which records any relevant events and which can be downloaded for examination. Normally this will be used for maintenance fault finding purposes, but could also be used for incident investigation
Of course, the unit is connected through the train's brake system to activate the brakes if appropriate. There are also set procedures to cover eventualities such as legitimate activation and should the 'self monitoring' of the unit report a fault. As can be seen there is an isolation switch (the sealed switch to the right of the unit) and a fault indication lamp to the left of this.
In the event that a fault develops with the system that the Train Operator is unable to clear, the train will be withdrawn from passenger service and taken empty to depot for the fault to be corrected.
Although the photos I have used above are from a D78 Stock, the installation on the C69/77 Stock is very similar; there are a few procedural differences, but the overall purpose of the installation is the same.
The following give some comparisons between the installations on different rolling stock. Thanks to Chris Cobley for the images of the 73 Tube Stock and the A60 Stock equipment.
The installation on a C69/77 Stock .
The installation on an A60
Installation on a 73TS - note the difference in the design, though the function is identical