To say the terrible derailment at Carmont shocked those running Scotland’s Railway is an understatement.

Staff across ScotRail and Network Rail Scotland were busy – to borrow Scotland’s Railway’s tagline – building the best railway Scotland has ever had. And with recent electrification schemes deliver faster and greener journeys, new trains, new stations and plans for new lines, they’d been making great progress. August 12 hit them hard.

Smoke curly from the Carron Water’s deep valley provided the first sign something was wrong and prompted a call to Police Scotland. At the same time, Nicola Whyte, a ScotRail conductor travelling on the derailed train, was hurrying to Carmont box to raise the alarm.

I salute her clear thinking. She can only have clambered out of the train’s wreckage in shock at the devastation around her. The train’s leading power car was down an embankment; another coach nearby and ablaze. Two more rolled upside down with the fourth balanced on top. Only the rear power remained in line with the track, albeit derailed all wheels.

Old but safe signalling at Carmont

The line through Carmont is one of only a handful of Network Rail’s lines still signalled under ‘absolute block’ regulations. Entirely safe from a signalling perspective, they permit only one train to enter a section of track between two signalboxes. A second cannot follow until the signaller sending it receives confirmation that the first has arrived at the next box. Once a train leaves a signaller’s immediate area, the signalling system does not know precisely where it is; only that it has left one box and has not arrived at another. And it’s just over five miles between Carmont box and the next one north, Stonehaven.

Railway rules require a train’s crew to lay detonator protection to warn and stop other trains approaching. With driver and guard incapacitated, it fell to Nicola to do this and she chose to head for the nearest signalbox, Carmont.

Fortunately, there was no train heading south. Equally fortunately, the derailed train, the 0638 Aberdeen-Glasgow Queen Street returning north, only had nine people on board. If COVID-19 can be praised for anything, it’s that so few people were on the 0638. Realising that three of those nine died, it doesn’t bear thinking about the consequences of a full train.

Landslide derails train

The cause of this wreck appears to be a landslide. Aerial photos show a small slip just back along the track from the mangled coaches. The 0638 is not the first ScotRail train to hit a landslip but it’s the first with such devastating results. Landslips often derail trains but they generally stay upright and in line. An accident report a few years ago showed a ScotRail Class 158 with debris slumped in the foreground. It was running at 45mph and stopped 160m beyond the slip. That same report noted that no-one had died in a train hitting a landslide for over 50 years in Britain. (To emphasise the risk, it added that nine people died when an Italian train hit a landslide in 2010.)

Had the 0638 not hit the parapet of the bridge, it too might have stayed upright and in line. Even if it had reached its 75mph maximum speed for that stretch of line. Just as with Heck in 2000, a small derailment was fatally magnified by other factors. At Heck, it was trailing points that pushed the front of the train into the path of a coal train. I visited that site the following day and the images of sheer devastation still haunt me today.

But back to the problems of landslips. They are not new. The Railway Children in 1905 involved three children warning a train of a landslip so it could stop in time. On the real railway, there’s is a long screen of trip wires alongside the line at Pass of Brander. Should a rock fall down the bank, the wires break. This places a semaphore signal arm at danger to alert any approaching train. This mechanical apparatus has sat sentinel since 1882.

‘Stone signals’ stand at Pass of Brander. Linked to trip wires, they warn of rocks fallen onto the track. PHILIP HAIGH.

What Network Rail needs today is the equivalent of the Pass of Brander’s system to watch over likely landslip sites. Sending an alert to the controlling signalbox, it could provide a way of stopping trains in emergency following a landslide. 

Carmont driver heard alert

NR already has a way of alerting trains. Indeed the driver of the 0638 received a radio alert telling him of flooding ahead earlier on his southbound journey. The flood report came from another driver heading north towards Carmont. However, it’s clear that using trains and drivers to find floods and landslides is not the best answer.

NR knows this and published last year a ‘challenge statement’ with the rather clunky title “Detection of Geotechnical Asset Failure by Means Other than Train Drivers or Lineside Staff”. The statement was a prompt to innovators and research and development teams.

It notes: “Geotechnical failures are frequently reported by train drivers as bank slips or rough rides. This is too late for preventative measures to be put in place”. It adds: “Most data capture requires an examiner to go on site. This is time-consuming and limits the frequency that condition data can be collected. Access to inspect assets is often difficult, especially when accessing through third party land. Some third party assets also pose a risk to the railway, for example slopes outside our boundary and boulders.”

When you consider that NR has 190,000 earthwork sites to inspect you can see the size of its challenge. It suggests the answer might come from frequently scanning earthworks using LIDAR. It would compare runs to detect differences, perhaps where the toe of a cutting is starting to bulge.

Using fibre optics

There might be another answer and that’s to use long fibre optic cables to listen for sounds of movement. This could detect real landslides in time to alert signallers and drivers. It might seem odd that something that transmits light can ‘hear’ but it seems it can.

The Fibre Optic Sensing for Railways Association is a small group of European railway managers. It reports one early use of fibre optics was to hear cable thieves at work and be able to determine their location. It can also hear trains passing so provides another method of tracking where they are, which DB has successfully tested to trigger passenger announcements at stations.

In another trial, a fibre optic cable could distinguish between tamping and grinding work. The association suggests that by merely listening, they can detect when track needs repairing or replacing.

If fibre optics can hear passing trains, or cable thieves, or lineside work and detect their location it seems likely they will be able to hear a landslide and raise the alarm. What intrigues me is that many tracks are already flanked by fibre optic cables. Might they listen for problems while also doing their primary job?

NR’s challenge statement shows that it’s well aware of the problem. I hope that the terrible events at Carmont provide the boost in interest that researchers need to develop fibre optic sensing. It wouldn’t be the first accident to trigger another major step forward in safety but I hope that it’s one that contributes to Britain continuing to be the safest railway in Europe.

This article first appeared in RAIL 912 on August 26 2020.

By Philip Haigh

Freelance railway writer, former deputy editor at RAIL magazine - news, views and analysis of today's railway.