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A railway or railroad is a track where the vehicle travels over two parallel steel bars, called rails. The rails support and guide the wheels of the vehicles, which are traditionally either trains or trams. Modern light rail is a relatively new innovation which combines aspects of those two modes of transport. However fundamental differences in the track and wheel design are important, especially where trams or light railways and trains have to share a section of track, as sometimes happens in congested areas.
Both trams and trains have flanged steel wheels with a horizontal section transferring the vehicle weight to the rail and a vertical flange "inboard" to guide the vehicle along the rail using its inside edge.
Rail vehicle wheels are usually mounted on a solid axle, so they turn at the same speed. When a vehicle turns the outer wheel has to travel further than the inner wheel. On a road vehicle, this is usually achieved by allowing the wheels to move independently, and fixing the front wheels in an arrangement known as Ackermann steering geometry.
Trains and trams can turn corners without wheel-slip because the outer horizontal part of the wheels has a slightly tapered rim. The guide flange (ridge) is on the inside to prevent the vehicle from slipping sideways off the rails. The horizontal (cone-shaped) rim makes contact with the slightly convex top of a steel rail in different (horizontal) places so that the outer wheel has a larger effective diameter than the inner wheel.
With both tram and train wheels, this happens naturally because the tires are cone shaped sloping surfaces: the inside diameter is a few millimeters larger than the outside. As the track starts to curve, the train tries to run straight. The wheel flange presses against the side of the curved rail[ citation needed ] so the "contact point" between rail and wheel moves a few millimeters outwards, making the effective diameter of the outer wheel temporarily larger, and equally opposite: the effective diameter of the inner wheel effectively becomes temporarily smaller. This technique works well on large-radius curves which are canted, but not as well on tight curves and railway switches (also known as "points"). This is because the geometry or cant of the track is more difficult to optimize for every possible combination of vehicle and direction of travel.
City trams often use tight curves - sometimes with a radius of much less than about 20 metres (65.6 ft), and canting may be impossible because the surface is shared with road vehicles or pedestrian zones or sidewalks, so the track often has to be flush with the road surface or pavement. In sharp curves, the rail grooves are sometimes made very shallow[ citation needed ], which causes the outer wheel to temporarily ride up onto the edge of its flange. This increases the wheel diameter and the curve can be taken more easily. In extreme cases, the rail has a groove so that the rim of the flange can take most of the weight, the "out-board" tire (on the outer radius of the outer rail) acting as no more than a vertical plate.[ citation needed ]
In contrast, a train wheel is almost never designed to transfer weight through the flange rim, and some train wheels may be damaged if this should happen even once.[ citation needed ]
The point where two straight but intersecting rails cross is called a frog. A groove through each rail allows the wheel flanges to pass through the intersecting rails. Without countermeasures each wheel would dip into the groove and strike the frog point gap causing unacceptable wear. The point where two tracks join and the vehicle can take one of two directions is called a railway switch. This works on the same principle, except that the inner rail is almost continuous and the outer rail has a gap for the flange to pass through.
With a train this problem is solved by using a wide tire. Train rails usually cross at a shallow angle. In the middle of the interchange there is a supporting frog. The tire is guided on each side by guide rails and some portion of the tire always maintains rail contact. This method is not feasible with trams and light railways.[ according to whom? ][ citation needed ]
Tram tires are generally narrower than train tires. Trams use bigger crossing angles and tighter curve radii are more likely than for train tracks. To cope with this difficulty the wheels of trams temporarily transfer the weight of the tram onto the flange to reduce wear on both the frog point and the horizontal surface of the tram wheels. Train wheels are not designed to bear such weight on their flanges.[ according to whom? ][ citation needed ]
A tram wheel which runs on the flange rather than on the horizontal tyre has a larger effective diameter, so the distance travelled per revolution is greater. On the outside track of the curve this is an advantage. It may be necessary to compensate the inner wheel or allow for some slippage. Modern trams and trams tend to have thicker and wider tires which allow for a greater (horizontal) conical section and so greater effective diameter variation and turning ability.
At the junctions of train tracks, the gap in the frog or switch rail is wide. So trams can be accommodated.
The main problem with a train on tram rails is the relatively narrow width of frog and switch gaps and channels of the groove rails designed to accommodate the narrow flanges of tram wheels. The wider flanges of train wheels increase the risk of derailment at these points. On routes where train carriages are driven on tram tracks (as in the past in parts of The Hague), wider grooves are required as a compromise that is practical as wide grooved girder rail is available. [1] [2] [3] A larger structure gauge would also be required This was also done in Los Angeles and in Vancouver as well as elsewhere in North America. The usually or normally limited structure gauge, and tight curves, on tram tracks will also prevent trains from using tram tracks.
