Difference between train and tram rails
Encyclopedia
A railroad or railway 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 train
s and tram
s. Modern light rail
is a relatively new innovation which combines aspects of those two modes of transport. However there are some fundamental design differences in the track and wheel design which are important, especially where trams or light railways and trains have to share a section of track, as sometimes happens in congested towns.
Both trams and trains have flange
d iron wheel
s 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.
wheels are usually mounted on a solid axle
, so they turn at the same speed. When a vehicle turns a corner, 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 prevents the rail 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 that on the outside. As the track starts to curve, the train will initially try to run straight on. The wheel flange presses against the side of the curved rail So the "contact point" between rail and wheel will move a few millimeters outwards, making the effective diameter of the outer wheel temporarily larger, and equally opposite: the effective diameter of the inner wheel will effectively become temporarily smaller. This technique works well on large-radius curves which are canted
, but not so well on tight curves and railway Railroad switch
es (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 - often with a radius of less than about 20 meters (roughly 65 ft), and canting may impossible because the surface is shared with road vehicles or pedestrian zones or sidewalk
s, so the track often has to be level with the road surface or pavement. In sharp curves, the rail grooves are sometimes made very shallow, 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, it may even be that the rail has a groove so that the rim of the flange can take most of the weight, the "out-board" tyre (on the outer radius of the outer rail) being reduced to effectively no more than a vertical iron plate.
In contrast, a train wheel is almost never designed to transfer weight through the flange rim, and some tires may be damaged if this should happen even once.
With a train this problem is solved by using a wide tire. Train rails cross at a shallow angle
. In the middle of the interchange there is a supporting frog, where the tire is guided on each side by guide rails, some portion of the tire always maintains rail contact. This method is not feasible with trams and light railways.
Tram tires are generally narrower than train tires. additionally steeper crossing angles and tighter curve radius is more likely than for tracks designed for solely trains. To cope with this difficulty the wheels of trams can temporarily transfers all the weight of the tram onto the flange to reduces wear on both the frog point or rail-gap and the horizontal surface of the tram wheels. Train wheels are not designed to bear such weight on their flanges.
A tram wheel wheel which runs on the flange rather on the horizontal tyre has a larger effective diameter, so the distance travelled per revolution is greater. On the track on the outside of the curve this is an advantage, it may be necessary to compensate the inner wheel or allow for some slippage. Modern trams and tram
s tend to have thicker and wider tires which allows for a greater (horizontal) conical section and so greater effective diameter variation and turning ability.
, tram
, or tram-train
equipment, using tram rails in city center, and on interurban sections of train railroads now have interoperable flanges combined with wide tires.
tram net in Anderlues
, where shallow groove rails are used. Between The Hague and Rotterdam, an old railway line has been converted for RandstadRail
into a route able to carry both the Rotterdam Metro
which uses train technology as well as The Hague tram
technology vehicles.
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...
steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
bars
I-beam
-beams, also known as H-beams, W-beams , rolled steel joist , or double-T are beams with an - or H-shaped cross-section. The horizontal elements of the "" are flanges, while the vertical element is the web...
, called rails
Rail profile
The rail profile is the cross sectional shape of a railway rail, perpendicular to the length of the rail.In all but very early cast iron rails, a rail is hot rolled steel of a specific cross sectional profile designed for use as the fundamental component of railway track.Unlike some other uses of...
. The rails support and guide the wheels of the vehicles, which are traditionally either train
Train
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...
s and tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...
s. Modern light rail
Light rail
Light rail or light rail transit is a form of urban rail public transportation that generally has a lower capacity and lower speed than heavy rail and metro systems, but higher capacity and higher speed than traditional street-running tram systems...
is a relatively new innovation which combines aspects of those two modes of transport. However there are some fundamental design differences in the track and wheel design which are important, especially where trams or light railways and trains have to share a section of track, as sometimes happens in congested towns.
Terminology
Flange
A flange is an external or internal ridge, or rim , for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera; or for a flange of a rail car or tram wheel...
d iron wheel
Wheel
A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...
s 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.
Difference in Technique in Curves
Rail vehicleTram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...
wheels are usually mounted on a solid axle
Axle
An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle...
, so they turn at the same speed. When a vehicle turns a corner, 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
Ackermann steering geometry
Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radius...
.
Trains and trams can turn corners without wheel-slip because the outer horizontal part of the wheels has a slightly tapered
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
rim. The guide flange
Flange
A flange is an external or internal ridge, or rim , for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera; or for a flange of a rail car or tram wheel...
(ridge) is on the inside to prevents the rail vehicle from slipping sideways off the rails. The horizontal (cone shaped) rim makes contact with the slightly convex top of a steel rail
Rail profile
The rail profile is the cross sectional shape of a railway rail, perpendicular to the length of the rail.In all but very early cast iron rails, a rail is hot rolled steel of a specific cross sectional profile designed for use as the fundamental component of railway track.Unlike some other uses of...
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 that on the outside. As the track starts to curve, the train will initially try to run straight on. The wheel flange presses against the side of the curved rail So the "contact point" between rail and wheel will move a few millimeters outwards, making the effective diameter of the outer wheel temporarily larger, and equally opposite: the effective diameter of the inner wheel will effectively become temporarily smaller. This technique works well on large-radius curves which are canted
Cant (road/rail)
The cant of a railway track or a road is the difference in elevation between the two edges...
