Railway basics

Side cuts

An earthwork on the slope. If tracks need to run along the side of a mountain a side cut needs to be made on the side of the mountain. It allows horizontal track geometry and overall the first line layout. The side cut is, so to speak, a half cutting in combination with half an embankment. On the uphill side, protective retaining walls may be required. On the downhill side, protective walls in addition to the measures to be taken against flying stones or avalanche barriers may be required.

Railway installations

Railway installations include all the fixed installations which are essential for railway operation and safety. A distinction is made between station areas, main lines and other railway premises such as depots, sidings or workshops. Railway installations can be divided into sites, including the track formation, buildings and other premises, as well as the places required for tele-communications, protection, process control technology and the power supply.

Side ditches

The track formation must be effectively drained. Side ditches (gutters, hollows) are provided for the drainage of the surface water resulting from rainfall. They can be open or covered and always have a slight longitudinal inclination. In cuttings there are two ditches. One on the left and one on the right of the route at the foot of the track formation, in side cuts there is only one (on the uphill side). The dimension of the ditch depends on the expected precipitation. If the groundwater level in the area of the route is lowered or the soil completely drained, covered deeper drainage ditches are built ("deep drainage"). Drainage systems must be regularly checked and serviced.

Track formation

The track formation is the part of the railway installations that carries the rolling traffic. It forms the carriageway. Technically, the track formation is divided into the subgrade(e.g. an area prepared to compensate for unevenness, if necessary, and the solidified foundation soil) and the superstructure(e.g. ballast and track). The track formation also includes bridges and tunnels, walls and other engineering structures. Depending on the local situation, a distinction is made between road bound track formation, special track formation (in public transport, but separated), independent track formation or separate track formation. The latter is the normal case in railways.

System overview
Terms for ground construction


Any rain water must be removed from the track formation, otherwise it will become sodden, and scouring and frost damage will occur. A well-functioning drainage system is very important, because it gets rid of the water. Because of its importance, drainage must be regularly serviced, reviewed and  flushed if necessary. There are shafts provided for this at intervals of 40 to 50 m.


A cutting is an earthwork responsivle for lowering the track level below the surrounding land. Deeper cuttings replace tunnels where possible, but require a larger intrusion in the landscape due to the considerable earth removal and sufficient sloping sides. Material from the cuttings in hilly terrain is used in the adjacent embankments. Prime examples of routes with rapid sequences of cuttings and tunnels, embankments and bridges are combined fast passenger and freight lines with minimal gradients (e.g. Hanover-Würzburg,  Mannheim-Stuttgart, Germany).


The track takes all the static and dynamic forces in all three dimensions that come from the vehicle when it is in operation. It carries vertical forces and sets horizontal longitudinal and transverse forces against reaction forces of the same size. The track is designed to cope with all the operating conditions and, in addition, have enough safety.

Catenary masts

Catenary masts are usually situated on both sides of the route and carry the entire contact wire system. On the railways, the cross spans are anchored onto the masts. They support the carrying cable which runs along the track and holds the actual contact wire. At selected points the catenary system must also be anchored in the longitudinal direction to masts. The so-called curve deductions on the transverse carriers give the contact wire line in curves the shape of a polygonal trace. The mast locations are adjusted to match this. All cables need to be insulated against the masts. Feed lines are carried on the top of the mast and on the back of the mast there are also return lines. Catenary masts can be made of steel or reinforced concrete. Catenary masts made of wood are no longer common, but still used on branch lines.


The railway infrastructure is specified by the permanent way. Its features and components are the track and its line with all turnouts and crossings. In the layout of the line of the infrastructure, on one hand, geological conditions (the type of terrain, subsoil) as well as structural solutions (cuttings, embankments, bridges, tunnels, curves, fillets) and, on the other hand, the performance of the proposed rail vehicles must be taken into account. All the components of the infrastructure form a network, which can be self-contained (e.g. in the case of narrow-gauge railways or in urban areas) or can be internationally connected.

Vehicle ride

The so-called "vehicle riding" depends on the interaction between wheel and rail, or more exactly the wheel profile and the rail head. Smooth riding of rail vehicles is characterized by a quiet, constraint-free sinusoidal run of the wheelsets in a straight track. In the curve, the wheel - dependent on the running gear and vehicle design - performs a longitudinal and transverse movement on the rail head which results from the different radii of inner and outer rail. Centrifugal forces can be limited by superelevation of the outer rail. For smooth vehicle riding regular inspections and, where appropriate, repair work on the profiles of wheel tread in combination with flange and rail head is required.