In North America the groove would have to be a minimum of 2+1⁄8 in (54 mm) wide and by extension, the maximum distance between the inside faces of the guard flanges of the grooved rails can be no more than 52+1⁄4 in (1,327.1 mm), see below.
Quote:
Design tolerances Design tolerances that affect the lateral displacement of the body include the following:
1. Lateral tolerance between wheels and rails Two types of flanges are permitted on railroad wheels - narrow and wide. The maximum lateral movement T1 possible for a new wheel set centered on in-gage track is a function of the flange type and is determined by the following formula: CAUTION: Use only English units in formulas in this recommended practice
T1 = .5[gt-(gw+2fn)] = .59375” (15.081 mm) for narrow-flange wheels = .375" (9.53 mm) for wide-flange wheels
Where: gt = standard track gage at a point “5/8” (15.9 mm) below top of rail = 56.5" (1,435.1 mm)
gw = minimum gage of wheel set between backs of flanges = 53” (1,346.2 mm)
fn = minimum thickness of new wheel flange = 1.15625” (29.369 mm) for narrow flange or = 1.375" (34.9 mm) for wide flange
Note: The conversions are not in the original text and are for information only.
Quoted from "APTA PR-CS-RP-003-98 Recommended Practice for Developing a Clearance Diagram for Passenger Equipment 5.3.2.1 Design tolerances" (PDF). APTA.com. American Public Transportation Association. 1998-03-26. Archived from the original (PDF) on 2015-06-26. Retrieved 2015-01-17.
Rural and suburban lines can be made compatible for use by several types of vehicles. For example, the narrow gauge railway used by Charleroi Metro in Belgium is ridden by trams, but the tracks are built to train track standards. Trams nonetheless run smoothly on the old NMVB tram net in Anderlues, where shallow groove rails are used[ according to whom? ][ citation needed ]. Between The Hague and Rotterdam, an old railway line was converted for RandstadRail into a route able to carry both the Rotterdam Metro, which uses vehicles built to train standards as well as The Hague trams which uses vehicles built to tram standards. The Electroliners which ran out of Chicago on the Chicago North Shore and Milwaukee Railroad, and afterwards on the Norristown High Speed Line, were another example.
A bogie is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transport. A bogie may remain normally attached or be quickly detachable. It may include a suspension component within it, or be solid and in turn be suspended ; it may be mounted on a swivel, as traditionally on a railway carriage or locomotive, additionally jointed and sprung, or held in place by other means.
A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength ; for easy attachment/transfer of contact force with another object ; or for stabilizing and guiding the movements of a machine or its parts. Flanges are often attached using bolts in the pattern of a bolt circle.
A rubber-tyred metro or rubber-tired metro is a form of rapid transit system that uses a mix of road and rail technology. The vehicles have wheels with rubber tires that run on rolling pads inside guide bars for traction, as well as traditional railway steel wheels with deep flanges on steel tracks for guidance through conventional switches as well as guidance in case a tyre fails. Most rubber-tyred trains are purpose-built and designed for the system on which they operate. Guided buses are sometimes referred to as 'trams on tyres', and compared to rubber-tyred metros.
A railroad switch (AE), turnout, or [set of] points (CE) is a mechanical installation enabling railway trains to be guided from one track to another, such as at a railway junction or where a spur or siding branches off.
A bicycle wheel is a wheel, most commonly a wire wheel, designed for a bicycle. A pair is often called a wheelset, especially in the context of ready built "off the shelf" performance-oriented wheels.
In railway engineering, "gauge" is the transverse distance between the inner surfaces of the heads of two rails, which for the vast majority of railway lines is the number of rails in place. However, it is sometimes necessary for track to carry railway vehicles with wheels matched to two different gauges. Such track is described as dual gauge – achieved either by addition of a third rail, if it will fit, or by two additional rails. Dual-gauge tracks are more expensive to configure with signals and sidings, and to maintain, than two separate single-gauge tracks. It is therefore usual to build dual-gauge or other multi-gauge tracks only when necessitated by lack of space or when tracks of two different gauges meet in marshalling yards or passenger stations. Dual-gauge tracks are by far the most common configuration, but triple-gauge tracks have been built in some situations.
In rail transport, a derailment is a type of train wreck that occurs when a rail vehicle such as a train comes off its rails. Although many derailments are minor, all result in temporary disruption of the proper operation of the railway system and they are a potentially serious hazard.
