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The Railway infrastructure - The most important part of the railway


The infrastructure in the United Kingdom

Currently there is nearly 10,000 miles of track, serving 2,500 stations in the United Kingdom. Based on this, it's pretty likely you have a train station near you right now. 

The Infrastructure consists of rails, fastenings, ballast, sleepers, switches & crossings, signals, signs, fences, and many more parts.
Most of the rail network in the UK is served by Network Rail, however many contractors also work upon the railway, often appointed by Network Rail. 
Network Rail also control the safety regulations upon the railway, including the provision of Personal Track Safety Cards.

Components of the Track

The railway in the United Kingdom consists of many parts, which include;

  • The Rail
  • The Ballast
  • Drains
  • Sleepers
  • Fastenings (Pandrol Clips, Fishplates, Steel Keys, Insulators)
  • Signals
  • Electrification equipment

Each component of the track is extremely important, and without it a safe railway could not function. It is also extremely important that each component be installed correctly, using components that have passed inspections, are certified for use, and correct for use based on the type of track, sleeper, etc.

Bullhead and Flat-Bottom

Bullhead and Flat-Bottom


There are two main types of rail currently used on the British rail network; Bullhead and Flat-Bottom, which are both typically manufactured from wrought Iron. They both require different types of fastening to maintain the Gauge/positioning.
All rails have markings on them, telling the track-men, where the rail was manufactured, and when, and from what material, etc.
Both types of rail have a;

  • Head; where the wheels of a train rest upon the rail
  • Foot; The bottom of the rail
  • And a Web, the area in between the head and the foot.

Bullhead - Bullhead rail is one of the oldest forms of rail currently used in the UK, however it has largely been replaced by Flat Bottom Rail.
Bullhead rail is top-heavy, meaning that if left to stand alone it will topple over. As a result it will have to sit in 'Chairs' that are attached to the sleepers in order to keep their positioning. Whilst in the Sleeper Chairs, the rail will be supported by Steel or Wooden Keys, or often a Panlock Key, all of which are installed with the use of a 'Keying Hammer'.

Flat-Bottom - Flat Bottom Rail is a more common and more modern rail in the British rail Network. It has a flat-bottom, hence it's name and as a result can stably sit on the floor without falling over, however to ensure the rail is kept in the correct positioning the use of fastenings is used.
Flat-Bottom rails often use Pandrol Clips and Fast Clips to connect itself with the sleeper, but other fastenings, such as 'Elastic Spikes' have been used, depending on the type of Sleeper Chair that is being used to connect the rail and the sleeper.

CWR - CWR, or Continuously Welded Rail is now commonplace within the British Rail Network, and has been since the 1950s. It is made from Flat-Bottomed rail. Instead of being connected by fish-plates, CWR is made up of many rails all welded together. This makes for a railway that needs less maintenance, has a smoother trains and allows for faster trains. To prevent buckling, CWR will often have a series of breather switches, that allow for expansion and contraction within the CWR. It will also require 'stressing', to prevent buckling. Stressing is done using Rollers and Hydraulic Equipment.

Regular ballast

Regular ballast


The ballast is the formation of rocks/stones that are under the rails/sleepers. Ballast has numerous functions within the railway, and is one of the most important components.
Ballast has numerous functions, which include;

  • Provide vertical and lateral stability to the track
  • Drain water adequately
  • Allow the track to be adjusted by manual or mechanical means
  • Adequately spread the load to the next layer in the track substructure

Ballast must be packed under and around the sleeper to be effective, and must be packed within 375mm from the centre of the rail beneath the sleeper, or else the sleeper runs the risk of snapping under the weight of a passing train. Ballast itself must be angular, strong and durable to work effectively. It must be free from debris and free draining as well, or else the creating of 'wet-beds' and other problems could form, which is both costly to fix, and dangerous to trains.

Ballast itself is made from granite, and in England comes from many areas, however the main quarries are located in Wales and Leicestershire. Blue/grey tinted ballast comes from Wales, pink tinted ballast comes from Leicestershire.

Catch-Pit with Cover

Catch-Pit with Cover


Whilst drainage itself is not a specific component, it is made up from a series of components.
Draining on the railway is extremely important, and adequate drainage prevents problems such as wet-beds arising.

The components of drainage include; Ballast, The Formation, Geomembrane, Catch-pits, and Drains. We have already covered Ballast, which allows water to flow through it self and not settle on the top layer of the track.

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The Formation - The formation underneath the ballast allows water that has flowed through the ballast to run off to the nearby drains. The formation usually has a slight crossfall of 1:20. As a result no stagnant water is able to stay around the track, assuming the ballast and formation has been properly installed and maintained.

Geomembrane - The Geomembrane is a polymer sheet under the ballast but often over the formation. It assists drainage and allows water to run towards the drain. It is not always present.

