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.

Railway Station

According to the German Railway Construction and Operation Regulations (EBO), a railway station is a railway facility with at least one switch where trains can stop, start, end or turn around. Lines can be single or multi-track.

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

Level crossings

According to EBO § 11, level crossings are crossings of railways with roads, paths and squares at the same level. At level crossings, railway traffic has priority over road traffic. The priority is to be marked by erecting St. Andrew's crosses.

Belgrospis

Belgrospis, a rail defect, refers to crack pockets that occur at intervals of 20-100 mm and are due to rolling contact fatigue. The damage is mainly observed on rails that are used at speeds of more than 200 km/h. It only occurs in conjunction with corrugation damage. Its extension is 5-15 mm. When viewed from above, the crack nests have a crack angle of 45° to the longitudinal axis of the rail and run obliquely into the interior of the rail.

Ballast

Layer of track ballast applied to the surface of the base and protection layer or the subgrade for load distribution, damping, drainage, aeration and regulation of the track position.

Embankment

An earthwork with an inclined ground surface of soil or rock created by removal or application of material.

Brake weight

The so-called braked weight, which is given in the unit t and is inscribed on the rail vehicles, is neither a mass nor a weight. It is an evaluation parameter for the braking capacity of a vehicle, which is dimensioned for easier calculation. It is used to determine the braking capacity of trains, also of inhomogeneous trains with different vehicles and with different brakes.

Digital twin

A digital twin is a digitised image of real plants, processes or systems that is composed of data and algorithms. The digital twin is coupled with real objects via sensors and thus connects the virtual and real worlds through information and data. A constant exchange of information and data in real time is thus guaranteed.

Digital twins are used to carry out complex analyses and simulations and to monitor systems. For example, problems can be detected and dealt with before they even occur. This avoids downtimes. In addition, a digital twin offers the possibility to develop innovations and plan them with the help of computer simulations. New products or production processes can be tested in virtual space before they are implemented.

Drainage

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.

Cuttings

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).

Earthworks

Earthworks are earth structures, retaining structures and culverts as well as those installations that are additionally necessary to maintain the functionality of earthworks, including surface protection, fall protection and drainage installations. The earthworks thus represent an essential component of the roadway. In the case of mountain and hilly railways, mass balancing is the aim, and in the case of lowland railways, earthworks are built in a light embankment position to ensure adequate drainage. In order to be able to operate the railways safely and without operational restrictions, the earthworks must be designed to be both stable (load-bearing) and low-deformation (serviceable). The earthworks of the railways must be designed and constructed in such a way that the load-bearing capacity and serviceability of their structurally effective and safety-relevant components is guaranteed with low maintenance for a period of use of 120 years. This requires that all impacts on the earthworks are known and taken into account accordingly. The most important effects arise from traffic loads, but mass forces from the dead loads of the earth structures, flow forces and climatic effects are also of great importance. Additional effects can result from crossings with other traffic routes as well as with watercourses or media lines.

ERTMS

The ERTMS (European Rail Traffic Management System), the operational control system on the lines of the Trans-European Networks, comprises the following components:

  • Control technology level (TIN – Train Information System)
  • Interlocking technology (INESS – Integrated European Signalling System)
  • Train control (ETCS – European Train Control System)
  • Voice and data communication (GSM-R – Global System for Mobile Communications – Rail(way))

ETCS

Europe's railways suffer from a historically grown variety of very different operational regulations and signalling systems. Since a standardisation is not to be expected in the foreseeable future, the creation of a uniform interface between track and vehicle is pursued as a priority goal for interoperability. This would make cross-border vehicle use possible as a prerequisite for the free network access required by EU directives. The result of the work to date is the European Train Control System (ETCS). The ETCS is part of the operational control system of the European railways ERTMS (European Rail Traffic Management System).

Track

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.

Driving dynamics

Dynamics of vehicle movement are of fundamental importance for railway operations. Driving dynamics include processes that are related to time sequences in the execution of train movements. Above all, the following are to be mentioned:

  • running time calculation (drawing up timetables, investigating whether a given vehicle can keep to a given timetable)
  • the determination of related energy quantities for the comparison of vehicle concepts or for the preparation of an economic efficiency analysis
  • braking distance calculations, e.g. in connection with the planning of signalling systems
  • limit load calculation (determination of the maximum trailer loads that can be driven by a vehicle).

In addition, there are other tasks, such as the determination of additional costs in the event of disrupted operation (so-called operating difficulty costs) or special investigations for the optimisation of vehicle components.

Overhead contact line

The overhead contact line has the task of transmitting the current to the vehicle over a certain distance. The current is picked up via a sliding contact on the current collector (pantograph) and transmitted to the vehicle. To ensure that the contact strip wears evenly, the catenary is laid in a zigzag pattern.

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.

Infrastructure

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 – depending 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.

Slab track

In order to minimise track maintenance, the various types of slab track (FF) were developed, first in England, then in Japan and Italy. In 1972, the German Federal Railways installed the first longer test sections with FF, of which the version installed in a 200 km/h section of the Dortmund–Hanover line at Rheda station, later called "Bauart Rheda", proved its worth.

Four types of construction are distinguished:

  1. compact types
  2. superimposed types
  3. prefabricated systems
  4. others (mass-spring systems, continuously supported systems)

Flank protection

Preventing lateral entry of merging tracks into the train's cleared path.

Geosynthetics

Geosynthetics include 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.

Track

The track is the roadway of track-bound vehicles laid in a ballast bed, consisting of rails, rail supports (usually sleepers) and rail fastening devices.

Track branching

Track branching is the name given to the branching of a track from one (or more) main line track(s), made by means of points, crossings or crossing points.

Track joint

A connection between two tracks consisting of two points and a short piece of track in between is called a track joint.

Track crush

Track compression is a displacement of the tracks due to large internal longitudinal compressive forces caused solely by high temperatures without the influence of any external force. Track buckling is manifested by bulging of the track grating, which is normally much less severe than track warping, but is nevertheless critical to safety.

Twisted track

Twisted track or track warp is a displacement of the tracks due to large internal longitudinal compressive forces caused by external forces or influences (e.g. a lift-off shaft in front of a train). Such track faults can reach lengths of up to 20 m and displace the track grid up to one metre in a horizontal direction.

Head Checks

Head checks are fine surface cracks on the rail head that occur at intervals of 0.5-10 mm and at a 45° angle to the direction of travel and grow towards the inside of the rail. Head checks are caused by rolling contact fatigue due to high wheelset loads and travel speeds.

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 so-called 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.

Superstructure

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 zigzag path, thus it is slid over by a 50 to 75 cm wide area of contact slip surface of the pantograph. 

Formation

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.

Rail

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

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 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.

Sleepers

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 plastic,s 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.

Gauge

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 1,435 mm. In normal operation the dimension of standard gauge railways is permitted to be between 1,430 and 1,470 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.

Subgrade

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.

Sources

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. PMC Media, Leverkusen. ISBN 978-3-7771-0430-0

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