Optimising the rail track system

Existing track systems (namely ballast tracks in Europe) struggle to keep up with ongoing increases in operational traffic, demand for reliability and lifecycle cost (LCC), and the need to decrease noise and vibrations. This is exacerbated by the fact that the adoption of innovative new track solutions is often slow due to the need for extensive testing and acceptance procedures.

As a result, maintenance costs for track components remains around 50-60% of a railway infrastructure’s total maintenance costs. Track-related installation costs also account for a significant portion of total installation costs, while direct, secondary, and long-term costs related to malfunctioning track structures are massive. Furthermore, fixing these issues often involves large track works, which can shut down traffic for a considerable amount of time.

Clearly what is needed are improved track system solutions that require less maintenance and offer improved precision in identifying exact maintenance targets and better installation methods. Helping to answer this need is the Europe’s Rail Joint Undertaking (JU). Through various technical demonstrators (TD), the JU aims to deliver innovative technologies and components for premium track structures.

Switch and crossings

One such component is switch and crossings (S&C). The basic design of S&C assemblies has remained unchanged since their inception. As a result, S&C related failures account for an estimated 25-30% of all infrastructure failures on some European railways.

Add to this the significant proportion of the S&C LCC relating to the monitoring and maintenance activities needed to ensure that the system is functional for the safe running of trains, and it’s easy to see why critical S&C failures must be substantially reduced.

To do this, the JU proposed two TDs:

• Enhanced S&C system demonstrator
• Next generation S&C system demonstrator

Enhanced switch & crossing system demonstrator

Objective

The main objective of the TD is to improve the operational performance of existing S&C designs, delivering new S&C subsystems with enhanced Reliability, Availability, Maintainability and Safety (RAMS), LCC, sensing and monitoring capabilities, self-adjustment, noise and vibration performance, interoperability, and modularity.

The research

The research involved developing enhanced S&C whole system behaviour models that could be used to better understand the system and to optimise its design. It also utilised computer aided engineering (CAE) as a means of integrating mechanical, electrical, and software components into the design.

One of the key outcomes of the research was the development of improved components and technologies capable of optimising the points operating system (actuation, locking, and detection) for RAMS while also reducing whole system LCC. Another key outcome of this work was the development of new sustainable materials to minimise deterioration and failures, extend asset life, and reduce maintenance needs.

The research also looked to enhance the wheel-rail interaction’s impact on the durability of such key components as switch parts/blades and crossing nose. In addition, it looked at developing enhanced inspection, monitoring, and measuring systems based on the use of embedded and integrated sensors that would enable self-diagnosis and the remote condition monitoring of an asset’s condition, deterioration, and performance.

Outcomes and key results

Based on the aforementioned research, several demonstrators were developed:

• Laser cladding of components and the use of heat treatment as a viable maintenance procedure were demonstrated
• Demonstration of some aspects of using integrated and embedded sensors for prognostic monitoring, the integration and deployment of data acquisition and transfer methods, as well as the in-bearer sensor technology for crossings to remotely assess the condition of a crossing profile and the impact force in the wheel transfer area.
• An in-hand laser scanning device for assessing the wheel contact point on a switch rail and to check for potential derailment hazards was developed.
• A condition monitoring procedure was developed to monitor and predict S&C conditions. The procedure estimates the degradation status of the crossing panel by combining simulation models with data from the sensors embedded in the S&C structure.
• A S&C virtual model configuration was developed to simulate the dynamic behaviour and related deterioration of components caused by the interaction with passing vehicles, with the goal of advancing the use of virtual authorisation.
• The development of a new whole system modelling (WSM) sub-model for crossing nose rail material behaviour and its impact on wear and rolling contact fatigue in turnouts was partially achieved.
• A demonstrator of an optimised cast manganese frog was developed and used to evaluate the performance of a bainite to manganese steel weld.

A full-scale switch and crossing demonstrator was tested in an operational environment under realistic dynamic loading conditions. Additional system monitoring, going above and beyond the designed system remote condition monitoring, have been developed and used to provide performance data that can be compared against existing S&C systems.

Other outcomes and findings of note from the demonstration activities include:

• Demonstrator of the joint welding of bainite steel components achieved good results, although recommended fatigue test must be completed.
• Three different cast manganese frogs have been optimised, with fatigue model testing and in-track monitoring providing very promising results.
• Demonstrator for the prognosis of ballast degradation and S&C wear behaviour was conducted on a turnout site equipped with pads, with promising results. However, a full analysis of reduced ballast degradation has not been completed.

