The clue to an ETCS-only access

Today, railway networks and their infrastructure managers, as well as the  railway undertakings, are facing the crucial challenge of migrating their signalling and train control systems towards the common European Rail  Traffic Management System (ERTMS), while perhaps also maintaining conventional and mixed traffic operations.

The basic concept of ERTMS, namely interoperable railway traffic within Europe, lacks an economical, straight forward and customer-oriented possibility to migrate the national signalling systems towards ETCS.

Therefore, the UNISIG Change Request 637 (UCR 637) ‘Limited Supervision’ (LS) was given in by SBB and other supporters at the European Railway Agency (ERA) in 2003. Five years have now passed and the sector organisations are still struggling with the challenge of the further deployment of ETCS. Why? The current possibilities to migrate existing signalling systems towards ETCS do not fulfil the needs a migration has to provide – fast, economical and simple.

Requirements for successful migration

What criteria influence a net wide migration?

1. Daily business: LS goes along with it and suits the needs (migration under operation)
2. Interoperability: With LS the ‘ETCS only’ access is guaranteed (SRS 3 available by 2012)
3. Time: LS is the answer for a fast migration towards ETCS
4. Efficiency: Almost no infrastructure modifications are needed (no IXL replacement nor moving of signals)
5. Customer orientation: railway undertakings can keep their own pace regarding the refittment of the vehicle with ETCS equipment
6. Costs: Assumptions and case studies show a possible cost saving factor of 50% compared with a Level 1 Full Supervision implementation
7. Capacity: LS is scalable according to the needs and allows maintaining at least the same network capacity
8. Safety: At least the same safety level  as for the legacy system is guaranteed
9. Operational harmonisation:  With LS technical interoperability  is fully achieved
10. TSI relevance: LS is expected to be legalised by the end of 2012 (SRS 3 TSI relevance)

At least for these ten important issues, ETCS L1 Limited Supervision can be the clue to a successful migration strategy.

Allowing ‘ETCS only’ trains and others

Switzerland and its infrastructure managers (IM e.g. SBB, BLS) are committed to achieve network-wide operational interoperability in order to support the ETCS corridor implementation in collaboration with any other neighbouring national railway or network operator. As an intermediate step towards the fully harmonised operation of railway services, the Swiss IM’s are willing to establish the technical interoperability in order to support the railway undertakings’ benefits and reduce technological constraints (e.g. lifecycle of  a product).

In fact the goal is to:

• Enable ETCS-only trains to access the whole network
• Maintain access to no-ETCS, national-system-fitted trains

The biggest advantages of ETCS come only to the effects, when whole lines, areas or networks are ready for ETCS access and operators can access the network with a pure ETCS train or vehicle. Compared with today’s situation, where a train needs to have up to four different train control systems on-board, railway undertakings are expected to save up to 75% of investment and operational costs for onboard train protection systems.

The mode ‘Limited supervision’ (LS)

The ETCS mode LS provides a trackside possibility to operate trains either as fully ETCS equipped units or as non-ETCS equipped units since the trains run on the same infrastructure as today.

LS avoids compulsory investments in equipping train fleets and infrastructure because it is compatible with both ETCS and existing national systems. Therefore, SBB has raised the Change Request 637 ‘Limited Supervision’ to the ERA, in order to develop such an ETCS application. Meanwhile, the efforts of SBB go beyond simply raising a change request. Because of the delay in the publication of the next system requirements specifications (SRS), the so called baseline 3 (B3), SBB started to develop the mode LS by financing and cooperating with the UNISIG industries as well as with two partner railways (DB AG and RFI) under the control of ERA and the ERTMS Users Group.

As it is shown in Figure 1 on page 15, LS will be ready to be incorporated in B3 on time. According to the new Memorandum of Understanding between the DG TREN and the sector organisations (ERA, CER, EIM, UNISIG, …), a functional change has to have an agreed solution by the end of September 2008 at the latest. The fact that LS will become a mode in SRS 3.0 will provide a migration alternative to a couple of railways (e.g. Croatia, Rumania, DB AG, etc.) and will therefore push forward the migration of the railways network and operators towards ETCS. Experts are quite certain, that LS will provide a migration step for other railways too  (e.g. France, Italy, and others) and support the future deployment of ETCS in Europe.

SBB is not only Switzerland’s biggest Railway, the SBB Infrastructure Division is also contracted to be the ERTMS System Authority for Switzerland. This fact includes the responsibility of defining system management processes as well as supporting interoperability according to the TSI.

How does LS work?

