Automatic Train Protection (United Kingdom)
Automatic Train Protection (ATP) is a method of beacon based railway cab signalling developed by British Rail. The system is only installed on the Great Western Main Line between London Paddington and Bristol Temple Meads, and the Chiltern Main Line from London Marylebone to High Wycombe and Aylesbury. History Background A noticeable uptick in signal passed at danger (SPAD) instances in the 1980s led to calls for a new safety system to be adopted that would entirely prevent their occurrence; specifically, the report into the Clapham Junction rail crash (itself not a SPAD accident) specifically stipulated that British Rail (BR) was to fully implement such a system on nationwide basis within five years. From the onset, it was recognised that considerable work would be involved both to develop and deploy the envisioned system. Accordingly, in 1988, BR launched a three-year program to develop and deploy this new system, with the aim of starting its implementation by 1992. It was assigned the name Automatic Train Protection (ATP), and was a considerably more comprehensive system than the Automatic Warning System (AWS) that was already in operation at that time. Whereas the AWS system only issued alerts to the train's driver, effectively an advisory arrangement that remained open to failure via human error, ATP would instead be able to take control of the train and override the driver to ensure it was driven in accordance with the signalling, as well as other conditions. As a means of risk mitigation, BR opted to perform two ATP pilot systems, the results from these separate schemes was intended to inform planners on what would be involved in a wider rollout as well as to identify which implementation was superior and thus should be installed nationally. The routes used for the two pilot schemes were London Paddington to Bristol, and London Marylebone to High Wycombe and Aylesbury. Each pilot scheme involved the installation and use of different equipment, nonetheless sharing the same purpose, designation, and numerous other characteristics. The Western scheme used equipment supplied by Ateliers de Constructions Electriques de Charleroi (ACEC), while the Chiltern route was furnished with GEC General Signal-built equipment. Neither of the trial schemes involved systems that had been designed from scratch. The Western route's ATP was heavily based on Belgium's Transmission balise-locomotive (TBL) system, while the Chiltern route's ATP was adapted from Germany's Linienzugbeeinflussung system, known as SELCAB. Both trials proved to be largely satisfactory in terms of their operations; following a comprehensive safety review process, Chiltern's ATP infrastructure system received independent safety assurance and thus changed from being a pilot system to being a regular system that was fully usable. Scale-back At the onset of ATP's development, there was an expressed recommendation to expand its coverage across Britain's rail network within half a decade; at one point, BR's management declared that ATP was to be installed on "a large percentage of its network". Railtrack, the agency that took over the management of Britain's railway infrastructure from BR in 1994, subsequently only