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Railway interlocking goes digital

Thales’ interlocking keeps passengers safe. It is also one of the key building blocks of railway digitalisation. 

Interlocking systems are the hidden heroes of railway transportation. Few passengers are even aware of their existence. Yet every train journey depends on interlockings – and it’s thanks to interlockings that railways are one of the safest ways to travel. Alexandre Da Silva, Product Line Manager and Frédéric Aupépin, Product Line Architect, explain why Thales’ digital interlocking is so important. 

First of all, what is interlocking and why does it matter?

Interlocking is the bedrock of railway signalling. The purpose of interlocking is to provide trains with safe routes and keep them a safe distance apart so there is no risk of collision. It acts like a brain, verifying instructions and orchestrating the operation of signals, points, level crossings and other critical assets. Interlocking is a SIL 4 system, which means it must provide the highest standard of safety integrity.  


Can you tell us about Thales’ interlocking?

We provide our customers with a fully-integrated digital interlocking solution. This performs two functions. First, it processes safety-critical signalling rules using a centralised logic system. Second, it provides a way to control field elements, such as points and signals. This is achieved using Smart Field Element Controllers. This makes our signalling system both modular and highly scalable. Importantly, it provides our customers with the freedom to organise the control of field equipment in a way that best suits their operational needs, now and in the future.


Where can it be used?

The beauty of our digital interlocking solution is that it is truly universal. It is used by railway infrastructure managers across Europe, Asia and Africa – so it really is interlocking without frontiers. This is possible because it can be easily customised to satisfy the national requirements of any country, without the need for specialist software development skills. This is important, because signalling rules vary from one country to another. 


What type of railway operations can you support?

Our digital interlocking can – and does – support every type of rail operation: high-speed lines, including ETCS Level 2, conventional main lines, suburban routes and secondary lines. It is also used on metro systems, including some of the busiest in the world. So there are absolutely no limits on where you can deploy Thales’ digital interlocking solution. 


How is it deployed?

Our solution can be deployed in the conventional way in signalling centres or technical equipment rooms. But thanks to TransVital™, our new hardware-independent safety platform for SIL 4 applications, it can also be deployed in a data centre and soon on a private cloud.


How easy is it to integrate with signalling equipment from other suppliers?

It is designed to be used universally. The solution conforms to EULYNX standardisation principles, which means that it can be integrated with different subsystems, including those manufactured by third-party suppliers. Interfaces are standardised. This boosts flexibility and contributes to lower lifecycle costs.


You mentioned Smart Field Element Controllers. What are they for and how do they help?

Smart Field Element Controllers are an integral part of our digital interlocking solution and they deliver a lot of benefits for our customers. Their purpose is to convert digital commands from the centralised logic system into electrical power outputs, which are used to operate point machines and illuminate signals. 

A key point here is that field element control is best carried out locally – as near to the points and signals as possible. Traditionally, the element control function was much more centralised, resulting in very long and expensive cable runs. But with Smart Field Element Controllers, control is local, so less cabling is needed.       

One of the benefits of decentralised field element control is flexibility. For example, you can create logical geographical groups of signals and points controlled by local field element controllers. This not only speeds up deployment, it makes it much easier to make changes later on. For example, if you want to add a new section of track or change the layout, you can make the alterations in just one zone – independently – without affecting the whole configuration. So it causes much less disruption. It is also much easier to maintain.


Does this mean fewer delays for passengers?

Yes. One of the key needs our customers have is improving availability – in other words, minimising or eliminating downtime on the network. Infrastructure managers need ways to boost the growth of rail traffic. And with the rail market being opened up to greater levels of competition, there is also a need to support new passenger and freight operators. Network availability is vital. To ensure this, you need interlockings that you can adapt, expand and maintain – without disrupting rail traffic.


Can smarter signalling improve environmental performance?

Yes. In the context of signalling, sustainability can be improved by reducing the amount of maintenance-intensive trackside equipment, and by cutting down on the use of copper cable. Using less cabling is not only better for the environment, it is also a big cost saving for infrastructure managers – particularly with copper prices at all-time highs.  


How do you reduce cabling in practical terms?

Local control is the key. Instead of having multiple copper cables between the centralised logic system and the trackside, you only need a single fibre optic control cable to link the logic system with the local Smart Field Element Controller group. All you then need are relatively short stretches of copper power cable between the element controller and the points and signals. This is a huge saving, amounting to hundreds of kilometres of copper cable. 

Sustainability is not only about reducing the use of copper cables. It is also about system design and lifecycle impacts. By centralising the logic system, we are able to reduce the consumption of raw materials and lessen the need for transport to remote sites. The need for trackside buildings is also reduced. All of this contributes to lower emissions. 

In parallel with this, there is a need to ensure maximum reuse of existing assets when signalling is upgraded. This matters because a large rail network can have 200,000 or more points and signals. Many of these assets will have decades of useful life ahead of them. Our approach is to provide easy interfaces to enable the maximum reuse of field equipment. Again, this means less waste.  


What about maintenance?

Digital interlocking systems produce huge amounts of valuable data. Our customers can use this not only for real-time health monitoring, but also to support predictive maintenance. There is also support for remote maintenance. For example, our remote upgrade capability means you can easily update software for Smart Field Element Controllers from a central node – with no need to go out into the field.


How important is cybersecurity in signalling systems?

It’s absolutely critical. Cybersecurity is one of Thales’ core competences and all of our solutions are “Cybersecured by Design”. This means that cybersecurity is built into the solution from the design stage. On top of this, we support our customers with cybersecurity maintenance services throughout the lifetime of their systems. 


What does the future have in store?

First, there are going to be big changes in the way that signalling is delivered. For example, Thales is developing ways to link Smart Field Element Controllers with the Internet of Things (IoT) using 4G and 5G radio links. This will eliminate the need for data cables between the centralised logic system and the trackside, adding greater flexibility, speeding up deployment and further reducing costs. 

In parallel with this, we are going to see greater and greater integration between the centralised logic system and the trains themselves. This will make it possible to achieve huge reductions in trackside equipment, such as train detection systems and signals. To do this, Thales is bringing together technologies such as Automatic Train Operation (ATO), Traffic Management Systems, advanced onboard positioning systems and digital maps. These are the technologies behind autonomous trains.  

We believe that these developments will transform the passenger experience in terms of punctuality, capacity and reliability. And not only on the fastest and busiest lines. Digital technology also opens up the possibility of “frugal” signalling, paving the way for reliable, cost-effective operations on secondary regional lines as well.