Catch-Pits - Catch-Pits are created from a series of concrete rings that are built up from the bottom up. These allow access for drainage purposes every 30 or so metres. Most Catch-Pits have sumps, which collect the silt from drains and prevent them from becoming blocked. The silt and debris can be removed with the use of a Drainage Ladle. Without Catch-Pits drains would often become blocked and would need more maintenance themselves. When working in an area where Catch-Pits are present, extra care must be taken to ensure the lids/covers are properly placed on the Pits, or someone could fall down them.

Drains - Drains take water that has flown through the ballast and down the crossfall away to a different location. They can be made from a plastic PVC material or concrete. Drains can be located in the 6-foot, 10-foot or Cess. Drains can run towards numerous locations, such as nearby rivers, lakes, or water-recycling centres.

Steel Railway Sleepers

Steel Railway Sleepers


Sleepers have many purposes; including to support and distribute the weight of the train, keep the gauge and support the rails themselves. They are used as a base for the tracks, and are laid transverse between the rails. There are 4 different types of sleeper; Hardwood & Softwood, Concrete Sleepers, and Steel Sleepers.

Wooden Sleepers - The most commonly used railway sleeper. They are made from Hardwood such as Oak and Softwood. Originally stone sleepers were used, however wooden ones were found to be more able to support the track. However they are susceptible to rot and insect infestation if not correctly treated. Other problems include wear from chairs, etc and splitting. As well as this often the fastenings/spikes will work themselves out of the sleeper.

Concrete Sleepers - These are made from reinforced concrete, and were implemented more commonly after World War 2 as materials were scarce in some areas. They are better able to support the rail, and are extremely durable and last longer than wooden sleepers. However they are nearly twice as heavy as wooden sleepers, meaning they are more difficult to replace. Pandrol clips are often used as fastenings on concrete sleepers.

Steel Sleepers - These are fast becoming the most popular choice for sleeper, with their ability to handle weight and loads extremely well. They are very cheap and economical and also last for longer than steel and concrete sleepers. As well as this they are lighter than concrete sleepers and are easier to install. The steel sleepers are 100% recyclable, and require 50% less ballast than concrete and wooden sleepers. Fast-Clips are often used on these sleepers to connect the track to the sleeper.




Fastenings are what connects the track to the sleeper, the rails together, etc. Without fastenings the track would not be able to keep it's gauge, and trains would derail. There are hundreds of types of fastenings used on the railway. So many that naming them all would be nearly impossible, so here I will mention the ones most used on the railway.

Fishplates - These connect the rails together. They must be oiled regularly. There are many types of Fishplates, including Flat-Bottom Fishplates, Bullhead Fishplates, insulated joints, etc. They are only used in jointed track, and not CWR. Between the two rails there is always an expansion gap, as rails expand and contract depending on the weather. To install them you will need a Fishplate Spanner, and a series of Fishplate bolts.

Pandrol Clips - These are used to connect the rail and the sleeper. They are only used on Flat-Bottom rails. They will require a Pan baseplate when used with Wooden Sleeper, however concrete sleepers usually accommodate for Pandrol Clips. They are installed using a Pan-Puller.

Elastic Spike - These spikes go through the sleeper chair, and directly into the sleeper, much like a bolt.

Steel/Wooden Keys - These hold the rail in position by creating a tight lock between the rail and the Sleeper Chair. They are installed and removed using a Keying Hammer.

Fast Clip - These are fast becoming the fastening of choice for British railways and are manufactured by Pandrol. They are strong, and easy to install. They are installed using a Fast-Clip Installer and removed using a Fast-Clip Extractor, however can be installed with the use of specialised machinery.

Chair Screw - These are for use with Bullhead Rail Sleeper Chairs. They fasten themselves into the sleeper with the use of a Ferrule. They can be installed by using either a T-Spanner, or an Impact Wrench.

Rail-Pad for a Concrete Sleeper

Rail-Pad for a Concrete Sleeper

Other Track Components

There are thousands of other components of the railway, each serving a purpose.

Rail-Pads - These sit between the rail and the sleeper, and are made of rubber. They're used to cushion the sleeper, and act as an electrical insulator.
The three functions of a Rail-Pad are;

  1. To cushion the effect of the vertical loading on the sleeper
  2. To act as a longitudinal spring that assists in the distribution of traction and braking forces along the rail.
  3. To provide electrical insulation.

Ferrules - These are inserted into the holes in Sleeper chairs and create traction between the Chair Screw and the Sleeper Chair. Typically they should protrude 6mm from the top of the hole in the Sleeper chair, to ensure the correct tension is achieved.

Insulators - These are placed at the foot of the rail. They assist in the positioning of the rail and also separate the rails electrically, something very important when using Concrete Sleepers that have been reinforced with steel. There are many designs but all have the same function, and are installed using a Pan Setter.

A Semaphore Signal

A Semaphore Signal

Colour Light Signal with Route Indicators

Colour Light Signal with Route Indicators

Axel Counters

Axel Counters


Signals are extremely important, telling train drivers when to go and stop, or to proceed with caution, and when they're about to cross onto another piece of track. There are two types of signals, coloured light signals and semaphore signals (Which have a red and yellow arm). Signals are controlled through many means, including the Signaller, and Track Circuits.

