Network Rail Scotland is replacing the current track-to-train radio communication system and interface to the train control system on the West Highland lines to Oban, Fort William and Mallaig and the Far North lines to Kyle of Lochalsh and Wick/Thurso.

These lines pass through spectacular countryside. The mountains and moorlands of the landscape mean that, despite its beauty, it represents a major challenge to the engineering design and construction of the communication system.

The system is known as the Radio Electronic Token Block (RETB) and comprises the radio system, the signalling Solid State Interlocking (SSI) and equipment located on-board trains. It is a ‘Class B’ system under the Control Command and Signalling sub-system technical specification for interoperability (TSI).

The RETB Next Generation Project, described in issue 125 (March 2015), is more than a renewal of the current system, as it also mitigates the risk of radio interference when European frequencies for digital television change in December 2015. This means that the current ‘Band III sub-band 2’ radio equipment will be replaced with new radio equipment operating on ‘Band III sub-band 1’. The project’s remit also involves the development of replacement on-train, depot, engineering and trackside equipment.

Operational trials and implementation are planned for completion before the end of 2015 to meet the frequency change deadline.

Conformance approval services

Network Certification Body (NCB) is working closely with Network Rail providing conformance approval services throughout the project lifecycle. Initially, this was safety verification under the Railways and Other Guided Transport Systems (Safety) regulations (ROGS) which transitioned to supporting the project under the Common Safety Method for Risk Evaluation and Assessment (CSM-RA) regulation.

NCB provides safety assessment reports at agreed points in the programme, assessing against the requirements of CSM-RA by checking that:
» There is evidence that the system being changed is adequately defined;
» The process for hazard identification is robust and complete (classification of hazards is justified and the three risk acceptance principles have been correctly applied);
» The hazard record contains the right information about the hazards, associated safety measures, and responsibilities (and that hazards and the safety measures are closed and validated);
» The processes used for managing safety and quality meet the requirements of Network Rail’s Health and Safety Management System.

A positive report from NCB will support Network Rail (as ‘Proposer’ under CSM-RA) in providing a safety acceptance declaration under CSM-RA that all identified hazards and associated risks are controlled to an acceptable level.

This is vital, as it provides the basis for the Proposer’s ultimate decision about whether to implement the system changes.

Written by Richard Feasby, Senior Infrastructure Conformance engineer at Network Certification Body.