London Thameslink ETCS signalling
Challenge
Providing the north-south axis to Elizabeth Line's east-west route through London, is Thameslink, a £6bn nine year refurbishment that completed in 2018.
Stretching from the south coast of England, through London’s suburbs and central districts, and as far north as Kings Lynn by the Norfolk coast, the Thameslink programme brought new, longer trains, resolved some notorious network bottlenecks, and delivered major improvements to key stations, such as Farringdon, Blackfriars and London Bridge, amongst others.
An upgrade of existing infrastructure (some tunnel sections date back to the 1860s) rather than a new build, Thameslink’s transformation was a gradual, incremental process that had to be constructed amidst the capital's functioning network ("like trying to conduct open heart surgery with the patient going about their daily routines", equated one commentator)
ETCS signalling in the Thameslink ‘Core’
Central to the entire programme is the ‘Core’ — a short, double-track section between Blackfriars and St Pancras through which all cross-city services pass. With a new signalling design to cater for up to 24 trains per hour (pervious capacity was 16tph) this section supports service frequencies more akin to that of a metro. And herein lied a major technical challenge.
Most metro systems under construction or refurbishment today would turn to Communications Based Train Control (CBTC) to manage the level of traffic intended for the Core (as, indeed, Crossrail will for its own central section). This is because CBTC is designed for the stop-start nature of metros, using automated control of train movements to allow shorter headways between services.
But as a Network Rail project — and consistent with their commitment to adopt train control technology championed by the EU to bring consistency across Member States — Thameslink uses European Train Control System (ETCS) as its standard for signalling. This is despite preconceptions that ETCS is optimized for regional and national mainline railways and not a metro-style operation.
However, Thameslink has developed the concept of an ETCS railway overlaid on a conventional signalling system to deliver a ‘metro style’ operation. The high capacity is achieved through two new features:
- ETCS allowing the implementation of shorter block sections in a conventionally signalled area, in particular around stations
- The first use of an Automatic Train Operation (ATO) with ETCS on the mainline railway, to allow consistent train driving
Furthermore, by retaining the conventional signalling, a fall back system will be present in the event of ETCS failure.
Approach
Ricardo's role was to develop the safety programme for the project. Being involved from an early stage allowed us to influence the sub-system requirements and operations, not only to achieve high levels of safety but also to ensure performance is optimized.
We started in 2009 with the high-level operational requirements and developed application scenarios to model in detail how the ETCS would work. At the same time, our experts looked at every possible risk to the system’s safe and efficient operation.
We then moved onto the integration aspects, using scenario modelling to identify the detailed sub-system functional and safety requirements, and develop new operating rules and principles.
Results
By using ATO, with the underlying Automatic Train Protection (ATP) provided by ETCS, the core section can safely support 2.5min headways and enable service recovery mode with headways of just two minutes, when necessary.
As the first time ATO has been used with ETCS there were a range of system integration aspects to consider, including the new rolling stock that was introduced in the final stages of the project.
Since 2019, services have been switching to driver-managed automatic control in the central core section, bringing 'metro style' frequencies to a mainline route bringing improved connections through the city for commuter regions to the far north and south of the capital.