MONITORING track quality across an entire railway network requires major organisation and substantial resources, and is vital to ensure the safety and reliability of passenger and freight services, not to mention ride comfort for passengers. Trying to reduce the cost of track quality monitoring across the network is an urgent challenge for all infrastructure managers as they work to achieve higher track maintenance performance.

To provide sufficiently reliable results, monitoring track quality often involves the expensive process of measuring track geometry. A less expensive, portable but equally dependable way of monitoring track quality is needed and dynamic measurement meets these requirements perfectly. Sensors can be installed on dedicated track recording vehicles or on any service train to assess track condition at any time on any section of the network.

This subject is at the heart of research on vehicle-track interaction today, and it is hoped that this innovative system could be implemented in current maintenance processes. Dynamic measurement sensors, such as accelerometers, can be easily fitted to passenger vehicles to provide a direct indicator of ride comfort or help to identify sections of track where the ride is poor.

As moving from measuring geometry to acceleration brings great challenges, it encouraged experts from around the world to launch the Harmotrack project in 2019 in collaboration with colleagues at the International Union of Railways (UIC). Today, over 300 experts from 64 companies and institutions in 40 countries around the world, including the US, Brazil, China and Australia, are contributing to Harmotrack. The main aims of the project are to:
• harmonise the application of acceleration measurement for track monitoring
• determine representative and dependable indicators of track quality based on acceleration measurements through data analysis of onboard and track measurements and/or multi-body simulation of vehicle-track iteration
• improve network safety and reduce maintenance costs by prioritising the correction of rail defects with the most dangerous impact on vehicle dynamics, and
• establish standardised acceleration thresholds in future international standards or technical recommendations.

The first phase of the project saw the establishment of the first global benchmark on the use of dynamic measurement to monitor track quality. This is an important milestone and enabled us to evaluate the current situation of this specific technology around the world, where it is being studied by many companies and research institutions. Three sub-working groups (SWG) were then created to tackle different technical challenges identified through benchmarking. Technical groups were created, and technical leaders were designated to coordinate the analysis and reporting phases. The SWGs began work in 2020, with technical research activities starting in parallel, and are structured as follows:
• SWG 1: determination of thresholds for acceleration
o SWG 1A: study of correlation between force and acceleration
o SWG 1B: study of correlation between acceleration and track geometry
- SWG 1B Alpha: assessment of optimal setup of filters
- SWG 1B Beta: study of correlation between acceleration and track geometry
o SWG 1B Beta 1: definition of acceleration thresholds using multi-body simulation of vehicles
o SWG 1B Beta 2: study of correlation between acceleration and track geometry using statistical analysis
~ SWG 1B Beta 2A: defect-oriented oriented analysis study
~ SWG 1B Beta 2B: study of the overall track analysis
o SWG 1B Beta 3: investigation of machine learning methodology
o SWG 1B Gamma: research on occurrence and risk analysis
• SWG 2: determination of the optimal use of axlebox accelerometers, and
• SWG 3: exploring the possibility of using low-cost portable devices (smartphones).

Harmotrack has created a huge international network embracing every continent, which is very dynamic thanks to the efforts of the Harmotrack management team and regular technical meetings. Two plenary meetings are held every year. The fifth was hosted by the University of Birmingham and British infrastructure manager Network Rail on June 13 and 14 2022, with 200 experts participating in person or online. Work is now underway to organise the sixth plenary meeting in June, which will be hosted in Rome by infrastructure manager Italian Rail Network (RFI).

This international collaboration has helped railways and infrastructure managers to create partnerships, while effective cooperation between the rail sector and research institutions as part of Harmotrack is making a positive contribution to bridging the gap between industry and academia. The Harmotrack non-disclosure agreement (NDA) signed by all 64 members has made it possible to share data, industrial practice and strategic information around the world in a truly ground-breaking way, providing the momentum for rapid technical work and forming the cornerstone of collaboration to date.

Unfortunately, processes and strategies for track maintenance and the use of dynamic measurement differ widely around the world, even within specific regions like Europe. By developing the detailed Harmotrack benchmark, we have been able to evaluate all these technical differences and identify potential solutions. Each company or country may have a different strategy for the use of dynamic measurement, but Harmotrack was able to build trust between experts and it is now easier to find common points of interest and identify technical solutions.

There are many different suppliers of dynamic measurement systems, but we decided to admit only railways, infrastructure managers and research institutions to work on technical topics and avoid any kind of commercial activity. The SWGs are focused entirely on technical topics and the trust established within Harmotrack facilitated the harmonisation of technical activities. The railways of some developing countries are official members of Harmotrack, which aims to help all countries to develop their own expertise and improve safety around the world with affordable railway technology.

International standard

We have now entered the final straight, working hard to reach the finishing line by the end of 2023. The SWGs are working to present their final technical results at the next plenary meeting in June, and will then collaborate on the final technical deliverable of the Harmotrack programme. They will be aiming to establish final guidelines to prepare the ground for drafting by the end of 2023 a UIC International Railway Solution (IRS) or voluntary international technical recommendations for the use of dynamic measurement for monitoring track quality.

To overcome the technical differences between different countries, railways and infrastructure managers, it is important to define minimal technical specifications that will produce satisfying results, as well as simplified but effective processes. The SWGs established a preliminary bibliography so that all members were on the same page before embarking on their technical tasks. The monthly meetings of the SWGs have enabled all participants to keep up to speed in terms of technical requirements.

We hope that IRS will lead to the harmonisation of current technical activities on the use of dynamic measurement and clarify the extent to which this technology can be used to monitor track quality. It will benefit suppliers who will be able to develop systems in accordance with minimal technical requirements, while infrastructure managers will be able to improve track quality monitoring by following specific, harmonised processes for the effective use of dynamic measurement. Research institutions will be able to use the IRS as the basis for further technical research.

The combined use of standard track geometry assessment and dynamic measurement will help to ensure that more regular track quality monitoring is undertaken using service trains or dedicated track recording vehicles. It should also reduce the cost of monitoring track quality, and improve the effectiveness of monitoring by combining measurements. At present, track geometry standards are based on the analysis of individual defects, but dynamic measurement enables the identification of dangerous combinations of defects that pose a risk to train safety.

In broader terms, adoption of the IRS should help to improve track maintenance, as dynamic measurement will assist with the transition from predictive to condition-based maintenance. It should also enable developing countries to adopt more cost-effective track monitoring technology to improve the safety of their railways.

*Danilo Sorrentino leads the Harmotrack project and is head of vehicle-track interaction at French infrastructure manager SNCF Network.