I remember my early days as a railway engineer, when it was our job to carry out a detailed site survey in preparation for a track renewal. I also remember the words of wisdom offered to me by the senior technician in charge at the time. He said to me: “You just need to make sure that you get the survey right, and the rest will just follow on.”

So, armed with these wise words hewn from years of experience, and supported by the very capable assistance of the local survey gang, we proceeded to walk through the site to be relayed, checking for any overhead obstructions, over and under bridges and so on.

This was followed by a more detailed survey with regular ‘six-foot’ measurements taken from the adjacent line then offsets were measured from a constant chord length throughout the curved and transitional elements of the layout, carefully recording all the detail in our survey book. This work was carried out whilst trains were passing at line speed, the protection being a lookout man with another lookout in advance.

Preparing the Hallade scheme

Back in the van, the Sudoku-literate engineer would be developing a Hallade survey based on the measurements that we had collected. The scheme would be designed to accommodate the new proposed line speeds following the renewal.

The best bit then followed – driving wooden pegs into the cess ballast at set distances, a very therapeutic pastime, before tapping nails into the pegs offering a final and accurate offset designed for the new layout.

As you would expect, there was always a constant banter, often focused on how this process could be made more efficient – laser technology for example, was beginning to emerge as a possibility. However, we knew that driving in wooden pegs and dodging trains was going to be the norm for some time.

I am pretty sure that the thought of a drone fulfilling all these requirements would have been quickly dismissed as fantasy, more suited to an Isaac Asimov novel than the realities of track renewal.

Well, science fiction is becoming reality and the first track renewal with a detailed survey developed using drone technology will be undertaken in the next few months at Salfords, located on Network Rail’s South East Route in Sussex. The site is approximately 500 metres long and includes four main line tracks, three S&C units and two sidings.

Rail Engineer spoke to Adam Littlewood, who is the Network Rail Infrastructure Projects (IP) track development programme manager responsible for this work, along with Michael Alldis, the project manager accountable for ensuring that the chosen technology achieves the challenging project schedule and delivers the requirements specified.

Vogel R3D UAV

To help Adam and Michael achieve this objective, Network Rail has procured the services of Plowman Craven, a firm of chartered surveyors based in Harpenden, Hertfordshire. It operates worldwide, having developed a full range of measurement services to a long list of customers, and one of the newest of these services is wrapped round its Vogel R3D, which is a unique Unmanned Aerial Vehicle (UAV) – a ‘drone’ to you and me!

So why is it that this piece of technology is now catching the eye of those involved in track renewal?

One of the reasons is that the Thameslink project is planned for completion by the end of this year, and Network Rail has been developing a resilience programme of work, identifying locations where the infrastructure needs attention to ensure that the new route is robust and ready to receive the new Thameslink rail service. A £50 million package of accelerated track renewal work has been identified, and Salfords is one of a number of projects commissioned for this resilient programme for delivery by IP Track.

Also, like many of the projects identified, the site at Salfords is one where it is difficult to get possession to enable a survey to be carried out safely. When a possession is offered, the time allowed is usually very limited and the cost of ensuring that the work is carried out safely becomes significant. This is what encouraged Michael to start looking at alternative approaches and why the Vogel R3D UAV drone started to look like a very attractive option.

Control points

The work on site can be carried out by just three skilled operatives without needing to take a possession. The first task is to position a series of survey control points, the equivalent of the wooden pegs referred to earlier. However, as the control points are placed more than two metres away from the tracks, in a place of safety, there is time to fix concrete cones or small monuments with an exposed metal pin.

Once this work is completed, additional targets for the UAV to locate are placed around the site. These are usually black and white crosses on wooden boards or similar. Again, these are positioned outside the two-metre envelope to ensure safe working without the need for costly protection.

These coordinates are then established using normal surveying techniques, such as a total station. Then the Drone comes into action. But the Vogel R3D is no ordinary drone. It has a 100-megapixel camera, weighs about 9kg and, if you wanted to buy one, you would need in excess of £90,000. In terms of drone technology, the Vogel R3D is a very good quality product and therefore has a high level of accuracy – a critical factor when carrying out such a survey.

One of the three operatives is the pilot in charge of what is, effectively, a small aeroplane and has a license issued by the Civil Aviation Authority. Therefore, as might be expected, the pilot carries out pre-flight checks following the appropriate procedures outlined in a 300-page manual to get the drone into the air. The drone is manoeuvred using a combination of GPS and manual control.

The second person’s responsibility is to control the camera and to assist the pilot, ensuring that they avoid any identified hazards. The role of pilot and camera-operator are often interchangeable. The third person’s role is as general assistant, downloading data, charging batteries and managing the site.

Overlapping photographs

For the Salfords track renewal survey, the drone operated at a height of between 25 and 35 metres and was in the air for about 12 to 15 minutes for each flight, with between 10 and 15 flights each day. During the three days, more than 8,000 overlapping photographs were taken, each photograph is about 80MB in size.

At present, there is no measurement capability to determine the size of the images captured. So Plowman Craven uses a well-established process, not dissimilar to techniques used by reconnaissance in WW2, whereby two overlapping photographs intercept a common position and the stereo effect enables the height to be determined. Computer software “Pixel Matching” carries out this procedure thousands of times, enabling a 3D picture to emerge.

3D Point Cloud

A huge series of numbers, each with x, y, z coordinates, provides raw measuring data that forms a ‘Point Cloud’. This, in turn, uses the reference targets referred to earlier, enabling them to match into the survey grid. The 3D Point Cloud is a key element of the process because, once this information is put into CAD software, reality starts to emerge and the welds, joints, rails, sleepers and ballast start to be defined.

All is revealed, as is a very detailed track survey. This work has been carried out, working in a safe environment, without interrupting the train service and at minimum cost. In addition, the process offers a lot more information than that used for the track renewal. Undoubtedly, this additional information will become useful over time, offering a significant amount of additional value.

High level of accuracy

Vogel has now completed five different schemes and is becoming an established option. Also, it is evident that the potential financial savings are significant. The accuracy of the survey is between 0 and 5mm and Plowman Craven is now able to get the accuracy down to a level of 2mm with some consistency. Other drone systems tend to operate at an accuracy of 30 to 60mm.

So what are the next steps? To date, detailed trials have been undertaken to prove the accuracy of Vogel R3D and compare the data to traditional survey techniques. Vogel R3D meets Network Rail’s Band 1 accuracy requirements and is therefore suitable for track alignment and topographic survey at all GRIP stages.

It is exciting times for track renewal engineers and for drone technology. The future of surveying appears to be up in the skies. However, I found it very reassuring that local control points are still required, so the opportunity for banging a few wooden pegs into the ballast might continue.

It really is very therapeutic!


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