The Meigs Elevated Railway was an experimental but unsuccessful 19th century elevated steam-powered urban rapid transit system, often described as a monorail but technically pre-electric third rail. It was invented in the US by Josiah Vincent Meigs, of Lowell, Massachusetts, and was demonstrated from 1886 to 1894 in a suburb of Boston called East Cambridge.
An adhesion railway relies on adhesion traction to move the train, and is the most widespread and common type of railway in the world. Adhesion traction is the friction between the drive wheels and the steel rail. Since the vast majority of railways are adhesion railways, the term adhesion railway is used only when it is necessary to distinguish adhesion railways from railways moved by other means, such as by a stationary engine pulling on a cable attached to the cars or by railways that are moved by a pinion meshing with a rack.
The rim is the "outer edge of a wheel, holding the tire". It makes up the outer circular design of the wheel on which the inside edge of the tire is mounted on vehicles such as automobiles. For example, on a bicycle wheel the rim is a large hoop attached to the outer ends of the spokes of the wheel that holds the tire and tube. In cross-section, the rim is deep in the center and shallow at the outer edges, thus forming a "U" shape that supports the bead of the tire casing.
Tramway track is used on tramways or light rail operations. Grooved rails are often used to provide a protective flangeway in the trackwork in city streets. Like standard rail tracks, tram tracks consist of two parallel steel rails.
Tramways are lightly laid industrial railways, often not intended to be permanent. Originally, rolling stock could be pushed by humans, pulled by animals, cable-hauled by a stationary engine, or pulled by small, light locomotives. Tramways can exist in many forms; sometimes simply tracks temporarily placed on the ground to transport materials around a factory, mine or quarry. Many use narrow-gauge railway technology, but because tramway infrastructure is not intended to support the weight of vehicles used on railways of wider track gauge, the infrastructure can be built using less substantial materials, enabling considerable cost savings.
A wheelset is a pair of railroad vehicle wheels mounted rigidly on an axle such that both wheels rotate in unison. Wheelsets are often mounted in a bogie – a pivoted frame assembly holding at least two wheelsets – at each end of the vehicle. Most modern freight cars and passenger cars have bogies each with two wheelsets, but three wheelsets are used in bogies of freight cars that carry heavy loads, and three-wheelset bogies are under some passenger cars. Four-wheeled goods wagons that were once near-universal in Europe and Great Britain and their colonies have only two wheelsets; in recent decades such vehicles have become less common as trainloads have become heavier.
The rail profile is the cross sectional shape of a railway rail, perpendicular to its length.
The Ewing System is a balancing monorail system developed in the late 19th century by British inventor W. J. Ewing. It is not to be confused with the much later system patented by Robert W. Ewing.
The minimum railway curve radius is the shortest allowable design radius for the centerline of railway tracks under a particular set of conditions. It has an important bearing on construction costs and operating costs and, in combination with superelevation in the case of train tracks, determines the maximum safe speed of a curve. The minimum radius of a curve is one parameter in the design of railway vehicles as well as trams; monorails and automated guideways are also subject to a minimum radius.
Baulk road is the name given to a type of railway track or 'rail road' that is formed using rails carried on continuous timber bearings, as opposed to the more familiar 'cross-sleeper' track that uses closely spaced sleepers or ties to give intermittent support to stronger rails.
Track geometry is concerned with the properties and relations of points, lines, curves, and surfaces in the three-dimensional positioning of railroad track. The term is also applied to measurements used in design, construction and maintenance of track. Track geometry involves standards, speed limits and other regulations in the areas of track gauge, alignment, elevation, curvature and track surface. Standards are usually separately expressed for horizontal and vertical layouts although track geometry is three-dimensional.
A train wheel or rail wheel is a type of wheel specially designed for use on railway tracks. The wheel acts as a rolling component, typically press fitted onto an axle and mounted directly on a railway carriage or locomotive, or indirectly on a bogie, also called a truck. The powered wheels under the locomotive are called driving wheels. Wheels are initially cast or forged and then heat-treated to have a specific hardness. New wheels are machined using a lathe to a standardized shape, called a profile, before being installed onto an axle. All wheel profiles are regularly checked to ensure proper interaction between the wheel and the rail. Incorrectly profiled wheels and worn wheels can increase rolling resistance, reduce energy efficiency and may even cause a derailment. The International Union of Railways has defined a standard wheel diameter of 920 mm (36 in), although smaller sizes are used in some rapid transit railway systems and on ro-ro carriages.
The cant of a railway track or camber of a road is the rate of change in elevation (height) between the two rails or edges of the road. This is normally greater where the railway or road is curved; raising the outer rail or the outer edge of the road creates a banked turn, thus allowing vehicles to travel round the curve at greater speeds than would be possible if the surface were level.