  • Manually - These are controlled manually by the signaller in a Signal Box.
  • Semi-Automatic - Can through the passage of a train over Axle-Counters, or by the Signaller.
  • Fully Automatic - Controlled only by the passage of trains.

Signals are usually placed on the left hand side of the track, where the driver of a train is positioned, however they can also be positioned above the train upon a Gantry, or on the ground.
A Red signal means 'Danger' and tells a driver to stop, a Yellow signal warns a driver of a red signal ahead and tells them to slow down ready to stop. However a green signal allows them to proceed ahead as it is clear. Some signals have 'Route Indicators' which tell a driver when they're about to pass over to another track. These are made up of a series of small white lights in a diagonal line.

Axle Counters - These are very sensitive pieces of equipment that count the passage of train wheels that pass by. They count them in, and then further along the line count the wheels out. The signals will remain at danger until all wheels that have been counted in have been counted out. As these are so sensitive no tools must be brought within 12 inches of an axle counter.

Track Circuiting - This requires an electrical current to run through the track, and when trains are not running on the line, the rails complete a circuit and the signals are green. However, when trains are on the line the circuit is broken and the signals are set to danger. If a problem arises on this type of track, a 'Track Circuit Clip' may be applied which will set the signals to Danger.

Every signal has it's very own unique number, which is spoken phonetically; i.e. TT621 would be "Tango, Tango, Six, Two, One"

Over-Head Line System

Over-Head Line System

3rd rail, with Contact Shoe mounted upon the train

3rd rail, with Contact Shoe mounted upon the train

Electrification Equipment

Many modern trains are now electrically powered, and as a result need a power supply. Luckily this power supply can be delivered to the train through the use of electrification equipment. However, it is extremely dangerous, and must be considered live at all times. If the power is required to be turned off when working in an area with electrification equipment, the ECO (Electrical Control Officer) must be contacted.

The equipment consists of many different components, and is split into 2 different categories, AC (Alternate Current) and DC (Direct Current).

AC Electrification Equipment consists of Overhead lines, and carries approximately 25,000 volts at a time for trains, but only 1,500 volts for Trams, as a result of which, you should never come closer than 9ft to an overhead line system. The train sports a 'Pantograph' which allows the train to receive the electricity. Components include;

Gantry - This is a structure that helps suspend all the equipment , to keep it approximately 15ft off the ground. Each Gantry structure has it's own unique identification number.

Catenary Wire - These wires are kept at a mechanical tension to stop the wires from breaking as the pantograph travels underneath. This is usually done with the use of weights. Droppers hold the Catenary Wires and Contact Wires together.

Contact Wire - This is what the pantograph makes contact with to receive the electricity that is needed to power the train.

Headspan Wire - These give extra support to the contact wires and other electrification equipment.

Insulators - These are used to electrically insulate the Gantry and other parts of the Overhead Lines from the Contact wires, etc.

Red-Bonds - These are to be considered live at all times. They return any unused electricity to the power-lines so no electricity is wasted.

Direct current is achieved using a 3rd Rail system. Sometimes, such as is the case within the London Underground, a fourth Rail system is used. The 3rd/4th rail carried between 650 and 750 volts. The train collects the electricity through the use of a 'shoe' on the underside of the train. The 3rd rail is easily identifiable, as it sits upon pots, and is slightly raised above the running rails. When working in an area where 3rd Rails are present, approved insulated tools should be used, and only approved insulated personal protective equipment (PPE) should be used too. When crossing a 3rd Rail, the safest bet would be to find a 'section gap' where the 3rd rail stops for a few metres. Failing this, an area with protective boarding should be used. Or if none of these can be found, one large step over both the running rail and the 3rd rail will suffice.


Ryan Palmer (author) from In a Galaxy far, far away on March 31, 2014:

Jawad and AshBash, thanks for the feedback, and happy to hear it helped.

jawad on January 31, 2014:


Did you do your P.T.S exam on the computer or was it on the paper.

I'm just worried about the exam that I have it on 25 of FEB.

AshBash on January 13, 2014:

Great. This helped me pass my PTS and TIC. Thanks.

jawad on January 09, 2014:

Very helpful , and thank you very much for posting this. Hopefully this should help me with my PTS exam and with the course work . Thanks

Ryan Palmer (author) from In a Galaxy far, far away on November 09, 2011:

Awesome, I'll check that out!

ParfaitG on November 09, 2011:

Thanks Ryan-Palmsy for this very informative piece on railway infrastructure. Many believe this technology is outmoded and archaic, essentially "low-tech" but China and Japan are showing novel approaches to railways. China is using state of the art traction transformers and switchgear. Japan is using fuel cells to make high speed rail even faster. IBM is synchronizing timed headways. ABB is installing electrification systems. Siemens is launching 21st century locomotives and rolling stock. See my website on which gives a space to talk about infrastructure across the spectrum from airports to water pipes.

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