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Development of an Innovative Ground-Penetrating Radar System for Fast and Efficient Monitoring of Rail-Track Substructure Conditions

The continuous assessment of substructure conditions is a key need for rail-track maintenance activities. The SAFE-RAIL project tackles technological gaps that limit state-of-the-art systems by developing an innovative radar for fast and accurate monitoring of rail track substructure conditions.

Tags: Rail


The improvement of the European Transport Network is a key action for today’s sustainable development, and the revitalisation of railways is a priority that was envisaged in 2001 in the European Commission’s White Paper European Transport Policy for 2010: time to decide. In this context, the improvement of the capacity and safety of the railway infrastructure is strategic at both national and trans-national levels.

The accurate, fast and continuous assessment of rail-track surface and subsurface conditions has been recognised as a primary requirement of railway owners and users for minimising slowing traffic and optimising network capacity and safety.

Today, ground-penetrating radar (GPR) is the most promising technology for non-destructive subsurface investigation and buried object detection. Railway companies use GPR systems mounted on trains, lightweight carts or carried by hand in order to identify fouled ballast and trapped water on railroads.

However, the effectiveness of radar methods is now strongly limited by

  1. difficulties in estimating the ground dielectric properties with standard GPR antennas,
  2. inaccurate positioning of the collected data for systems on fast moving platforms,
  3. lack of onboard automatic data interpretation tools and anomaly detection capabilities,
  4. lack of an integrated IT approach in long-term monitoring of large (trans-national) railway infrastructures.


The SAFE-RAIL project was designed and proposed for developing efficient technological tools for continuous assessment of hidden and hard-to-monitor substructure conditions in a fast and accurate way. These tools will allow increasing risk-management and accident-prevention capabilities while optimising the planning of construction, reconstruction and maintenance operations along the rail network with minimum degradation of rail network capacity.

Though radar technology is used today for underground analyses at rail-tracks in conjunction with well-established methods for surface inspection, a consistent technology gap is still present, preventing the full exploitation of the radar’s potentials on high-speed automatic rail diagnostic and monitoring systems, as well as during railroad construction works.

The SAFE-RAIL system is based on a completely new concept of rail-track substructure monitoring radar and on innovative data interpretation and analysis tools, based on expert systems and neural networks providing field information in a user-friendly way. This will allow full integration of the SAFERAIL subsurface monitoring system on high-speed diagnostic trains for

  1. real-time subsurface assessment and delivery of ‘diagnostic’ information to the onboard operator, and
  2. storage of the collected information for long-term multi-temporal analyses.

The SAFERAIL on-board processing system
The SAFERAIL on-board processing system

Description of work

Based on an evolutionary approach specifically intended to overcome the identified limitation of conventional radar instrumentation, the SAFE-RAIL project has developed an innovative rail-track substructure condition monitoring system, consisting of:

  • the new fast substructure radar (FSAR), based on innovative antennas, which allow precise estimation of layers’ and buried objects’ dielectric properties while maximising penetration depth under any terrain conditions, the accurate estimation of wave velocity in the sub-ground, an effective clutter cancellation, and high-speed platform operations
  • the high-performance radar control unit (HPRCU), that allows real-time control of multiple channels and recording of raw collected data supporting train speeds higher than 300 km/h
  • an innovative rail-track positioning unit (RTPU), allowing fast and accurate measurement of the platform position and radar triggering
  • an innovative onboard processor (OBP), based on expert systems and neural network algorithms for real-time raw GPR data interpretation and user-friendly presentation
  • a networked data interpretation and processing software (N-DIPS) supporting long-term monitoring of rail substructure conditions through the networking of different sensors operating along multiple segments of the railway infrastructure.


D’Appolonia is coordinating an expert team of scientists, technologists and geophysicists from different European industrial companies, service providers and research institutes.

Promising results have been obtained with the first SAFERAIL prototype, which has been recently exercised on rail-track test sites. Integration on the MER MEC test-train is in progress, and the 2007 campaign of acquisitions on the European Rail Network will provide the final assessment of the SAFERAIL capabilities and performance.

The successful completion of the SAFE-RAIL project will lead to:

  1. demonstrating the capabilities of quickly and accurately referenced detection and classification of rail-track condition deterioration in the rail-track ballast, sub-ballast and sub-grade
  2. providing a prototypic processor for user-friendly onboard diagnostic data interpretation and early warning against the probability of critical failures of the rail network.

The full exploitation of the SAFE-RAIL scientific and technological results will lead, in the mid-term, to the provision of improved performance diagnostic systems and platforms, including powerful radar-based subsurface assessment capabilities. These will allow more efficient, cost-effective, faster and safer construction and re-construction of railroads, as well as optimised planning of railway network maintenance strategies.