The Great Western route modernisation is an extensive programme undertaken by Network Rail to electrify one of Britain’s oldest and busiest railways, providing greener, more reliable journeys. The focus of the programme is the Great Western main line (GWML), built more than 150 years ago.
For an investment of this scale, robust and timely rail asset data is essential for effective decision making but, with pressure for the survey to be completed in 12 months, traditional survey techniques were inadequate. Moreover, from a safety viewpoint, Network Rail wanted to minimise the work on or near the track and eliminate any disruption or loss of track availability to passenger and freight traffic.
To mitigate the time and safety issues, Fugro’s train-mounted rail infrastructure alignment acquisition system (RILA) provided the solution. Network Rail contracted Fugro to survey the primary routes in Western, Wales and Wessex regions, approximately 2,000 miles of rail track, using its RILA Track and RILA 360 systems.
The route requirements included the modernisation programme, the electrification scheme and the introduction of new high-speed electric trains for which Network Rail required a combination of topographical survey and six-foot and structure clearance analysis. RILA data, and some cleverly developed, complex algorithms, provided the gauging data for structures along the GWML and other alternative routes including relief lines, various loops and sidings.
What is RILA?
Traditionally, track measurements are undertaken by surveyors who work on and near the track and are exposed to the dangers of live railways whilst doing so. Conventional surveys are often restricted to night time working in short possession periods. Fugro’s innovative suite of train-borne RILA systems is able to measure the track and rail corridor in a fast and efficient manner, designed to keep trains moving safely, without interruption to services whilst keeping survey personnel away from the track.
The RILA Track system uses GPS, IMU (inertial navigation) and laser vision technologies. All equipment is installed in a transportable device that can be mounted to an automated coupler of a passenger train or to a set of buffers within just two minutes. Data acquisition is at line speed and, when installed on a regular passenger train, there is no need for additional train paths, limiting the disruption to train services.
The system is currently cleared to operate at 100 mph and at this speed will yield profiles at 10 cm intervals with an absolute accuracy of +/-10mm (plan) and +/-15 mm (height) without the need for ground control.
As the RILA Track system passes over the track, its laser vision system projects a laser beam over each rail with the integrated camera capturing high-resolution images of the rail profile and the coordinates of 1,400 laser points per railhead are calculated. The laser image of the rail head and rail foot provides high accuracy profiles and measurements (relative accuracy <0.3mm) that can be used to determine rail head and running edge wear as well as wear of S&C components.
The RILA Track system also incorporates an integrated video that can be georeferenced using the system’s survey data and used for desktop-based analysis and validation.
While the RILA Track system focuses on the track, the RILA 360 system incorporates twin 360° laser scanners and a panoramic imaging system to supply ultra-high density LiDAR point cloud data of the entire route. Each laser scanner rotates at 200Hz, recording one million points per second. Designed to be light and portable, the RILA 360 system connects to the back of a regular passenger train that has buffers in less than two minutes to enable it to scan the complete rail corridor, including track assets, structures, earthworks and vegetation. As with RILA Track, GPS, Active GPS reference network and IMU data are used to compute the absolute position of the point cloud.
The RILA systems work independently but they can also complement each other. The great advantage of deploying RILA Track and RILA 360 simultaneously is that four runs are undertaken with both systems, which supports the collection of high density, RILA 360 point clouds. Through an iterative process, and cross-referring adjacent tracks from each track’s own perspective, a homogenous point cloud and adjusted RILA track measurements are supplied to Network Rail Band 1A specifications. The result is an accurate, absolute XYZ model of all the objects in and around the track (including OLE componentry) and even higher relative accuracy of the objects, in respect of the track.
Speedy surveys and quality data
The entire survey was completed progressively on a phased approach throughout 2016. The entire section from London Paddington to Bristol was completed in only six shifts, immeasurably faster than conventional surveying with no requirement for track possession and no disruption to service.
One of the key requirements of the project was to satisfy Network Rail’s need for passing clearances. These ‘six-foot clearances’ were calculated at five-metre intervals from the measured track alignments, providing Network Rail’s project team with all the track distances in ClearRoute software format. This allows them to quickly analyse whether the new rolling stock will cause any infringements (early-warning data) and ensure that design parameters are adhered to.
Structure gauging files (SC0), which calculate the distances from structures (such as over- and underbridges and lineside furniture) to the tracks and their positions, are generated from the point cloud to analyse if all assets comply with the strict clearance profile. This is particularly important near platforms to check the gap between the train and platform for boarding (platform gauging or SCP files) and technical design (can trains pass this platform?).
The use of Fugro’s innovative RILA systems has given Network Rail access to a wide variety of asset management and track position data providing value for money while reducing the need for traditional surveys in open line working or track possessions.
“Our team has found the RILA and RILA 360 technologies to be safer, faster, more accurate and less expensive than any other method of acquiring datasets for sections of track longer than a mile,” commented Chris Flynn, IEP project manager at Network Rail.
RILA’s mantra is to ‘collect once and use many times’ and this was convincingly demonstrated on the section between Didcot Parkway and London Paddington, where the data have been used, not only for the previously detailed Great Western projects, but also for High Output Track Renewals and Crossrail.
This article was written by Rikkert Wienia, a project manager with Fugro
