56
SIGNALLING/TELECOMS
Chiltern ATP
obsolescence
PAUL DARLINGTON
I
n a signalling system with lineside signals and fitted with an Automatic Train Protection (ATP) system, a brake application will automatically be applied if a train is going too fast, thereby protecting the train from passing signals at danger. This is achieved by transmitting infrastructure data, including the maximum speed limit, to trains by a communication system. ATP consists of equipment located trackside and on-board trains, with the communication normally delivered by using inductive ‘loops’, beacons or a radio link. Following the investigation into the 1988 Clapham Junction Railway Accident, recommendation 46 of the report required that, after a specific type of ATP system had been selected, British Rail (BR) had to fully implement ATP nationally within five years. This would have been a huge task, but BR instigated two ATP pilot systems – one on the Great Western route and one on the Chiltern route – to help identify an ATP system that should be installed nationally. The Chiltern route was selected for an ATP system based on the LZB system used in Germany. This was developed by Standard Elektrik Lorenz (SEL) and was called SELCAB. SELCAB used inductive
loops to communicate between the track and train on the approach to signals, using loops sometimes several hundred metres long and terminating at the foot of the signal. SELCAB had some adaptions to fit the BR market, which made it a bespoke system and one not used elsewhere. On the Chiltern route, it was fitted between Marylebone and Aylesbury (excluding the Transport for London (TfL) section from Harrow on the Hill to Amersham) and from Marylebone to Anyho Junction on the route via High Wycombe. All the original Class 165 multiple units were fitted with the ATP system, but not locomotivehauled trains. ATP systems may be continuous or intermittent, with the Chiltern system being an intermittent one. Continuous
Rail Engineer | Issue 186 | September/October 2020
ATP systems provide constant communication with the train throughout its journey, but, in an intermittent ATP system, the data is transmitted to the train only at specific transmission points along the track. These are normally at signals and high-risk locations between signals. Intermittent ATP systems are mainly ‘an add-on’ to lineside signals, with their main purpose being to prevent trains from overrunning stop signals. However, the SELCAB system could also supervise train speed for Permanent Speed Restrictions (PSRs) and pre-programmed Temporary Speed Restrictions (TSRs), but not Emergency Speed Restrictions (ESRs) unlike the trial ATP system provided on Great Western route, which was based on the Belgian TBL (Transmission BaliseLocomotive) ATP system.
