Behind the Scenes – What Causes Railway Delays

So, as you may be able to tell, I’m struggling for content given the ongoing pandemic restrictions, so this week I’m going for something completely different. As you may know, I work in the railway industry and this post is going to explain in a bit more detail what causes various delays and causes railways to go wrong. Network Rail has a great website with a series of ‘delays explained’ pages, so for more detail, head over to those and check them out.

This is the one that people love to hate, especially the popular press. There are many ways in which weather can impact the railways, from rain and snow to the infamous leaves on the line and ‘wrong type of sun’.

Snow – The main issues caused by snow, depending on the amount, is either points being blocked or snow drifts completely blocking the line. Points work by having ‘switch blades’ which move and direct trains in the desired directions. In each position, points have one blade flush to the rail, with a gap between the other blade and rail. If/when snow gets into this gap, it can block the movement of the blades, preventing trains being directed down certain routes.

One of the Network Rail snowploughs – photo from Network Rail

The other main impact of snow is routes being blocked by snow drifts or large amounts of snow. If snow is more than 30cm deep, its not safe for trains to run (due to the potential for obstructions to be hidden) unless they are fitted with snow ploughs. Network Rail has a fleet of large snow plough attachments that are strategically deployed across the UK ahead of the winter weather.

Ice – Winter weather usually causes more impact on the railways from ice than snow as temperatures drop more frequently than snow fall. The biggest issue with ice, is if it coats the third rail or overhead lines which provide trains with power, therefore blocking the transfer of electricity. With most trains having a single source of power, if they can’t get the required electricity they aren’t going anywhere.

Icicles in a tunnel mouth– photo from Network Rail

The other impact of ice is the formation of icicles in tunnels and under bridges, and these can seriously damage trains or infrastructure and so services are usually paused until the icicles are made safe.

Leaves – This is a contentious issue, but something that can be very serious. The contact area between a train wheel and the rail is around the size of a 50p coin, and its this lack of friction that usually allows such heavy objects to travel at high speeds.

One of the trains Network Rail uses to clear the lines of leaves – photo from Network Rail

Unfortunately when the wet mulch of leaves coat the rails, this small amount of friction completely goes (think about how you can slip if you step on wet leaves), meaning that trains struggle to start and if they are already moving, struggle to stop. This means it takes longer for trains to depart from stations and have to brake earlier, all of which extends journey times and cause delays. Network Rail operate 61 trains around the network to blast leaf mulch away with high pressured water jets, and in 2019, these trains covered 895,217 miles.

Sunlight – As you’ll know from driving a car, sunlight means you can struggle to see traffic lights, and its no different for train drivers being able to see signals. The other thing train drivers can struggle to see if the sun is shining in the wrong direction are the screens/mirrors that enable them to see the platform train interface (PTI), and therefore they can’t safely depart a platform.

Some train dispatch equipment – photo via Wikimedia Commons

PTI incidents are one of the most frequent type of incidents on the railways and in the worst cases people can die or be seriously injured and so it’s something that is taken seriously. To combat this problem, additional staff can be deployed to assist the driver, but for long trains or curved platforms this is staff intensive and also takes longer than usual to safely dispatch the train.

Signal Failures
For this one, I’m not going to get too specific, partly because I’m not a signalling engineer and partly because signalling systems can get very complicated. However, the key principle of signalling safety is that the system ‘fails safe’ meaning that if it does fail, train movements will stop and therefore still be protected and safe. In the simplest terms, it means if there is a failure, a signal will go red and stop trains, rather than going green.

The West Midlands Signalling Centre

Points Failures – Described in its simplest terms by Network Rail as “a fault with the moveable pieces of track or their operating equipment”. These faults can range from something, such as litter, blocking the movement of the switch blades, to the motor that moves these blades failing. Failures can also occur if the signalling system can’t detect the position the points are in or whether they are locked in place.

Detection Failures – Network Rail describe these as when “the system cannot determine where trains are located due to an electrical issue such as a short circuit on the track or a faulty cable”. For the most part, the signalling system works by sending a small current through the running rails (i.e. not the high voltage 3rd rail). When a train is present the circuit of the current is cut short, indicating the train’s location to the system. Unfortunately, this system means that if the circuit is cut short for any other reason (water, shopping trolleys etc), the system will think a train is present and set signals to danger to protect it.

A work desk at the Three Bridges ROC – photo via Network Rail

Power Failures – These can affect a larger area than most signal failures, especially if the power failure is at the signalling centre rather than local to the signals. Generally signalling systems and control centres are provided with back-up uninterruptable power supplies (UPS), however sometimes these unfortunately also fail, sometimes at the same time as the main power supply. The York Rail Operating Centre (ROC) controls signals as far south as Bedfordshire, as so if a power issue affected York, the impact and delays would soon mount up.

Crewing Issues
This is something I have plenty of experience of as my job involves ensuring each train has the correct crews on board and resolving any crewing issues. Crewing issues can come in two forms, standalone issues caused by crew becoming unavailable for that specific train for X reason, or knock-on issues caused by a more major incident.

Some of the Avanti West Coast crew in front of 390119 ‘Progress’ – photo from Avanti West Coast

On the London Underground, Train Operators tend to operate two or three different trains throughout their shifts, with each train having up to a dozen different operators throughout the day. If any one of these operators become unavailable, it will impact on the crews either side, and depending on timings, can impact on the others trains those crews are due to operate.

Standalone Issues – Imagine a train operator has been feeling unwell, and despite attempting to come to work, has to call in sick about 25 minutes before they are due to start work. By this point, the train they were due to operate, has already passed us on its way to a branch, and the next opportunity to put it into a siding or depot is when it gets back to us (when the operator was due to pick it up).

Some of Northern’s train crew – photo from Northern

If we’ve not got a spare operator available, then the operator on the train will have to stable the train and then make their way back to us for their break. At a weekend, a train operator can be scheduled as little as 40 minutes off a train for a minimum break of 30 minutes, and at my location it’ll take about 25 minutes for them to stable a train and walk back to their break location, leaving 15 minutes for their 30 minute break.

These breaks are there for safety, to reduce fatigue, and so we need to delay the next train that operator is due to pick up until they’ve finished their break. If we can hold it somewhere it won’t impact the service we will, but if we can’t this train will also need to be stabled thus starting the loop again.

Crewing issues can mean trains being stabled in depots – photo from GTR

Knock-on Issues – These are the big ones, that can cause delays and cancellations hours after the initial issue has been resolved. The more complicated a line or company’s network, the more a small issues miles away is likely to impact other services. For example, if due to a points failure, a number of trains are stuck on a branch, you wouldn’t think that this would have an impact on the rest of a line.

However, if the operator at one of those trains was due to be relieved, have their break, and then pick up a train not affected by the issue, this second train could end up being delayed or cancelled with the issue then spiralling. With some London Underground lines having 78 trains in service at any time, these issues can escalate into major issues.

A CrossCountry Voyager departing Derby

Hopefully this post has been useful and given you a bit of background to why things go wrong on the railways and what causes the delays. Everyone who works on the railway is dedicated to keeping trains moving, but the number one principle is safety, and this must come above everything else. If you have any questions about other things that go wrong, please get in touch and I’ll try to answer or do another similar post.

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