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My previous articles in this newsletter column were all related to ETCS, mainly because it made the publisher happy. Happy customers are important, so this is your first takeaway right there in the first paragraph. Hope that makes you happy too, because (you guessed it) happy readers are important to a writer, to me in this case.

Given the name and theme of this column I should really have started off with today’s article. Nothing beats a solid definition at the beginning of writing about something that not everyone may have the same understanding of. So in this article I will explain to you what I mean by ‘High Performance Signalling’, and you are explicitly invited to use this term in your own professional life if you think it has merit.

Besides this overdue definition, I’m also itching to start writing to you about CBTC, the Communications-Based Train Control technology. Why? Because CBTC is arguably the ultimate mainstream technology for High Performance Signalling.

By ‘mainstream’ technology I mean a system that is supported and offered by multiple suppliers, and available globally. This is important for any railway that wants to have a competitive procurement environment with multiple comparable options to choose from. CBTC clearly ticks that mainstream box, and so does of course ETCS.

So what do I mean by High Performance Signalling? And why do I think that CBTC provides that more than ETCS or any other mainstream signalling technology?

I coined that term High Performance Signalling around 2016 because I thought, and still think, that the popular (at least here in Australia) term High Capacity Signalling is unnecessarily narrow. Thinking about the additional benefits besides higher capacity that CBTC offers, I came up with a framework called CARA. A framework is something I use often in my training courses to make it easier (including for myself!) to memorise a list of related things, in this case the main characteristics of High Performance Signalling. CARA is an acronym, hopefully easy to remember as it also a girl’s name, which stands for Capacity Availability Reliability and Automation.

For most railways, higher capacity is their foremost expectation from introducing CBTC, so having the C in first position of the CARA framework makes absolute sense. But there is more to performance than just capacity. The issue here is that if a railway does not focus on those additional benefits they may end up being neglected, with likely inferior project outcomes compared to full focus on all four CARA benefits. (Four letters = four benefits, logical isn’t it?)

The first of the two As in CARA stands for Availability. CBTC should fail less often than any traditional legacy signalling system it replaces. Firstly, because it’s new (and expensive!), and secondly because CBTC is usually more centralised than traditional signalling, and any outage due to a technical failure has much more severe consequences under CBTC. It is therefore very important to design a redundant, fault-tolerant, highly available CBTC system. And once this is done, the higher availability compared to the previous signalling system will be a very tangible and desirable benefit of CBTC.

The R in CARA stands for Reliability. But not technical reliability which is closely related to the availability we already discussed. No, what is meant here is operational reliability, in other words more punctual train services.

CBTC advances this operational reliability in two ways. Firstly, the control of train journeys, including the lengths of station stops, is much more accurate and consistent under CBTC than what is achievable with traditional signalling, so there should be fewer delays and thus better adherence to the timetable to begin with. Secondly, CBTC can also facilitate a faster recovery from traffic disruptions, meaning that trains get back on time quickly after minor delays. This is a real game-changer from traditional signalling where minor delays often grow and accumulate to bigger delays which then may spread out across the network, sometimes causing real chaos for the timetable.

I have heard from several metro railways that talked about their main observations after introducing CBTC that the step change in service punctuality (often called “on time running”) was the most positively surprising and hence most appreciated benefit from CBTC, whereas the higher capacity also gained from CBTC was just “as expected”.

Now to the last letter of CARA and the second A – Automation. CBTC is a technology which provides Automatic Train Control (ATC). The three main functionalities of ATC are Automatic Train Protection (ATP), Automatic Train Operation (ATO) and Automatic Train Supervision (ATS). You can see from all those As that CBTC is literally oozing with automation.

What are the benefits of that? Well, many people think of automation mainly in terms of replacing humans with computers, destroying jobs and livelihoods of railway workers. Unsurprisingly, such prejudice often leads to adversary and opposition to the change induced by CBTC, and often enough to the CBTC technology itself.

I strongly believe that the automation offered by CBTC can be utilised to support human railway staff rather than replacing them. The reduction in human error is a very obvious upside of automation. But wait, there is more.

One of the ‘superpowers’ of CBTC is its capability to regulate train movements, specifically multiple train movements at the same time. This feature often has its own name, Automatic Train Regulation or ATR, but is in fact a function of the CBTC subsystem for Automatic Train Supervision. ATR can, for example, even out the intervals between trains if some are delayed and others on time. This is a useful feature because for a metro railway that relies more on “turn up and go” services than a rigid timetable the consistency of intervals between following trains is often more important than varying intervals to keep the undelayed trains on schedule. Another benefit of ATR can be to regulate out conflicts of train movements, by influencing both trains in a way that separates their arrival at the conflict point and avoids one train being stopped to let the other train pass.

But the real kicker is that the regulating commands that ATR sends to the trains are automatically, precisely and instantly executed by the Automatic Train Operation function onboard those trains. So it is not only ATR, it is the collaboration of ATR and ATO that really hits it off for CBTC.

There are a number of other benefits that could be listed for Automatic Train Operation alone, from energy-saving driving patterns to the removal of driving variability between human drivers. More driving consistency means less need for buffers in the timetable, which can be used for higher capacity, and also improved adherence to the timetable.

So there you have my CARA framework and an explanation what I mean by High Performance Signalling and how it provides more than just high capacity.

A word on ETCS regarding High Performance Signalling. I have written before in this column that the way to improve the performance of ETCS applications is to make them “more like CBTC”. That could mean the addition of ATO, an integrated traffic management system alike the ATS in CBTC systems, and methods for increasing capacity such as cab signalling without signals but with capacity-optimised fixed block sections, or a mix of fixed and virtual blocks to achieve shorter block lengths that support higher capacity. I tend call those enhanced varieties of ETCS “Level 2 plus”, and of course the CARA framework of benefits is applicable to those ETCS applications as well, even if maybe not always to the same extent as for CBTC.

When I introduced my idea of High Performance Signalling on LinkedIn back in 2016 I used the then world’s best sprinter Usain Bolt as an example for the difference between high capacity and high performance. If you fancy reading my thoughts from that time (AFTER you are good with this newsletter of course), check out this article: check out this article on Linkedin

So much for today. If you have any questions on this topic, contact us on the email office@newinsignal.com and you may get them answered in another column of mine that is planned on this website called “Ask the Doc”.

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