INTRODUCTION
Rails are rolled steel sections laid along two parallel lines over sleepers. Rails are can be considered as steel girders carrying axle loads. Rails are made of high carbon steel to withstand wear and tear. They should also be strong enough to bear the load and impacts which may come over them. Rails should be constructed in such a way that every portion can be easily maintained, repaired and replaced if required at any stage.
FUNCTIONS OF RAILS
Rails in the railway track should serve the following functions:
1. To provide a smooth pathway to trains. This pathway has a very less friction.
2. To transfer the wheel loads to the sleepers, ballast and the formation between them and the safe limits.
3. To bear the vertical and lateral forces of the trains moving at high speeds.
4. To bear the thermal stresses due to change in temperature as well as braking forces caused while stopping the trains at railway stations.
5. To have minimum wear to avoid replacement charges and failure of rails due to wear.
REQUIREMENTS OF RAILS
They should meet the following requirements to serve intended purposes:
1) They should be of proper composition of steel.
2) The rail should possess adequate lateral stiffness and vertical stiffness.
3) Rails should be capable of withstanding lateral forces.
4) The thickness of web of rail should be sufficient to take safely the load coming on the rail.
5) The width of foot of rail should be sufficient to grant stability against overturning and it should be capable of spreading the load on a large area of the sleeper.
6) The shape of the bottom of the head and top of the foot should be such that the fish plate could be fixed easily. 
7) There should be a balanced distribution of metal in head, web and foot of rail so that each of them is able to fulfill its assigned function.
8) The height of the rail should be adequate so that rail has sufficient vertical stiffness and 
strength as a beam.
9) The fillet radii must be large to reduce the concentration of stresses.
10) The tensile strength of the rail material should not be less than 72 kg/mm2.
RAIL SECTIONS
Rail sections are classified as:
1. Double headed rails or Dump-bell rails
2. Bull headed rails
3. Flat footed rails
1) Double headed rails
These rails were provided at the first stage of development. It consists of three parts i.e., lower table, web and upper table. The upper and lower tables are identical. These were kept same with the idea of increasing the life of the rails. The idea was that when the upper table had worn out due to the impact of moving wheels, it could be inverted and re-used with lower section at the top. But later on it was established that under the impact of the wheels, the lower table become dented and could not be re-used for smooth riding. The rail section was, therefore, re-used. D.H. rails are therefore, practically out of use on Indian Railways.
2) Bull headed Rails
Bulls Headed Rails consist of head, web and foot, these rails made of steel. The head is larger than the foot. In this rail the metal in the foot is sufficient to bear the stresses caused by moving wheels. In the bull headed rails, bottom portion was designed by only to properly hold the wooden keys with which the rails are fitted to chairs. B.H. rails are in held in position by means of chairs fixed to sleepers.
The merits and demerits of B.H. rails are given below.
Merits
a) These rails have long life.
b) These rails Maintain better alignment.
c) These rails facilitate easy construction of points and crossings required for changing the track of the train, while it approaches or leaves the stations.
d) These rails provide greater stability to the track.
e) These rails can be removed and replaced easily.
Demerits
A. These rails are not stronger in every direction.
B. These rails require costly fastenings.
C. These rails are costly.
D. These rails require more attention and maintenance.
3) Flat footed rails 
These rails are mostly used on Indian Railways due to its more lateral stability. About 90 percent of the railway track in the world is laid with these rails due to the following advantages :These rails were invented by Charles Vignole in 1836 at the same time when B.H. rail was 
designed. Therefore, these are also known as Vignole's rails. In this case, the bottom section is spread out to form a base. The idea behind invention was that this rail can be directly used 
on sleepers with few fastenings. When these are directly laid on wooden sleepers, it was 
found that heavy train loads sunk the rails in the sleepers thus loosening the spikes. To avoid this tendency, steel bearing plates are used between sleepers and rails. 
a) These do not require any chairs. The foot of the rail is spiked directly to the sleepers. This fact 
makes these chairs economical. 
b) These are stiffer both vertically and laterally than B.H. rails of equal weight.
c) These are less liable to develop kinks.
d) These are cheaper than B .H. rails.
e) These distribute load over greater number of sleepers.
f) These provide greater track stability.
g) These tend to increase the life of sleepers and rails.
h) These tend to reduce the maintenance costs.
i) These cause less rail failures and disruptions to the traffic movements.
Flat Footed rails have also some of the disadvantages as given below :
i. These cannot be easily maintained.
ii. F.F. rails, cannot be easily and therefore repairs become difficult.
iii. These cannot be used at points and crossings to divert the train from one track to another.
iv. These sunk in the sleepers under the effect of heavy train loads.
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