Conclusions

By developing a truly cross-functional and integrated S&C operating system that uses modern technology in innovative ways, the research opens the door to new opportunities for infrastructure managers. Leveraging this work, they are in a position to provide real-time preventative maintenance activities that will increase system longevity and availability and, in doing so, increase service revenue while reducing the need for manual intervention.

Next generation S&C system demonstrator

Objective

The main objective of the TD was to provide radical new S&C system solutions. By embracing new designs that use completely new methods for switching trains between tracks, these S&C system solutions aim to drastically improve capacity and performance and reduce costs – all while maintaining safety as an overriding factor.

Discussion

Not constrained by traditional S&C setups, the new designs focused on using advanced materials, enhanced elastomeric components, optimised sensor technologies, and adaptive controls with active control closed loop feedback for self-adjusting/compensation.

The TD also explored the potential of applying nano technology to metallurgy, with a particular focus on self-healing properties, as well as the use of composite and other non-ferrous combinations. Furthermore, friction modifiers and lubrication systems were investigated as a way of coping with new technologies and harsh environmental conditions (e.g. sand, ice).

Overview of work performed

Conventional S&C design incorporating many next generation concepts

This demonstrator was used to assess the individual and collective improvement potential for each next generation technological development. The subsystems were meant to contribute to a future WSM, ultimately demonstrating the benefits of making incremental changes to existing S&C design. It also looked to contribute to an improved system RAMS by designing out known failures.

The benefit of this approach is that it allows multiple long-term technologies (as opposed to fewer, short-term incremental improvements) to be introduced to the existing S&C system. Unfortunately, the demonstrator delivered little, incomplete, or undocumented progress.

A series of individual demonstrators

This task was meant to carry out the necessary tests to determine the functional performance of the subsystem assemblies. Work included kinematic system design and progressing the design to the production of a prototype of the next generation points operating equipment (ALD).

The work supported the manufacturing and assembly of first-of-type components and subsystems to enable the necessary testing for design validation. This also ensured the continued embedment of advanced switch controls to be installed on a future integrated next generation S&C system demonstrator. Furthermore, the work partially identified the information needed to interface the S&C to a remote interlocking via, for example, a networking protocol.

Another important aspect of the task was the design of the components and development of the prototype, including the manufacturing and testing of the S&C system’s individual components and materials. Various manufacturing processes, such as additive manufacturing, were also explored as a means of optimising and scaling the manufacturing process towards mass production.

Next generation S&C concept

The main feature of this S&C concept design was its lack of conventional switch rails and crossings, a feature made possible by integrating component and subsystem developments into a holistic, whole-system virtual demonstration.

Although such an approach would enable a small-scale physical component demonstrator to be developed and tested in a lab, this did not happen due to issues with the supplier. If such a demonstrator was developed, it would have included a novel wheel rail transfer design that eliminates the need for moveable switch rails.

That being said, a demonstrator for the innovative tramway moveable point crossings was successfully tested and, following virtual and prototype development, progressed into a physical demonstrator.

New automated inspection and repair technology

The aim of this line of work was to reduce the need for on-track human activities and to improve worker safety by limiting their exposure to site-based hazards. To do this, the task aimed to deliver automated and accurate inspection of the next generation S&C system. This was to be done using remote controlled vehicle-mounted technology and drones. Unfortunately, limited success was achieved, and the research was not completed.

The task did find success in its use of autonomous repair technologies for repairing isolated rail defects. The work reached TRL 5/6 (technology validated/demonstrated in relevant environment) and was demonstrated on current S&C designs with a combination of milling and welding processes under computer numerical control. However, the repair of discrete rail head defects has not yet been fully demonstrated. This technology is applicable to the automated restoration of worn/damaged crossings and is ready to be further developed into feasible concepts for demonstration within an industrial relevant environment.

Conclusions

The TD set out to develop demos (up to TRL 5/6) capable of demonstrating the performance of new component and subsystem designs and, where feasible, integrating them into a whole-system prototype. This was to be done primarily using traditional switch rail and crossing configurations as a basis for incorporating other step-change subsystem and component developments, with the end goal being achieving the required next generation S&C whole-system performance.

