Signaling X: Siemens shows metro control CBTC on conventional servers
From Braunschweig to the Singapore test ring: Siemens has shown its Signaling-X system for railways, which runs on standard servers, and Heise Online was there.
Visiting the Signaling X demonstration in Singapore in November 2025.
(Image: Siemens Mobility)
The system's goal is to control and monitor metro systems, up to fully automated ones, according to the Communications-Based Train Control (CBTC) standard. Due to its concept, the system is already geo-redundant in its minimum configuration.
Naturally, this could not be demonstrated in Singapore, as the test ring is only about 3 km long anyway. Accordingly, all three servers were housed in a 19-inch rack.
The third server is for redundancy
For safety reasons, two Signaling-X servers must always be in operation simultaneously, with the third serving as redundancy. However, all three servers can be distributed arbitrarily. Therefore, if a server fails due to a power outage, flooding, or fire, operations can continue. However, geo-redundancy only offers limited protection against larger-scale events such as earthquakes. In such cases, the transport operator would have other problems anyway.
The precursor to this geo-redundant concept is, incidentally, the implementation of digital signal boxes in Norway for Bane Nor, which Heise Online previously reported on extensively.
At the customer's request, more servers or the provision of additional servers would also be possible. Synchronization should be completed within a few minutes, according to Siemens.
Proprietary hardware can sometimes be dispensed with
According to Siemens, implementing server-based interlocking operations with Signaling X offers several advantages. Thanks to its basis on standard network components, the classic range limitation no longer exists. An Electronic Interlocking System (ESTW) has a range of only 6.5 kilometers. Of course, there are still interim solutions. It doesn't have to be Siemens' Signaling X to operate signal boxes at greater distances. In Germany, for example, these are Digital Signal Boxes (DSTW).
At the same time, a lot of space is saved in the server cabinets. The installation at SRTC clearly demonstrated this. The four well-filled 19-inch racks with the old CBTC equipment were replaced by a barely filled Signaling-X rack.
(Image:Â Andreas Sebayang/heise medien)
However, the space saved shown is not realistic. Siemens still expects some components that cannot be easily replaced, and network switches, for example. In general, the space saving is still significant, as the old PIM50 modules for signal inputs alone take up a huge amount of space in the rack.
Smart Object Control
However, not everything can be fully digitized and centralized. There are old components on a line that are intended to remain in operation. In Singapore, Siemens Mobility demonstrated a new solution for digitizing old trackside hardware: the Smart Object Control Box.
(Image:Â Foto: Andreas Sebayang/heise medien)
In an initial implementation, Siemens intends to connect switch drives to the Signaling-X servers via Ethernet. To do this, only the power connections need to be routed into the box. However, this must first be tested in Siemens' signal factory in Braunschweig, as there are numerous different switch and switch drive models.
As a side effect, the box can also perform power measurements and detect, for example, increased power consumption – often an indication of impending switch maintenance. The switch is the simplest use case for the new box. However, in the future, objects such as platform screen doors, retractable cable systems, axle counters, or even old signals could be connected to such a box and integrated into Signaling X, according to Siemens Mobility in conversation with Heise Online.
Migration to Signaling X should be easy thanks to fallback
Partial implementation is also of interest to transport operators. Signaling X can, for example, only be used on a part of a line. An operator could migrate a handful of stations on an outer branch to the new system. Since the switchover can be carried out quite quickly, which Siemens also demonstrated to its customers in Singapore by pulling cables, a test operation, for example at night, would also be possible at first. Switching back to the old system as a fallback is also possible in case of problems.
On the test ring, the migration was technically quick according to Siemens. After everything was tested on a digital twin in Braunschweig, the new equipment had to be transported to Singapore. Before that, Siemens Mobility had installed the old CBTC system. The actual conversion took about a day.
In a customer scenario, of course, practical test and acceptance runs are added here. How long a system is down depends on the respective supervisory authorities. Incidentally, nothing had to be changed on the train, which was already CBTC-compatible, for Signaling X.
Trains require computing power
The system also offers some advantages when expanding the infrastructure retrospectively. The control and monitoring of train operations are the main burdens on the servers. The more is on the move, the more the system has to perform in real-time.
On the other hand, the server can be designed from the outset for the possible expansion of the fleet. Everything else poses no major challenges for the server applications. A few additional switches hardly burden the system. So-called infill stations, i.e., stations that are added later in the middle of the network, can also be implemented easily.
(Image:Â Andreas Sebayang/heise medien)
In principle, the operator can also choose their own servers and thus better consider their own interests, as long as the computers pass Siemens' initial health check. In general, however, Siemens assumes that servers will be ordered together and selected by Siemens itself. In Singapore, Signaling X was installed on HPE's Proliant servers of the 11th generation.
Singapore's Test Center and its Importance for Siemens
At the test center, the system for metro operation was initially only presented. As part of the presentation, there were various workshops for potential customers who could take a closer look at the system. Thanks to the test track, Siemens has ideal conditions for demonstrations here. In principle, Signaling X could also be installed at the Wegberg-Wildenrath test and validation center. But that is far away.
Consequently, several customers from the Asia-Pacific region traveled to attend. Of course, Singapore's metro line operators SBS Transit and SMRT are also examining the system very closely. Siemens is involved in all metro lines in the city-state with varying degrees of components. Sometimes it's the power supply, and in many cases, it's actually a CBTC installation with the highest degree of automation. The new Jurong Region Line will rely on Siemens' CBTC in 2029, but not yet on Signaling-X servers.
