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The secret of easier metro upgrades

Installing high-capacity digital signalling on metros is one of the best ways to boost passenger satisfaction. How can deployment be made easier?

When it comes to improving the performance of existing metros and urban railways, one of the most effective steps an operator can take is to replace traditional signalling with Communications-Based Train Control (CBTC).

CBTC is transformative. Benefits include more trains per hour, faster journey times and enhanced reliability for both operators and passengers. Faster recovery from disruption is an added benefit. All of this contributes to increased passenger satisfaction, loyalty and ridership.
On top of this, CBTC delivers efficiency gains and opportunities for lifecycle cost savings. These are achieved through new ways of working, including the modernisation of operating methods and maintenance practices. 

Switching to CBTC can also save energy. This is a key consideration for operators looking for ways to cut power bills and reduce carbon emissions. There are wider benefits too: high-performance rail transport provides an attractive alternative to car journeys, cutting congestion and enhancing the quality of life in cities.  

Deployment without disruption

Installing new signalling on a working railway is a complex business because the operator has to ensure minimum network disruption. In fact, it’s such a delicate and complicated operation that it’s sometimes said to be like carrying out open-heart surgery while the patient is running a marathon.

Deadlines add to the pressure – particularly if new signalling needs to be ready in time for a major event, such as the Olympic Games. So how can deployment be made easier?

Two factors have a huge impact on how easy the deployment will be. These are the choice of CBTC technology and the migration strategy. Let’s take a look at these in more detail.

Choosing the best CBTC solution 

One of the big decisions facing operators of existing (brownfield) lines is whether to deploy “pure” CBTC, or to choose a more complex “overlay” solution, which combines CBTC with conventional interlocking and train detection. Pure CBTC is easier to deploy, requires less equipment and is more reliable in the long run. Most operators now opt for pure CBTC.

Another factor is the maturity level of the proposed solution. Is the CBTC system offered by the supplier the best one for an existing line? Some CBTC systems are better suited to greenfield (new) metros. There is a strong case for choosing one that already has a track record as a resignalling solution – above all, one that is purpose-built to be migration ready.

Migration strategy

The migration strategy sets out how the CBTC deployment will be carried out, and it is based on the operator’s performance requirements and technological preferences. Key elements of the migration strategy include:

Rollout methodology – there are three possible approaches. Zone-by-zone migration is the most popular. A benefit of this approach is that it provides the operator with the freedom to choose where to start resignalling. Most operators opt to begin with a section of line that is less heavily used, for example, at the fringe of the network.

Another approach is one-shot migration with the entire line going live at once. The benefit is that interfaces between CBTC and legacy signalling are not required. The risk is that it leaves little room for manoeuvre if adaptations are needed or the plan needs to be changed. A variant of this approach is to use time migration, with CBTC initially used only during non-critical times, such as afternoons, late evenings and weekends. 

Track access – one of the biggest challenges is getting access to the track to install new equipment. With many metros shifting to 24/7 operation, finding slots is getting harder and harder. Workarounds are possible. One approach is to establish temporary bi-directional operations, so engineering teams can work on one side of the track while trains run on the other. This approach has been used successfully on one of the world’s busiest metros.

Possession planning – this is the key to making the best use of scarce track access time. Engineering works are carefully structured to ensure the railway is restored to normal at the end of the shift, so that the morning’s services are not delayed. A 50/50 approach is the most effective. The first half of the shift is devoted to installation and testing, while the second half is completely focused on returning the system to its original state.

Migration accelerators

New tools and technologies are also helping to minimise disruption during resignalling. These include lidar surveys (to boost the speed and quality of trackside measurements), connected workforce tools (real-time information sharing with trackside teams), remote database and software uploads (managed from a central location) and shadow mode monitoring (for testing critical systems during normal operating hours).

Looking ahead, the transition to LTE and 5G paves the way for cable-free CBTC. And innovations such as Thales’ Next Generation Positioning promise further reductions in trackside equipment and faster migrations.

How can Thales help?

Thales knows more about upgrading existing lines than any other supplier in the market. We were the first to deploy CBTC for resignalling back in the 1990s. Over the past 30 years, we have accumulated vast experience with deployments on some of the world’s busiest lines in cities including London, New York and Singapore.   

Our expertise is underpinned by our ability to adapt our solution to any type of operating environment, and to equip any type of train for CBTC operation. For cities preparing to meet future demand, Thales’ SelTrac™ CBTC provides the optimal solution for a seamless transformation – no matter how large or complex the project.


Download our white paper to discover more about Thales’ approach to CBTC deployment