The gauge of a railway track is defined as the
clear minimum perpendicular distance between
the inner faces of the two rails.
Following are the factors affecting the choice of a
1. Traffic Condition:
If the intensity of traffic on the track is likely to be
more, a gauge wider than the standard gauge is
2. Development of Poor Areas:
The narrow gauges are laid in certain parts of the
world to develop a poor area and thus link the
poor area with the outside developed world.
4. Speed of Movement:
The speed of a train is a function of the diameter
of wheel which in turn is limited by the gauge.
The wheel diameter is usually about 0.75 times
the gauge width and thus, the speed of a train is
almost proportional to the gauge.
If higher speeds are to be attained, the B.G track
is preferred to the M.G or N.G track.
3. Cost of Track:
The cost of railway track is directly proportional
to the width of its gauge.
If the fund available is not sufficient to construct
a standard gauge, a metre gauge or a narrow
gauge is preferred rather than to have no
railways at all.
5. Nature of Country:
In mountainous country, it is advisable to have a
narrow gauge of the track since it is more
flexible and can be laid to a smaller radius on
This is the main reason why some important
railways, covering thousands of kilometers, are
laid with a gauge as narrow as 610 mm.
The different gauges can broadly be divided into
the following four categories:
1) Broad Gauge:
width 1676 mm to 1524 mm or 5’6” to 5’0”
2) Standard Gauge:
width 1435 mm and 1451 mm or 4’-8⅟2”
3) Metre Gauge:
width 1067 mm, 1000 mm and 915 mm or 3’-6”,
3’-33/8” and 3’-0”
4) Narrow Gauge:
width 762 mm and 610 mm or 2’-6” and 2’-0”. 7
The high carbon rolled steel sections, which are
laid end-to-end, in two parallel lines over sleepers
to provide continuous and leveled surface for the
trains to move and for carrying axle loads of the
rolling stock are called rails.
Functions of the rails:
To provide continuous and level surface for the
movement of trains with minimum friction with
steel wheels of the rolling stock;
Provide strength, durability and lateral guidance
to the track;
Transmit the axle loads to sleepers which transfer
the same load to the underlying ballast and
Bear the stresses developed due to heavy vertical
loads, breaking forces and temperature variance.9
1. Double Headed Rails:
This type of rail consists of three parts – upper
table, web, and lower table;
Both the upper and lower tables were identical;
They were introduced with the hope of doubling
the life of rails;
When the upper table was worn out, the rails can
be reversed in the chair and thus, the lower table
can be brought into use;
However, this idea soon turned out to be wrong
because it was observed that long contact with
chairs made the surface of lower table very rough
and smooth running of trains was then
Thus, these rails are nowadays practically out of
2. Bull Headed Rails:
These rails consist of head, web and foot and are
made of steel;
The head is larger than the foot and the foot is
designed only to properly hold the wooden keys
with which the rails are secured to chairs;
The two cast-iron chairs are required per each
sleeper when these rails are adopted.
These rails are extensively used in England and in
some parts of Europe.
3. Flat-footed Rails:
In this type of rail, the foot is spread out to form a
This form of rail was invented by Charles Vignoles
in 1836 and hence, these rails are sometimes
known as Vignoles rails;
At present, about 90% of the railway track in the
world is laid with this form of rails.
i. Chairs: No chairs are required in this form of
rails. The foot of the rail is directly spiked to the
sleepers. This fact makes them economical.
ii. Stiffness: This form of rail is stiffer, both
vertically and laterally than the bull-headed rail
of equal weight. Especially on curves, the lateral
stiffness of rails is very important.
iii. Kinks: This form of rail is less liable to develop
kinks and it maintains a more regular top surface
than the bull-headed rails.
iv. Cost: The flat footed rails are found to be
cheaper than the bull-headed rails.
v. Load Distribution: The flat footed rail distributes
the train load over a great number of sleepers.
This results in greater track stability.