A
railway
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in Track (rail transport), tracks. In contrast to road transport, where the ...
or
railroad
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
is a
track where the vehicle travels over two
parallel
Parallel is a geometric term of location which may refer to:
Computing
* Parallel algorithm
* Parallel computing
* Parallel metaheuristic
* Parallel (software), a UNIX utility for running programs in parallel
* Parallel Sysplex, a cluster of I ...
steel bars, called
rails
Rail or rails may refer to:
Rail transport
*Rail transport and related matters
* Rail (rail transport) or railway lines, the running surface of a railway
Arts and media Film
* ''Rails'' (film), a 1929 Italian film by Mario Camerini
* ''Rail'' ...
. The rails support and guide the wheels of the vehicles, which are traditionally either
train
In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often k ...
s or
tram
A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport ...
s. 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.
Terminology

Both trams and trains have
flange
A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...
d steel
wheel
A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be ...
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 vehicle
The term rolling stock in the rail transport industry refers to railway vehicles, including both powered and unpowered vehicles: for example, locomotives, freight and passenger cars (or coaches), and non-revenue cars. Passenger vehicles can b ...
wheels are usually mounted on a solid
axle
An axle or axletree 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 the vehicle, with the wheels rotating around the axle. In the former case, beari ...
, 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
The 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 radii.
It ...
.
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
A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...
(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
Convex or convexity may refer to:
Science and technology
* Convex lens, in optics
Mathematics
* Convex set, containing the whole line segment that joins points
** Convex polygon, a polygon which encloses a convex set of points
** Convex polytop ...
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 so the "contact point" between rail and wheel moves a few
millimeter
file:EM Spectrum Properties edit.svg, 330px, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter.
The millimetre (American and British Eng ...
s 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
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type ...
(also known as "points"). This is because the
geometry
Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
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
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
of much less than about , and canting may be impossible because the surface is shared with road vehicles or
pedestrian zones or
sidewalk
A sidewalk (North American English), pavement (British English), footpath in Australia, India, New Zealand and Ireland, or footway, is a path along the side of a street, highway, terminals. Usually constructed of concrete, pavers, brick, stone ...
s, so the track often has to be flush with the
road surface
A road surface (British English), or pavement (American English), is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, hoggin, cob ...
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, 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.
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.
Track junctions
The point where two straight but intersecting rails cross is called a
frog
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" '' Triadobatrachus'' is ...
. 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
A railroad switch (), turnout, or ''set ofpoints () 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.
The most common type ...
. 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
Rail or rails may refer to:
Rail transport
*Rail transport and related matters
* Rail (rail transport) or railway lines, the running surface of a railway
Arts and media Film
* ''Rails'' (film), a 1929 Italian film by Mario Camerini
* ''Rail'' ...
usually cross at a shallow
angle
In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the '' vertex'' of the angle.
Angles formed by two rays lie in the plane that contains the rays. Angles ...
. 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.
Tram tires are generally narrower than train tires. Trams use bigger crossing angles and tighter
curve radii
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also th ...
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.
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.
Interoperability problems
At the
junctions
Junction may refer to:
Arts and entertainment
* ''Junction'' (film), a 2012 American film
* Jjunction, a 2002 Indian film
* Junction (album), a 1976 album by Andrew Cyrille
* Junction (EP), by Basement Jaxx, 2002
* Junction (manga), or ''Hot ...
of
train tracks, the gap in the frog or switch rail is wide. So
tram
A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport ...
s 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
The Hague ( ; nl, Den Haag or ) is a list of cities in the Netherlands by province, city and municipalities of the Netherlands, municipality of the Netherlands, situated on the west coast facing the North Sea. The Hague is the country's ad ...
), wider grooves are required as a compromise that is practical as wide grooved
girder rail is available.
MRT Track & Services Co., Inc / Krupp, T and girder rails, scroll down.
