Railway Track Components: What Each Part Does
If I asked a random person in the street to name and explain the components that make up the railway track, they would probably be able to name rails, maybe sleepers and then the stone. That would likely be it.
It’s not be a bad start. To most, the track is something that carries the train that takes them to their destination, like work or the airport. But this does the track a great disservice. A railway track is an engineering system, comprising of multiple components, each with their own specific function. It has been refined and optimised over the decades to increase its performance and longevity, whilst reducing risk.
If you are looking at the track, you can see the rails stretching out in front of you away out into the distance, you will lose count of the sleepers and you can only guess at how many tonnes of ballast (the stone) there are. But you might not notice the pads, insulators and fastenings. You cannot possibly see the formation or membrane layers installed under the surface.
In this article, I’ll explain the main components that make up railway track, what each one does, and how they work together as a system.
What the Track Has to Do
Before we dive into the individual components lets take a moment to look at what the track overall has to do.
The track as a system has a number of key roles:
Guide the train
Maintain the designed track gauge
Support the heavy loads of the trains
Transfer forces
Resist movement
Manage vibration
Be maintainable
Quite the list. But the track system you see from the platform, bridge or side of the track achieves all these things. Not with a single component but through the components we are going to explore below.
Rail
Rails, the component that gives its name to the whole mode of transport.
The rail’s primary function is to give a surface for the train wheel to run on, whilst also guiding that wheel and ultimately the train. Whilst doing this, the rail needs to withstand the high levels of force that come from the train’s mass.
How does it do this? Through its shape. The shape of a railway rail is pretty unique and distinctive. Whilst there is a variation in sizes and shapes, known as profiles, the overall shape remains the same. The top or head of the rail, is shaped to interact with the train wheel profile. Together they work to guide the train along the track. The middle, or web, transfers the force through the rail, whilst keeping the weight of the rail down. The foot of the rail helps spread load into the supporting sleeper below and gives the fastening system a surface to connect to.
The rail has to be tough, it is subjected to high forces and loadings. The steel that makes up the rail has to resist wear whilst also allowing lengths of rail to be joined. Then there is the environment. Rails, like all track components are subjected to all the seasons and the weather they bring. Being metal, rails are particularly susceptible to temperature change. They expand and contract as temperatures rise and fall. This change, and the forces involved, has to be managed by the rest of the track system.
Interested in finding out more about the shape of the rail? Give this video a watch: https://youtu.be/L5z3KrvmWgI
Sleepers
After the rails, possibly the most recognisable component on the railway. Sleepers sit directly below the rails, supporting them. The sleeper is also charged with holding the track gauge, the distance between the rails. They do this through giving a fixed point for the rails to be secured to with fastenings (more on these in the next section). Sitting below the rails also means that the sleeper is an important part of how the heavy and concentrated loads of passing trains are spread and distributed into the rest of the track system, and ultimately the ground below.
All sleepers perform the same basic functions, but the material they are made of is a factor in how well they perform it, their longevity once in track and other characteristics. Examples of this are the mass of concrete sleepers, which gives the track good stability and resistance to movement. However if movement or poor support is present, ballast degradation can be faster. Wooden sleepers, on the other hand, are typically less harsh on the ballast, bring flexibility with the ability to be redrilled easily. But their reduced mass does affect track stability. The other materials commonly seen are steel and the relatively newly introduced composites and plastics.
Want to see in detail how these different sleeper materials stack up against each other? Watch here: https://youtu.be/eO-s4Odq8sI
Or if you’re more interested in learning about the functions of sleepers in more depth, then this is the video for you: https://youtu.be/VUBHNYaANtY
Fastenings
The rails don't just sit on the sleeper, they are secured to it with fastenings. Fastenings are the mechanical link between the rail and the sleeper, helping maintain gauge, restraining the rail and managing rail movement. Fastenings actually covers a number of components that come together to meet these requirements, and the exact arrangement depends on the design.
In some areas of track you may see a baseplate, screwed into the sleeper with an elastic clip holding the rail in the baseplate. On other areas, mostly concrete-sleepered areas, you may see housing for the clips directly cast into the sleepers. In the US, the spike fastening is still very very common. Effectively a big nail, these are driven through a hole in the baseplate, with its head securing the rail.
Many fastening systems apply a clamping force to the rail foot. This is commonly referred to as toe load.
Rail pads and insulators
Pads and insulators are the first of the less obvious components, that you might completely miss when looking at the track. But they have really important roles.
Pads are found under the rail, in the area known as the rail seat. This is where the rail sits, either in the baseplate or on the sleeper, depending on the design. Made of hard rubber, the pad’s role is to provide a softer layer between the hard rail and sleeper/baseplate materials, helping manage vibration along with load transfer. In addition to this management of the vertical forces, pads also help prevent longitudinal movement of the rail, such as from braking trains or thermal expansion.