Geosyntheticsinclude fleeces (pressed fibres) and geotextiles (interwoven fibres). While fleece, used above the formation protective layer, has a filtering effect, geotextiles are laid below the formation protective layer. They are designed to improve the load-bearing capacity of the formation and also have a water blocking effect and divert it sideways. Geotextiles have been used since about 1985 and are put in from a roll. Exposed ends of the plastic sheeting decompose under the influence of UV radiation in approximately five years.

Loading gauge

The loading gauge is the area in the cross-section of the railway track, which must be kept free from any fixtures. Nothing must project into the “loading gauge”, on the other hand vehicles including their loading, must not exceed it. Rails, sleepers, catenary masts and overhead line equipment, tunnel walls and railings, as well as platform edges are located just outside the loading gauge. The loading gauge also considers all side vehicle movements during the journey or conceivable geometry faults of the track. Vehicles must be able to run without any risk of crashing and without any difficulty. Within the loading gauge there is the - tighter - vehicle gauge. The standard clearance gauge specified in the Railway operating instruction is larger than the loading gauge is. It contains safety spaces and space for installations that are necessary for operating that project into the standard clearance gauge.


The "superstructure" includes all components of the track structure above the formation. In particular, the ballast bed, the track grid (sometimes also called rodding) consisting of rails and sleepers, as well as turnouts and crossings, including, where appropriate, track coverings and crossings. The track structure requires regular maintenance, in order to fulfil ist tasks.

Overhead line system

The overhead line is the last component in the power supply system. The catenary wire, also called the copper conductor, is usually located at a height of 4.95 to 5.75 m above rail level (upper surface of the rails). In order not to destroy the pantographs, the overhead line is arranged in a gentle "zig-zag" path, thus it is slid over by a 50 to 75 cm wide area of contact slip surface of the pantograph. 


The formation (also called subgrade level) is the ground surface prepared to support the track surface. It is the top layer of the extended subsoil. A subgrade protection layer applied to the formation is an integral part of track construction today.

Formation protective layer

The fine-grained formation protective layer  is applied on the formation, possibly on an additional layer of geosynthetics (geotextiles). It is also called "track bed layer", because it is intended to increase the load-bearing capacity of the soil and can be used for soil improvement with a lime-cement mixture.


There would be no railway without rails. There is a variety of different rail sections, some of which have limited use (e.g. crane rails). In principle, each rail is a rolled, long steel beam. The widest part is always the rail foot and above it there is the rail web and at the top of this there is the rail head. The rail foot is located next to the sleeper. Where appropriate, it is separated by an elastic rail pad. If rails are connected by bolted joints, holes are provided in the rail web and the rail ends are connected by steel bolts in the "fishplate surface", which connect the fishplates. Normally, rails are continuously welded today.

In general usage, "rail" and "track" are often used as synonyms, but this is not correct. In general, the track is formed of two rails with sleepers and ballast or slab track. In special cases such as the integration of narrow-gauge railways, the track can have three or even four rails. Routes with just one central, paved guide rail, have been laid for rubber tyred vehicles similar to bus and coach lanes especially in French cities.

Rail fastening

Rail fastenings ensure safe, predefined values to keep the rails attached to the sleepers. The rails can simply be nailed (remember the "golden spike" at the end of a railway building project in the USA[1]) or fixed with screws directly on the sleeper. Today's standard rail fastening systems rely on an indirect attachment by screws and spring elements (clips). All the fastening and connecting devices fall under the railway term "track fittings". 

[1] Translator’s Note: For Americans in 1869, the driving of the golden spike, which joined the Union Pacific and Central Pacific railroads at Promontory Point, Utah, on May 10, carried a significance similar to that of the first moon landing for a later Generation.


Ballast is composed of hard rocks with sharp edges and a particle size of between 32 and 65 mm. It is broken in special ballast plants. It is important that the particles have sharp edges so that the ballast bed can provide a secure location in the ballast bed. The materials used are granite, diabase or basalt. Different materials are used from region to region. The quantity of ballast required per metre of track is 3.5 to 4 tonnes on average, which is slightly more than 2 m³. After about 30 to 50 years, the ballast needs to be completely renewed.

Ballast bed

The ballast bed carries the track grid and ensures that it is retained in a stable position, but at the same time must be elastic and enable a certain amount of track deflection under load. In addition, the ballast bed must allow rain water to drain away effectively. Regular maintenance of the ballast bed (use of tamping machines, with selective hand tamping at certain points) ensures that it retains its properties. At longer time intervals, depending on load and ambient conditions, the ballast bed must be cleaned partially (humus, abrasion; the use of ballast cleaning machines), or completely replaced (use of track renewal trains). Inadequate maintenance reduces the carrying capacity of the track bed, leading to the introduction of speed restrictions and finally up to the destruction of the ballast.