, but not so well on tight curves and railway Railroad switch
Railroad switch
A railroad switch, turnout or [set of] points is a mechanical installation enabling railway trains to be guided from one track to another at a railway junction....
es (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 - often with a radius of less than about 20 meters (roughly 65 ft), and canting may impossible because the surface is shared with road vehicles or pedestrian zones or sidewalk
Sidewalk
A sidewalk, or pavement, footpath, footway, and sometimes platform, is a path along the side of a road. A sidewalk may accommodate moderate changes in grade and is normally separated from the vehicular section by a curb...
s, so the track often has to be level with the road surface or pavement. In sharp curves, the rail grooves are sometimes made very shallow, 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, it may even be that the rail has a groove so that the rim of the flange can take most of the weight, the "out-board" tyre (on the outer radius of the outer rail) being reduced to effectively no more than a vertical iron plate.
In contrast, a train wheel is almost never designed to transfer weight through the flange rim, and some tires may be damaged if this should happen even once.
Track Junctions
The point where two straight but intersecting railroads cross is called a frog. A groove through each rail allows the wheel flanges to pass through the intersecting rails, and without countermeasures each wheel would dip into the groove and strike the frog point gap causing excessive wear. Where two tracks join and the vehicle can be directed in one of two directions is called a railway switch which works on the same principle, except 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 cross at a shallow angle
Angle
In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...
. In the middle of the interchange there is a supporting frog, where the tire is guided on each side by guide rails, some portion of the tire always maintains rail contact. This method is not feasible with trams and light railways.
Tram tires are generally narrower than train tires. additionally steeper crossing angles and tighter curve radius is more likely than for tracks designed for solely trains. To cope with this difficulty the wheels of trams can temporarily transfers all the weight of the tram onto the flange to reduces wear on both the frog point or rail-gap and the horizontal surface of the tram wheels. Train wheels are not designed to bear such weight on their flanges.
A tram wheel wheel which runs on the flange rather on the horizontal tyre has a larger effective diameter, so the distance travelled per revolution is greater. On the track on the outside of the curve this is an advantage, it may be necessary to compensate the inner wheel or allow for some slippage. Modern trams and tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...
s tend to have thicker and wider tires which allows for a greater (horizontal) conical section and so greater effective diameter variation and turning ability.
Interoperability Problems
There is a significant difference between relatively light tram rails and full-scale train rails designed to carry heavy loads. At train junctions, the gap in the frog or switch rail is large and deep. Because train wheels are larger and the flanges do not have to carry vertical loads, they can be designed to cope with gaps in the rail which might defeat the smaller tram-wheels.Tram on Train Tracks
Given the above concerns, in particular the difficulty ti introduce a surface to allow the tram flange to take the weight of the vehicle, a tram with traditional wheels can not drive on train rails without "falling into the gap" designed for the flanges of vehicles on the crossing line.. Modern light railLight rail
Light rail or light rail transit is a form of urban rail public transportation that generally has a lower capacity and lower speed than heavy rail and metro systems, but higher capacity and higher speed than traditional street-running tram systems...
, tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...
, or tram-train
Tram-train
A tram-train is a light-rail public transport system where trams run both on an urban tramway network and on main-line railways to combine the tram's flexibility and availability and the train's greater speed...
equipment, using tram rails in city center, and on interurban sections of train railroads now have interoperable flanges combined with wide tires.
Train on Tram Tracks
The main problem with a train on tram rails are the relatively small dimensions of frog and switch gaps and channels designed to accommodate the flanges of vehicles on the crossing line. The larger dimensions of train wheels increases the risk of derailment at these points. On routes where train carriages are driven over on tram tracks (as in the past in The Hague), wider and deeper grooves are required as a compromise that practical but not optimal, requiring greater care and lower speeds for both types of vehicle.Mixed vehicle rail design
Many modern rural and suburban lines are compatible for use by several different types of vehicles. For example, the Narrow gauge railway used by Charleroi Metro are ridden by trams, but the tracks are built with train technology which does not permit the vertical load to be borne by the flange. The trams nonetheless run smoothly on the old NMVBVicinal tramway
The Tramways vicinaux or Buurtspoorwegen were a system of narrow gauge tramways or local railways in Belgium, which covered the whole country and had a greater route length than the mainline railway system...
tram net in Anderlues
Anderlues
Anderlues is a Walloon municipality located in the Belgian province of Hainaut. On January 1, 2006 Anderlues had a total population of 11,578. The total area is 17.02 km² which gives a population density of 680 inhabitants per km². Its postcode is 6150....
, where shallow groove rails are used. Between The Hague and Rotterdam, an old railway line has been converted for RandstadRail
RandstadRail
RandstadRail network in the southern part of the Randstad conurbation in the west of the Netherlands, connecting The Hague, Zoetermeer and Rotterdam, consists of a metro-like line between The Hague and Rotterdam and two light rail lines between The Hague and Zoetermeer...
into a route able to carry both the Rotterdam Metro
Rotterdam Metro
The Rotterdam Metro is a rapid transit system operated in Rotterdam and surrounding municipalities by RET. The first line, called Noord - Zuidlijn opened in 1968 and ran from Centraal Station to Zuidplein, crossing the river Nieuwe Maas in a tunnel. It was the first metro system to open in the...
which uses train technology as well as The Hague tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...
technology vehicles.
See also
- Grooved rail
- Minimum railway curve radiusMinimum railway curve radiusThe minimum railway curve radius, the shortest design radius, has an important bearing on constructions costs and operating costs and, in combination with superelevation in the case of train tracks, determines the maximum safe speed of a curve. Superelevation is not a factor on tramway tracks...
- Rail tracks
- Tramway trackTramway trackTramway track is used on tramways or light rail operations. Grooved rails are often used in order to make street running feasible...
- Wheelset