/ref> A larger structure gauge
A structure gauge, also called the minimum clearance outline, is a diagram or physical structure that sets limits to the extent that bridges, tunnels and other infrastructure can encroach on rail vehicles. It specifies the height and width of pl ...
would also be required This was also done in Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the wor ...
and in Vancouver
Vancouver ( ) is a major city in western Canada, located in the Lower Mainland region of British Columbia. As the most populous city in the province, the 2021 Canadian census recorded 662,248 people in the city, up from 631,486 in 2016. Th ...
as well as elsewhere in North America. The usually or normally limited structure gauge, and tight curves, on tram tracks will also prevent train
In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often k ...
s from using tram tracks.
In North America the groove would have to be a minimum of wide and by extension, the maximum distance between the inside faces of the guard flanges of the grooved rails can be no more than , 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 t-(gw+2fn) = .59375” () for narrow-flange wheels
= .375" () for wide-flange wheels
Where: gt = standard track gage at a point “5/8” () below top of rail = 56.5" ()
gw = minimum gage of wheel set between backs of flanges = 53” ()
fn = minimum thickness of new wheel flange = 1.15625” () for narrow flange or = 1.375" () for wide flange
Note: The conversions are not in the original text and are for information only.
Quoted from
Mixed vehicle rail design
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
Charleroi Metro (french: Métro de Charleroi; previously known as the ''Charleroi Premetro'' (french: Métro léger de Charleroi)) is a light rail network in Belgium, consisting of a loop line around central Charleroi and three branches towards ...
in Belgium
Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to ...
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
Anderlues (; wa, Anderluwe; pcd, Andérluve) is a municipality of Wallonia located in the province of Hainaut, Belgium.
On 1 January 2006 Anderlues had a total population of 11,578. The total area is which gives a population density of 680 inh ...
, where shallow groove rails are used. Between The Hague and Rotterdam
Rotterdam ( , , , lit. ''The Dam on the River Rotte'') is the second largest city and municipality in the Netherlands. It is in the province of South Holland, part of the North Sea mouth of the Rhine–Meuse–Scheldt delta, via the ''"N ...
, an old railway line was converted for RandstadRail
RandstadRail () is a light rail network in the Rotterdam–The Hague metropolitan area in the west of the Netherlands that is jointly operated by HTM Personenvervoer (HTM) and Rotterdamse Elektrische Tram (RET). It connects the cities of Rot ...
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 Electroliner
The Electroliners are a pair of streamlined interurban trainsets built by the St. Louis Car Company in 1941. Initially numbered 801–802 and 803–804, they were operated by the Chicago North Shore and Milwaukee Railroad from 1941 to 1963, fol ...
s which ran out of Chicago
(''City in a Garden''); I Will
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, map_caption = Interactive Map of Chicago
, coordinates =
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, subdivision_type = List of sovereign states, Count ...
on the Chicago North Shore and Milwaukee Railroad
The Chicago North Shore and Milwaukee Railroad (reporting mark CNSM), also known as the North Shore Line, was an interurban railroad that operated passenger and freight service over an route between the Chicago Loop and downtown Milwaukee, as ...
, and afterwards on the Norristown High Speed Line
The Norristown High Speed Line (NHSL), also called the Purple Line, the P&W, or Route 100,) is a interurban light rapid transit line operated by SEPTA, running between the 69th Street Transportation Center in Upper Darby and the Norristown Tr ...
, were another example.
See also
* Jacobs bogie
Jacobs bogies (named after Wilhelm Jakobs,, 1858–1942, a German mechanical railway engineer) are a type of rail vehicle bogie commonly found on articulated railcars and tramway vehicles.
Instead of being underneath a piece of rolling stock ...
* Grooved rail
* Minimum railway curve radius
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 ...
* Rail tracks
A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleepe ...
* Tramway track
Tramway track is used on tramways or light rail operations. Grooved rails (or girder 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 ...
* Wheel gauge
* Wheelset
References
External links
Wirth Girder Rail
MRT Track & Services Co., Inc / Krupp, T and girder rails, scroll down.
The Electric Interurban Railways in America
accessdate = 10 June 2014
Trampower LR55 rail
{{DEFAULTSORT:Train and tram track comparison
Permanent way
Technological comparisons