(Image:Â Andreas Sebayang/Privat)
Singapore is currently massively expanding its metro system at a very high speed. The Singapore Rail Test Center has a special significance here, as the city-state can now test vehicles and systems itself.
(Image:Â Bild: LTA/Government of Singapore)
Important acceptance runs will be carried out in the future on the three test tracks at SRTC: the outer ring (60 km/h, Endurance Track, 190 m radius), the inner ring (50 km/h, Performance and Integration Track, 140 m radius), and the high-speed track as a straight section (80 km/h).
Until now, this has mainly taken place in China, France, and Spain, as SBS Transit told us. Within certain limits, acceptance runs can be carried out on test tracks at depots. However, these are only about one kilometer long, not a circle, and complicate depot operations.
Currently, trains have to be transported to the test center by truck. However, there will soon be two rail connections to two metro lines. The first connection leads from the East-West end station Tuas Link to the test ring, which is quite adventurous by German standards.
(Image:Â Foto: Andreas Sebayang/Privat)
The Tuas Link connection leads into the center of the facility via the ring bridges over the water. Preparations for concrete supports are also visible everywhere on the test site, but were not allowed to be photographed.
(Image:Â Andreas Sebayang/Privat)
Developments in Germany
Formally, the Signaling X for Mass Transit system is intended for local public transport. In Germany, however, the distinction is somewhat difficult. Here, S-Bahn trains, such as those in Hanover or Cologne, belong to the main railway with partly its own infrastructure. However, the S-Bahn lines in Berlin and Hamburg mostly have their own networks, including special power supply. But even in Berlin (Birkenwerder) and Hamburg (Stade), they share tracks with the main railway.
On the other hand, U-Bahn (Berlin, Hamburg, Munich, Nuremberg) and Stadtbahn (Frankfurt am Main and many others) would be clear candidates for Signaling X for Mass Transit. In other countries, this is often classified as a metro system or light rail transit. However, the boundaries are fluid. In Germany, there are still few CBTC installations. Most are yet to come, and Siemens Mobility is often involved.
Frankfurt: Test runs from 2026
In Frankfurt am Main, for example, tram lines U4 and U5 will be equipped with CBTC. A workshop is already equipped for this. The first test runs in the network, but without passengers, are planned for this year, and the system is scheduled to go online in 2027. Further lines will follow by 2033. Operation without fixed signal blocks is planned. Instead, the signals move with a train in a "moving block" space distance, also called Moving Block.
At low speeds, trains can thus follow each other more closely, as the red signal moves in front of the train depending on the safety buffer for braking. Then, even in tight curves without visibility of the track (or signals), trains can follow more closely, which helps in reducing delays. In some systems, driving by sight is permitted for such situations. The Oslo Metro handles this particularly at Jernbarnetorget near Oslo Central Station. Incidentally, Siemens is also working on a CBTC installation in Oslo, and here too, initially without Signaling X. The first, three-kilometer section was commissioned last month.
Another project is underway in Hamburg. By the end of 2027, a line with seven stations between Jungfernstieg and Horner Rennbahn (U2/U4) is to be equipped. Like Frankfurt (M), the aim is to operate using a Moving Block system, thus reducing the headway from the current 150 seconds to 100 seconds in the future.
Berlin also plans to introduce CBTC on lines U5 and U8 by 2029 and 2033, respectively. The city already had an automatic research operation on the U4 in the 1980s but then abandoned the project.
However, these new projects only provide for Grade of Automation 2 (GoA2), i.e., only partially automated operation. Furthermore, the Digital Rail Germany project in the digital node Stuttgart relies on GoA level 2. In Germany, this is also referred to as "highly automated driving."
However, what sounds new is not necessarily so. The best-known example in Germany is likely the Nuremberg U-Bahn. It has been operating with a CBTC system according to GoA4 for a long time, i.e., completely without train personnel. The next GoA4 project will likely be the U5 U-Bahn line in Hamburg. stellwerke.info offers a good overview of CBTC projects in Germany: stellwerke.info.
High automation does not necessarily save personnel
Taking Singapore as an example, the small city-state already has a surprisingly high number of GoA4 systems today. And not just from Siemens, mind you. Alstom and Thales also play a major role here.
(Image:Â Strides/SMRT)
Operator SBS Transit is particularly impressed by the reliability. According to its own statements, the Downtown Line is one of the most reliable lines worldwide, ranking second behind a line in Hong Kong. The Mean Kilometers Between Failures (MKBF) is therefore 8,156,000 kilometers. The line is thus a kind of reference for Siemens, as both signaling technology, depot technology, and electrification come from the manufacturer, but also through the acquisition of Invensys in 2012, which initially equipped the Downtown Line.
Contrary to many assumptions, modern technology hardly saves personnel – at least in Southeast and East Asia. Every train has a Customer Service Officer. Those who travel on the Singapore Metro will usually find them at the front. According to SBS Transit, there is at least one Station Master and one Assistant Station Master at the stations. Larger stations also have more staff. In Germany, this would be a luxurious staffing level for stations, even though manual work is still common here.
Note: Siemens Mobility invited the author to visit the Singapore Rail Test Center and covered travel expenses.
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