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Eugene Broderick GradDipRailSig AMIRSE

Laing O’Rourke Australia

Stephen Lemon MSc MIEAust CPEng RPEQ MIRSE

Laing O’Rourke Australia

The Docklands Light Railway (DLR) in London opened in 1987 with an ATP/ATO signalling and control system, with no mainline signals, and technology that included VDU-based train control, SSI interlockings, reed RT-type track circuits, and audio frequencies injected into the running rails and cable loops, to provide 'authority to proceed' and 'speed monitoring' functionality respectively.

As a result of the need to increase the capacity of the railway, both in terms of the geographical area covered and the throughput of trains, a new ATP/ATO system was introduced during the mid 1990s, based around moving-block  Communications-Based Train Control (CBTC) technology. The signalling and control functionality of this CBTC system relied upon continuous data communication between the trains and centralised interlocking and control systems via a series of trackside loop cables, supported by an underlying system of axle counters.

The moving-block system was first implemented on a new extension to the railway, and subsequently as a replacement for the existing fixed block system on the entire railway, and it has been subject to a number of major and minor upgrades to the equipment and software since that time.

From the early days of the DLR, there were issues associated with the operation and maintenance of the signalling, control and communications systems, which were predominantly electronic and software-based, at a time when the experience of staff in the UK rail signalling industry was largely based around more prevalent mechanical and electrical systems.

With the transition to a more complex CBTC system, the technical and operational issues were compounded. In particular, the ongoing upgrades to the system required robust processes to manage the impact of changes, with a focus on strict configuration control, systems assurance and approval.