A well-honed rail network allows punctual train operations, stimulates trade and supports the goal of decarbonising passenger and freight transport. To increase network capacity and at the same time encourage modal shift to rail, DB InfraGo is pursuing several approaches. One is the strategic expansion of the network by building new lines or reopening those closed in previous decades. Another is maintaining and enhancing the capability of existing lines. This is currently being achieved through comprehensive line renewals, with major engineering work scheduled to take place over several years.

Effective maintenance of existing lines is key to delivering German Rail’s (DB) high-performance network. Today, around 3500km of the German rail network is considered to be heavily used, mostly by a mixture of freight and passenger traffic. Even before engineering work is taken into consideration, these stretches of the network have an average capacity utilisation of around 125%.

As passenger and freight traffic volumes are expected to increase in the coming years, the size of the German high-capacity network will almost triple to over 9200 km by 2030. Infrastructure manager DB InfraGo’s capacity management planning aims to reduce the number of delays to trains running on the network while achieving a more uniform timetable under the Deustchland Takt regular-interval timetable project. Furthermore, the aim is to ensure that the corridors are free of construction work for several years to reduce the number of track possession hours.

One of the ways DB InfraGo is improving resilience of the high-capacity network is demonstrated by its partnership with Vossloh to deliver preventive rail maintenance. Since 2023 both parties have been implementing high-speed grinding (HSG) technology to help counter the effects on the rail head of increasing loads over the most heavily-used sections of the network. The HSG system developed by Vossloh is the only rail maintenance process in the world that can be deployed without disrupting train operations.

Vossloh originally developed its HSG technology around 20 years ago in response to the following issues:

• increasing wheelset loads and train speeds on high-speed lines increasingly led to the rail surface becoming brittle
• the rate of formation of rail defects was outpacing corrective machining and the planning lead time for treating rail defects was taking too long due to high network use, and
• customers requiring the maximum rail life rather than short-term repairs.

The aim was to prevent cracks in the rail head and thereby extend the service life of the rails. Smoothing the top of the rail by removing defects also reduces noise at the wheel-rail interface.

Since 2011 the HSG train has been approved for the maintenance of certain parts of the national network where it provides an economical alternative to acoustic rail grinding to reduce operational noise using grinding stones.

Thanks to an elongated contact line, the grinding wheels remove brittle surfaces (hardened surface layers) as well as the early formation of corrugation from the rail. Since HSG does not continuously touch any part of the rail head there is no risk of the rail overheating. With an achieved surface finish of between Ra 4-8µm, HSG is a very efficient process for noise reduction. A low surface finish also serves to prevent serial squats, as recent research has shown. A finish of less than 4 µm can also be achieved by making further passes with fine abrasive media.

Measurement and grinding

DB InfraGo’s maintenance strategy for the entire high-performance network specifies three grinding campaigns per year at four-month intervals. While work was initially carried out with a homogeneous removal rate of 0.1mm each time, since May 2023 it has been carried out according to the requirements of individual stretches of track based on recorded measurements. DB InfraGo has also commissioned the use of extensive digital measurement and analysis technology to provide even greater accuracy.

The smart HSG train has integrated measurement technology to carry out transverse and longitudinal profile measurements and is also equipped with a trolley for eddy-current testing for even more reliable crack detection. The sensor technology works relatively autonomously and measures both rails simultaneously, making it possible to also determine the track gauge. The wear reserve in the rail head can also be measured by means of transverse profile measurement. All condition data is recorded to the nearest metre and location checked. When measurement begins, the odometer starts via the rotation sensor. Global navigation satellite systems (GNSS) also support accurate location determination. As rail diagnostics always take place in the direction of travel, the measurement data can be clearly assigned to the corresponding track.

With each measurement run, even while grinding is taking place, rail condition data is transmitted to a secure, centralised database in the cloud, where it is available for algorithm-based processing. The data can be used to provide baseline information for each line and can also be fed to the Maintenance Planning Made Easy (Mapl-e) app, which can be installed on any compatible end device. This integrated data collection and software solution provides the enormous advantage that the data collected by sensors on the smart HSG train is pre-processed before it reaches the app and is therefore immediately available to the end user (see image).