The TD also set out to develop a radical next generation S&C whole-system virtual demonstrator (up to TRL 4 – technology validated in lab). The virtual demonstrator was to integrate future system capabilities into a holistic design concept.

Other track system technologies and components

Beyond S&C, the JU also looked at ways to optimise and improve the overall track system. It did this primarily through two TDs:

• Optimised track system
• Next generation track system

Optimised track system technical demonstrator

Objective

With the goal of improving the operational performance of existing track systems, the optimised track system TD aimed to fundamentally challenge track construction assumptions that are implicit in current European track design.

The TD explored how new construction designs can make use of modern materials to provide high levels of sustainability, capacity, and LLC savings relative to existing construction types. In addition to investigating innovative products, processes, procedures, and construction methods, the TD also looked at ways to renew existing track assets.

 

Optimised track system TD goals

• • Increase track lifetime.
  • Decrease traffic disturbances caused by track maintenance and faults.
  • Provide tools that infrastructure managers can use to find track solutions that are technically, economically, environmentally, and operationally beneficial.
  • Develop a comprehensive set of tools that enable the proactive management and maintenance of track systems.

 

Discussion

At the core of the TD was a desire to provide an opportunity for the large-scale validation of innovative solutions and the quantification of their benefits. To ensure that all solutions meet actual user needs, the TD worked closely with infrastructure managers and all solutions were developed and verified with vehicle interaction in mind.

Based on this cooperation, a number of demonstrators were developed.

Innovative track solutions, along with prototypes for innovative track condition monitoring and track maintenance, were developed to different levels of maturity, with the most promising solutions being validated via testing and demonstrators.

The demonstrators focused on the future requirements for track systems and incorporated expectations on future operational loads, maintenance possibilities, LCC and RAMS levels, climate impact, etc. The intention was to show how the proposed track system solutions would impact high speed/mainline, regional, freight, and urban/suburban traffic conditions.

The idea behind the demonstrators was to validate optimum combinations of technology innovations and demonstrate the expected benefits of the innovations through identified KPIs. They also aimed to ensure the safety, interoperability, and competitiveness of rail by selecting those solutions that could best meet such challenges as capacity/user demand, reliability/quality of services, and LCC/competitiveness.

Outcomes and key findings

The TD produced demonstrators that aimed to:

• Reduce overall LCC and enhance RAMS
• Increase track performance and decrease traffic disturbance
• Improve environmental performance
• Decrease the occurrence/magnitude of wear and RCF on rail
• Increase track geometry performance
• Improve track stiffness (including reducing stiffness deviations)
• Decrease noise and vibration
• Improve the monitoring and validation procedures used to enhance control over deterioration.

The delivered demonstrators can be grouped into the following areas:

Overall new track systems

• Innovative slab track system called 3MB. Monitoring and analysis of the system in operation was completed, performing an extensive in field inspection and proposing improvements and further opportunities for optimisation. (TRL 6 – technology demonstrated in relevant environment).
• Development of a transition design/specification between slab track and conventional ballasted track form. The demonstrator improved track performance in terms of dynamic response and included the application of ballast glue and a comparative evaluation phase of long-term performance. (TRL 7 – system prototype demonstration in operational environment).

Rails

• Optimised rail damage prevention and mitigation strategies for combating different types of rail damage. Influencing parameters and predictive models were developed, as was a means of reducing deterioration by altering operational conditions.
• Methods for measuring stresses, RCF, geometry degradation, stiffness, friction, and material defects were investigated, with the aim of facilitating high precision asset management.
• Research on ways to advance such deterioration prevention techniques as friction management, grinding/milling, and rail grade optimisation.
• Studied damage mechanisms on bainitic steel and performed microstructure investigation of the base material and heat affected zones. Based on this work, proposals were made to modify the previously used bainitic grades to optimise rail and weld properties.

Optimised wheel/rail interaction

• The demonstrator started by investigating how optimised wheel/rail interaction could improve safety and comfort, decrease noise, and improve overall performance.
• Research included looking at how vehicle stability performance was impacted by wheel/rail interaction. This allowed for the determination of a stable and robust shape of a wheel/rail profile in terms of stability of the ride (TRL 7).
• The demonstrator also evaluated the influence of out-of-round wheels on the probability of rail breaks (under different operational conditions), along with the feasibility of further restricted operations.
• The performance requirements of the friction modifier were assessed, and the impact of laser clad and heat-treated rails (in perspective of the wheel/rail interface) were determined.