The sleeper laid transverse to the direction of travel in general keeps both rails parallel to each other, distributes the load and ensures the correct track gauge. Typical forms are the classic wooden sleeper, the steel-reinforced concrete and steel sleeper, as well as the so-called Y-steel sleeper. With the so-called bi-block-sleeper two concrete elements are connected under the rails by steel rods. This design has a greater lateral displacement resistance. Wooden sleepers are unsuitable for tunnels (because of humidity problems); for bridges over water they are only permitted without impregnation. In addition, for some years now different types of plastic sleepers made of glass fibre bundles, with steel inserts or endlessly extruded from recycled plastics have been available. On steel bridge constructions, fixed sleepers are called bridge beams. Unlike regular sleepers, they have only two supporting points. Some crossing timbers can have a considerable length. There is also a so-called hollow sleeper, on which the equipment for point heaters or actuating rods is mounted. Sleepers lying under both rails along the direction of travel, which require additional tie rods or other elements to maintain the correct distance apart are also designated as Long sleepers; they can also be concreted (type of ballastless track).

Soled sleepers

In the case of concrete sleepers, it may be useful to "give them an elastic pad". During the manufacturing process it is normal that a pad of polymer materials is put on the still damp concrete (the top side becomes the underside of the sleeper when removed from the mould). This resilient elastic pad increases the contact surface on the particles of ballast, ensures the positional stability and at the same time prevents damage by stones, since concrete sleepers are vulnerable to any point loads caused by stones. In addition, the ballast will have a longer life. Sleeper padding solutions are particularly important if a bituminous track bed layer is required below the ballast because this is less elastic.


The track gauge is defined as the narrowest point between the sides of the running rails of a track that face one another. It is measured at a height of 14 mm below the rail track running surface, with a "standard gauge" it is 1435 mm. In normal operation the dimension of standard gauge railways is permitted to be between 1430 and 1470 mm; with trams and light rail vehicles this range is smaller. In curves, especially curves with small radii (on railways: below 175 m), the gauge is increased in the interest of a smooth running in 5-mm increments up to a maximum of 1,450 mm.


The track lies on the subgrade that has been prepared and is able to support more load. It possibly has a supplemented height of subsoil (formation). The upper side is called "formation"; the subgrade is called “extended track”. If necessary, it evens out level differences between planned line layout and augmented subsoil.

Rail pads

The rail pad is part of the rail fastening and is located between the rail foot and the ribbed plate mounted on the sleeper. In the past, 5 mm thick poplar wood was used as a rail pad, as it had good suspension properties and a long service life. Today's rail pads consist of plastics (polymers). They have angled edges on both sides to prevent them from slipping. Rail pads must be changed at certain intervals - depending on the traffic approximately every five years - in order to ensure that the track is in good working order.

You can find suitable specialist literature about the topic here:

The Railway System (German)

Handbuch - Das System Bahn

Railway systems are highly complex structures. This is characterized by a variety of internal and external reactions between the subsystems and their environment.


The close links with housing developments, economic and transport structures represent, on the one hand, the external reaction of the rail system with the environment and, on the other hand, the muliple internal reactions between the parts of this system, such as between infrastructure, rolling stock and management. Over the past few decades, due to rapid advances in electronic data processing, these reactions have become more complex and complicated. A holistic view of the rail system is therefore essential.

Railway Signalling & Interlocking

Railway signalling is one of the few technical fields which are still mainly oriented nationally. However, the international aspect becomes more and more important. The purpose of this book is to give a summary and comparison of railway signalling and interlocking methods at the international Level.
The contents cover the whole range of signalling equipment and methodology.


Schachner, W.: Schulungsunterlagen Oberbau für Einsteiger. PMC Rail International Academy, Bingen 2017.

Göbel, C., Lieberenz, K. (Hrsg.): Handbuch Erdbauwerke der Bahnen, Planung Bemessung Ausführung Instandhaltung. 2. komplett überarbeitete Neuauflage 2013. Hamburg: DVV Media Group Eurailpress. ISBN 978-3-7771-0430-0

 Matthews, V.: Bahnbau. 7. überarbeitete und aktualisierte Auflage 2007. Wiesbaden: B. G. Teubner Verlag/GWV Fachverlage. ISBN 978-3-8351-0013-8