PSA: understanding the CBTC design and maintenance Challenges

BART project impresses with its large-scale target of the full system transfer (131.5 miles) to CBTC by 2030. CBTC becomes an elegant continuation of the history of multiple railway networks, some of which originated in the 19th century. The foreseeable destination of such a history usually comes to GoA4. Well, the future belongs to CBTC without exaggeration, but there is still no single standard for CBTC equipment communication and it is not a fact that they’ll ever appear. This issue is under hot discussion since single requirements promote supplier-independent design and maintenance of the CBTC system from the one side, but standardization slows down the evolution from the other side.

The challenge of compatibility, interchangeability, and interoperability is much wider than it seems and the solution largely affects both CapEx and OpEx. Actually, this is what we struggle with during the whole CBTC system lifecycle. So now, CBTC's introduction is a joint responsibility of rail authorities and suppliers to consider all possible compatibility aspects to ensure safe and reliable transportation and bolster the potential for further network development. In PSA, we’ve been working on CBTC implementation projects for over 15 years, and we want to share our engineering view on urgent and prospective challenges for you to define the most elegant strategies for CBTC design and maintenance.

Core Aspects of CBTC Compatibility
Mostly, CBTC is an “above level” of the signaling system. Lots of rail authorities decide to leave conventional as a fallback signaling system, which definitely increases the safety level. Tie-ins are crucial to connect the railroad sections under conventional and digital signaling systems for continued operation and to provide system transfer during commissioning procedures. Moreover, CBTC can comprise ATP, ATO, and ATS subsystems, which widens the connectivity surface.

Factors that define the scope for compatibility:

1. Overlaying the legacy signaling on the wayside
Basically, it’s not rocket science to connect the legacy relay-based system with the modern microprocessor-based system when having skillful signaling engineers to build schematic diagrams. The headache comes with legacy-new microprocessor-based systems connection through the obsolete protocols. Here, engineering resources gain even greater importance to correctly simulate and update systems. These upgrades often require additional dedicated transmission modules for interfacing with legacy, which commonly complicates the system.

2. CBTC delivery for dispatching
A CBTC product with dispatching functionality suggests top-robust communication with the wayside equipment and real-time data transfer. By experience, such “multi-layer” work requires sustainable development and support efforts. HAL (intermediate layer) intervention may be required to provide compatibility, optimization for the processor usage, or memory issues resolution – there is enough to deal with. Comprehensive expertise in rail system development is required here to ensure impeccable end-to-end supervision.

3. Interoperability for system components
Since CBTC is a concept first, it doesn’t provide for compulsory products or vendors. The market is full of incompatible patented products that are not interchangeable by default. When diving into equipment design, some rail-related peculiarities may also cause incompatibility over time.

Compatibility for CBTC Equipment Components: Risks of the Future
As with all the rail signaling systems, the CBTC-based system is intended for decades, which will inevitably lead to some standards becoming obsolete, even within one-supplier systems. PLCs, their parts, and interfaces all turn into legacy products over time and cause compatibility issues.

With the maintenance process and new components addition, legacy can start to behave unpredictably. It would seem that they can be simply replaced, but are you sure to find these legacies on the market in 20-30 years? It is hard to predict how painless will the CBTC maintenance be at such time distances, as well as to calculate the demand for these outdated systems in the railway market since their replacement is often needed suddenly.

For now, let’s take an SD card. This standard is at the top: widespread and used around the world, but who can guess its position in 20 years? This is exactly what happened with PCMCIA – a widespread standard for memory cards typically used for laptops and PLCs in the early 00s. Today, it’s out of the requirements for modern digital systems, being incompatible with them. You hardly find a ready-made replacement card in the market, which requires custom engineering to comply with complex systems, such as rail signaling. In this case, you won’t be able to avoid the involvement of various suppliers.

Naturally, the top-notch standards of today will be replaced with new and more efficient ones. The fate of legacy technologies as well as their behavior under modern standards is a puzzle. The best thing to be done here is to develop forward-looking strategies for CBTC maintenance with a great share of customization activities.

Updates, Simulation, and Testing of CBTC
CBTC is a flexible system that is designed to adjust to the conditions, needs, and standards of a specific railroad. Any infrastructural upgrade, like adding a new junction, provides the system with new functionality that also introduces incompatibility risk. The same applies to equipment upgrades, i.e. changing the configuration of the control unit or adding a more powerful processor.

Thus, multiple system updates are inevitable both before and after commissioning – during the whole lifecycle. It concerns both hardware and software components of interlocking, ATP, dispatching products, and so on, through a modular design. Every time after updates, we have to validate that one module did not affect the functionality of the others. Any tiny deviation such as an increase in the response time is critical here.

This is what we are likely to face in the foreseeable future. Thus, advanced simulation technologies are becoming vital to validate every interlocking scenario under new system configurations. Together with enhancements for signaling tools, it is worth developing forward-looking strategies for continuous compatibility testing to ensure the system's correct operation.

CBTC Predictive Maintenance – Protecting Against Future Challenges
Generally, compatibility issues are revealed before or right after system upgrades, but sometimes a component fails during operation, which increases the risk of a signaling failure. This is one more reason to implement a predictive maintenance approach to railways.

Predictive maintenance is a cutting-edge approach for advanced industrial systems, which relies on the detection of the very first signs of an upcoming malfunction long before it comes. This technique allows for planning only relevant maintenance activities in advance. First, it can be successfully applied to level crossings.

By equipping the level crossing for continuous data acquisition and transmission while passing it through the analytics tool, we’ll gain a precise prediction of the failure, which helps avoid queues and dangerous situations on level crossings. Second, wayside controllers can be equipped correspondingly. Despite diagnostics on board, you should deliver more sensitive data to provide precise predictions.

The complexity of the CBTC may complicate the PLC data acquisition and storage as well, which would require additional embedded memory. However, there is nothing extraordinary about building analytics models for such cases – it’s only a matter of the relevant data collection and time required for neural network training. It’s fair to assume the wider adoption of IoT and AI technologies for the rail industry in the next 20 years.

Summing Up on CBTC Interoperability

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