The wording ‘Limited Supervision’  means that onboard supervision is not applied to each and every block section, danger point or speed limited section.  This implicates that on the DMI not  all relevant signalling data are shown  (e.g. Circular Speed Gage (CSG),  Planning Area) and the driver is forced to watch the lineside signals. Therefore, Limited Supervision is different from  Full Supervision (FS) and doesn’t assume the same safety level. This (if appropriate) provides potential investment savings on engineering and production costs and is less restrictive on capacity issues. The supervision of such a danger point depends on the defined hazard level, usually set by the National Safety Authority. However the maximum speed allowed (MRSP) is supervised by the train control system.

Limited supervision is not cab signalling and thus it depends on the line side signalling and its associated functions (e.g. KVB, PZB, ZUB, others). The primary safety responsibility is given to the driver and not to the Automatic Train Protection System (ATP). The ATP, as mentioned before, is active in the background and intervenes only in case  of danger (see Figure).

LS provides an economical and smooth migration approach towards ERTMS cab signalling: Instead of equipping each train set or loco with ETCS systems and using an STM for  non-ETCS lines, ETCS standard equipment is put on the trackside first. Thus, the migration towards ETCS starts on the trackside. The ETCS equipment, namely Eurobalise, Euroloop and LEU, provides the national functions (e.g. PZB, ZUB, Signum, etc.) by using the packet 44.

Later, according to the business needs of the infrastructure managers, the railway undertakings or the public body, the hardware can be upgraded with the full ETCS telegram. This enables the use of ERTMS by an operator with pure ETCS vehicles as soon as a dedicated line or corridor achieves to be fitted with the full ETCS information (see Figure 3).

After finishing the migration phase,  the infrastructure provides for ‘all’ kinds of rolling stock appropriate train control functionality. Pure ETCS and non-ETCS vehicles can operate on such a network without additional investments.

The absolute advantage of LS results from operational aspects, the LS set-up on the existing systems and therefore on the applied safety levels as well. Capacity on the other hand, is, inversely proportional to safety. Thus, by defining the safety level, the maximum capacity is implicitly given for a line or topology as well. Therefore, ETCS LS doesn’t reduce existing capacity and safety requirements to the network as an application in FS mode (especially L1) would suffice.

The operational mode LS could be compared with the operational mode ‘On Sight (OS)’ with one important difference. Balise and loop information are not taken into account when operating on an ETCS network in the OS mode. In mode LS, Balise and Loop information is taken into account. The information shown on the DMI is almost the same (except for a few details). A new mode icon will be defined as well as the screen design in total (see Figure 4). Colours and arrangements will follow the DMI specifications.

Motives to migrate towards ERTMS

The infrastructure managers and operators have different reasons to migrate their train control system to ETCS:

• Old systems become obsolete
• European law (TSI) dictates the implementation of ETCS
• Corridor applications (cross  border traffic)
• Attractive network access

Furthermore, SBB is clearly of the opinion that the future of ERTMS and its success is depending on the costs faced by the railway undertakings to operate fleets with ETCS. Total costs of train borne system modifications (software) are a multiple of what system modifications will cost on trackside installations. With this currently stagnant system development process, railway undertakings will not invest in ETCS. Neither tomorrow, nor the day after tomorrow. This is one major reason to shorten the migration period as much as possible and provide ETCS access for the RU’s as fast as possible. Reducing onboard systems is a key factor of success for the railway undertakings to invest in ETCS!

Why does SBB not use STM?

By using STM as a solution for the migration, railway undertakings would face the same challenges as they do today. Since the European Railway Network is a ‘wild’ puzzle of dedicated ETCS lines, end-to-end production would not be possible. To pass those sections which are not equipped with ETCS yet, the railway undertaking would have to develop an STM for each infrastructure or network section it passes with a different train protection system (e.g. PZB, ZUB, KVB, etc.). Thus, the operator ends up with expensive multiple onboard systems on the vehicles and limiting space, operational flexibility and providing no benefit and certainly no feasible business case. By contrast, the LS migration strategy focuses on a hardware solution which has to be developed only once. The Eurobalise Transmission Module (ETM) is basically a standard Eurobalise antenna, mounted on the underside of a vehicle and able to read Eurobalise information. This implementation is comparable to a country specific packet 44 application (see Figure 3). The ETM solution is in operation since early 2000 in Switzerland with promising performance (system reliability).

Conclusions

The core aspects of a migration towards ERTMS, address the core business needs of railway undertakings and infrastructure managers. It ensures smooth and sustainable evolution towards  operational interoperability. LS allows infrastructure managers to act with a customer-oriented focus.

LS is clearly minimising the investments by using the ERTMS  standard (baseline 3 or higher) and anticipates an even better net-present-value for infrastructure managers that can access external ERTMS funding for  this investment.

A fast, economical and simple migration towards ERTMS generates the biggest benefit for the railway undertakings as for the infrastructure managers as well.