Sleeper and other rail support solutions

• Explored the use of new materials (re-use, recycled) in the design of rail support solutions as a means of increasing sustainability and improving performance.
• A new composite sleeper made mainly from high-density polyurethane and hemp fibre was developed as an alternative to timbre sleepers.
• New solution designs for reducing loads and increasing durability and track stability were proposed. This includes integrating elastomeric elements as a means of mitigating vibration, decreasing variations in track stiffness, and increasing ballast life expectancy.
• Developed new designs that account for altered operational demands. This includes a design to minimise the effect of the flying ballast, which is becoming a growing problem on high-speed lines.

Noise and vibration

The demonstrators related to noise and vibration focused on solutions to:

• Prevent high-frequency range vibrations at the source.
• Dampen or intercept the dispersion path within the track structure.
• Passively dampen, reflect, or shield the radiation of noise and/or vibrations.
• Identify methods for jointly assessing both noise and vibrations.
• Use under sleep pads and under ballast mats to reduce noise and vibration emissions.

All solutions were evaluated via slab track operations using numerical assessment and validations.

The demonstrators also investigated methods to predict and mitigate curve squeal from curves with small radii and ways to reduce noise after the machining of rails.

The outcome was a library of performances for different track solutions, with mitigating vibration levels expressed in 1/3 octave bands and with a preferable maximum frequency of up to 1 kHz.

Integrated maintenance procedures

The demonstrators related to integrated maintenance procedures focused on optimising:

• Condition monitoring
• Tamping
• Grinding and milling
• Lubrication and friction management
• Intelligent repair of track components

The demonstrations included the development of embedded sensors in the track system, enhancing maintenance decisions and resulting in improved prognostic and health management. The sensor is designed to measure temperature, vibration, and noise. Eventually, the use of AI will allow the data to be processed and used to predict failures.

The work also demonstrated how enhancing tamping parameters, in combination with a georeferenced track geometry measurement system, can improve the performance and efficiency of the ballast tamping processes.

Conclusions

Together, the demonstrated new track and maintenance technologies will contribute to an estimated 20-30% increase in capacity. This is the result of their ability to deliver decreased track disturbances, less invasive inspections and maintenance interventions, reduced track failures and deterioration, and reduced noise and vibrations.

The demonstrators also achieved a 10-20% reduction in LCC for some track systems, particularly for the developed innovative slab track. This is due to the solutions’ modularity, which reduces installation and replacement costs, extends the use of recyclable materials, and enables the development of new cost-efficient solutions using virtual testing.

Last but not least, the developed solutions have the potential to increase reliability (and punctuality) by 20-30%, the result of their ability to reduce unplanned maintenance and operational disturbances.

That being said, there is room for improvement, with further research and development likely to bring larger and more tangible benefits.

Next generation track system technical demonstrator

Objective

Like the optimised track system TD, the next generation track system TD identified and evaluated innovative track solutions. However, unlike the optimised track system TD, the solutions developed in this TD have a targeted horizon of around 40 years beyond the current state-of-the-art.

Thus, instead of prioritising harmonisation with today’s railway system, this TD prioritised step changes in performance. This allowed the TD to focus on providing key railway functionality without being restricted to current practices.

 

Next generation track system TD goals

• • Increase track lifespan.
  • Decrease traffic disturbance due to track maintenance and faults.
  • Provide tools that infrastructure managers can use to find track solutions that are technically, economically, environmentally, and operationally beneficial.
  • Develop a comprehensive set of tools that enable the proactive management and maintenance of track systems.

 

Outcomes and key findings

At the core of the TD was a desire to develop new innovative technologies for premium track structures that can increase profits and lower customer costs. To ensure that all solutions meet actual user needs, the TD worked closely with infrastructure managers and all solutions were developed and verified with vehicle interaction in mind.

Based on this cooperation, demonstrators with the highest potential for delivering the necessary step change in track performance were delivered. These demos cover both next generation track system design and next generation track maintenance.