Mapl-e offers users the ability to check and compare possible maintenance scenarios.

Unlike other solutions, Mapl-e is not limited to displaying measurement data in different levels of detail, but additionally divides the measured track into sections, depending on the type and depth of defect, and visualises the rail condition intuitively using traffic light colours, red, yellow and green. This simplified assessment of good, bad and critical condition can be quickly and easily adjusted at any time by changing the threshold values and their effects on shift performance and costs can be seen. Thanks to this overview function, line sections requiring further work can be prioritised and appropriate repairs can be planned in a targeted manner. In this way, Mapl-e simplifies the entire planning and control process for rail maintenance.

Based on the insights gained from Mapl-e, and thanks to the new HSG grinding unit, the sensor data is used to automatically select the grinding profile during the subsequent grinding campaign with the help of the grinding profile generator. This procedure offers both a targeted response to the detected condition of the rail cross-section and precise guidance of the grinding discs along the running edge. In the following grinding cycle, the grinding wheels can be moved from the running surface to the running edge if necessary.

The running gear of smart HSG units can be elastically spread for guidance so that the wheel flanges are in contact with the rail. Without additional sensors or electronics, the running gear guides the abrasive wheels through sections in which the track widens or narrows. When traversing curves, the unit running gear (and therefore also the grinding discs) follow the track so that the entire grinding unit can align itself independently of the base vehicle. When travelling through points, a system of track guides prevents wheels from running through the frog gap onto the diverging track. The guides run along with the wheels and pull them away when approaching frog gaps. This allows the grinding units to safely negotiate points at full working speed. Pressing the grinding discs against the rail relieves the load on the grinding unit running gear, which could potentially lead to derailments. The grinding wheels are pressed against the base vehicle using a hydraulic system which is also used to lift the grinding units into the transport position.

Digital rail maintenance

Moving from interval-based to condition-based maintenance gives infrastructure managers increased flexibility. The common goal is an improvement in rail quality, which is achieved through the intelligent evaluation of measurement data and maintenance measures tailored precisely to the needs of the track. At the same time, less corrective rail maintenance measures are required, which equates to fewer track possessions. All this leads to lower costs and higher line availability. Mapl-e is highly customisable to allow customers to specify their own operating and network parameters and maintenance preferences.

With smart HSG, we are moving away from the cyclical maintenance approach with its homogeneous removal of rail. Regular measurement campaigns over time build up an accurate and holistic defect history in order to predict defects and act to avoid them at an early stage. The ability to predict how the rail head cross-section will change increases with each measurement. With a sufficient database and using the Mapl-e app, the rail condition can be simulated and grinding cycles adapted or alternative rail processing methods planned in good time. Using AI-supported algorithms, the web app evaluates different maintenance options at the touch of a button, providing plant managers with a recommendation for the most suitable rail processing vehicle. The processing times and costs for these vehicles are also calculated.

HSG enables targeted, minimally-invasive measures to be carried out, significantly boosting network capacity. At the same time, the use of digital technology paves the way for predictive rail maintenance. Further development of the grinding train into a diagnostic vehicle has several pioneering advantages: for the first time, it will be possible to collect data on rail condition at speeds of up to 120km/h without closing the line or disrupting services. At the same time, rail maintenance and condition diagnosis are efficiently combined in just one pass. This move away from total line closures for engineering possessions means that infrastructure managers can generate additional track access charge income with fewer restrictions on network use.

To achieve a minimum coverage of 13,000km year, Vossloh organises and coordinates all tasks associated with the grinding campaigns, including planning where and when grinding is to take place, booking train paths and responding dynamically in the event of disruption. Infrastructure managers aim to maintain high availability across large parts of the high-capacity network when scheduling grinding campaigns.