Insulators are installed between the fastening clip and the rail and primarily, as the name suggests, they provide an insulating layer. Why is this important? Well electrical currents are passed through the rail for a number of reasons (traction return, track circuit train detection systems), and it’s important that none of that current is controlled and does not pass where it should not through the fastening system. Insulators also have another another function where they fill the small gap between baseplate and the rail edge, limiting minor lateral rail movement. To achieve this they come in a number of sizes/thicknesses.
Ballast
Ballast is the biggest component on the railway by a number of metrics; volume, mass etc. It might seem strange to refer to crushed stone as a component but it is there to carry out vital functions.
Ballast sits under the sleepers, supporting them and spreading the load of trains out. It allows water to drain through it, whilst also resisting (through its mass) any movement of the sleepers. So what actually is ballast? It is crushed stone, typically granite, that has an angular shape. This shape allows individual stones to “lock” together, giving it strength.
It is worth pointing out that not all track is supported by ballast, some track is slab track. This is where the sleepers and ballast arrangement is replaced by a fully concrete support structure.
Want to know more about slab track, what it is and where you might find it? Watch here: https://youtu.be/WQFRYSm0cFg
For more on the functions of ballast, this is the video for: https://youtu.be/RcmCLVd5iuI
Formation & Subgrade
Now lets venture below the surface of the track and below the ballast layer to look at the formation and subgrade. The subgrade is the natural ground below the track structure. The formation is the prepared surface or engineered layer that the track is built on. These layers form the foundation for the track. They influence how the loads are distributed into the ground below and how consistently the track is supported over time. Given the variations of ground conditions, these layers can be designed and engineered to improve track support and reduce any variation along the tracks route. This may include a sand blanket layer, the use of crushed aggregates, geocells and membrane geotextiles.
A weak, or inconsistent, formation can lead to reoccurring issues with track quality and require increases levels of maintenance.
Interested in this subsurface part of the track system? Found out more about it, and the options engineers have with this video: https://youtu.be/RC2vjqAlviI
Switches and Crossings
It might seem odd, or even controversial, to have Switches & Crossings (S&C) down as a component in the track. Strictly speaking, S&C is not one component. It is a whole family of components. But, it is important to point out that plain line, is the simplest track arrangement and that other arrangements exist.
S&C allows trains to move from one route, or track, to another. To do this, it uses additional components such as switches, crossings, check rails, stretcher bars, points operating equipment and other components. Different layouts can be used in different situations, from the simple single turnout junction right up to other incredibly complex layouts seen at large stations.
For more on S&C, what is is and why the railways wouldn't be the same without it, give this video a watch: https://youtu.be/hzhPx4p7vc8
What about drainage, bridges and other supporting systems?
You might travel over bridges, see the catch pits of the drainage system from the platform, or pass through tunnels when using the railway network. You might wonder if these are also track components?
There are many other engineering structures and systems that support the track and enable it to carry out its function. Bridges carry the track over rivers, roads, valleys and other obstacles. Tunnels give it a path through hills and mountains, while drainage gets rid of water from the track.
These are not track components in the same way as rails, sleepers, fastenings or ballast. They are supporting railway assets with their own components, but they still have a major influence on track performance.
Poor drainage can ruin track quality. A bridge can define how the track is supported and maintained. A tunnel can restrict access, clearances and maintenance options.
So although I would not describe them as track components, they are part of the wider railway system and interact closely with the track system.
How the components work together
All the components we have discussed so far come together to form the track system.
Rails carry and guide the train wheels. Sleepers hold the gauge while starting to distribute the load. Fastenings hold the rails in place. Pads and insulators help manage load transfer, vibration, movement and electrical separation. The ballast below supports and restrains the sleepers, while taking the load and transferring it into the formation layers. The formation layer then helps manage how that load is distributed into the natural ground below.
That is why track should not be looked at as a list of separate parts. Each component only makes full sense when you understand what it contributes to the track system as a whole.
Why component knowledge matters
So why do you need to know the functions of these individual components, especially the smaller ones that can look insignificant at first?
Because if one of those components fails, is missing, or is not working as intended, the performance of the whole system can be affected and risk can be introduced.
This is where maintenance comes in. To identify an issue and rectify it effectively, you need to understand what each component is and what function it is meant to perform.
This knowledge helps you recognise issues, understand possible causes, consider suitable rectifications, and build a clearer understanding of the track system overall.
If you ever find yourself walking track, looking at photos, reading inspection notes or listening to experienced staff discuss a defect, knowing the components and their functions gives you a much better starting point.
Do you want a guide to help with identifying these track components? Download the free Track Components ID Guide. It is designed to help you recognise the main parts of the track and understand what each one does. https://bit.ly/TrackComponentIDGuide
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