Next generation track system design demonstrators

• Integrated method for assessing vibrations induced by railway traffic and the potential impact this has on nearby receptors.
• Improved method for assessing critical speed for slab track solutions applied in soft soils and based on advanced numerical modelling.
• Investigated different grout materials’ potential for providing better interaction and durability when supporting precast slab track units.
• Ad-hoc reinforced cement-based mortars that facilitate the debonding process whenever the replacement of one or several track modules is needed (tested to TRL 5).
• Use of innovative and smart materials using fibre-based sensors (self-sensing cementitious geo-composites) for continuous monitoring and damage identification and localisation. Two approaches were tested where the piezoresistive effect can be provided, one randomly using conductive and another by directionally oriented fibrous materials. Both approaches proved capable of partially enhancing cement-based geo-composite self-sensing capabilities when applied to smart rail track structures (TRL 5).

Next generation track maintenance demonstrators

The next generation track maintenance demonstrators focused on developing technologies and processes up to TRL 6 that can be used for the early identification or prediction of component and system failures. Embedded sensing and monitoring requirements, together with autonomous inspection and repair techniques, were developed to improve efficiency and reduce the need to conduct these tasks on site, thus improving the safety and well-being of staff.

• A non-destructive method for measuring thermal rail stress and facilitating calibration-free measurement of longitudinal stress with mathematical models to directly predict the stress (TRL 6/7).
• Measurements of the dynamic responses of tracks to passing trains as a means of better understanding and monitoring the rate of change of track stiffness over time (TRL 4/5).
• An autonomous rail defect inspection system used to demonstrate the accurate, autonomous, and ongoing identification and reporting of rail head defects (TRL 6/7).
• Work on the rail repair by cold spray additive manufacturing concept.
• A demonstrator of an embedded monitoring and sensing system with the objective of providing real-time data to enable efficient monitoring, defect prediction, and general track system management was started but not completed.
• An instrumented demonstrator (TRL 6/7) based on vehicle borne monitoring and autonomous inspection of plain line applications, including non-contact systems for detecting rail defects. The demonstrator allowed for the continuous on track measurement (at low speed) needed to identify the constraints and adaptations for enhancing the measurement system in real conditions. The prototypes embedded into the demonstrator aimed to develop and demonstrate the use of a contactless, ultrasonic, EMAT-based method for identifying rail-level defects.
• Demonstrator of the prototyped non-destructive method of measuring thermal rail stress.
• Smart integrated system demonstrator for transition zones. The demonstrator should have included a physically integrated self-sensing material capable of providing data to the transition zone dynamic models. While the work to develop the demonstrator included the initial design and specification of the whole system, including materials and prediction and information models, its installation, calibration, and validation in an operational environment were not achieved. Thus, the demonstrator only achieved TRL 5/6.
• The partial demonstration of automated/autonomous repair technology capable of providing high-quality and repeatable repair interventions with minimum human support.

Conclusions and next steps

The TD’s aim was to identify and evaluate next generation innovative track solutions with a targeted time horizon of around 40 years beyond the current state-of-the-art. This means that some of the solutions researched and achieved are still too innovative for their benefits to be fully quantified.

That being said, many of the solutions developed within the TD will contribute to reducing track system installation costs and to ensuring the longer durability and stability of those track sections with traditionally higher maintenance requirements.

Take for example the automated/autonomous repair technology prototype, which demonstrated an automated solution for discrete repair of rail defects. This technology, together with the automated inspection recording vehicle, will likely deliver significant improvements in the rail repair process, both in terms of cost and risk reduction and regarding the impact these repairs have on capacity.

There’s also the prototyped non-destructive method for measuring thermal rail stress, which will enable the early detection of defects that could have catastrophic effects on operational safety.

It is also worth noting the array of benefits expected from the development of an instrumented vehicle for the autonomous monitoring and inspection of plain line applications. Although not fully quantifiable at this early stage, it is safe to say that the potential benefits will be significant. The same can be said of the rail repair by cold spray additive manufacturing concept. Even if it did not reach the expected level of maturity, it did demonstrate its potential for delivering significant benefits in terms of rail repair.

Both solutions, along with many others that were started during the TD, are clearly worth continuing in order to make them widely viable, commercially applicable, safety approved, and, eventually, adopted by the industry.

The following innovations in particular are ripe for further investigation and prototyping as they all have the potential to deliver significant benefits in terms of reducing LCC and maintenance and increasing system reliability:

• Transition slab self-monitoring/sensing systems
• Cold spray additive manufacturing
• Non-destructive method of measuring thermal rail stress
• Comprehensive digital twin adding the full new module allowing referencing RCF defects to be used in statistical analysis and in predictive maintenance