A railroad switch or turnout is a mechanical
installation which enables railway trains to be guided
from one track to another, such as at a railway
Combination of stock rail and tongue rail form a
A set of switches is known as points.
The combination of points and crossing is called a
A turnout generally has a straight "through" track
(such as the main-line) and a diverging route.
Right-hand switches have a diverging path to the
right of the straight track, when coming from the
narrow end, and a left-handed switch has the
diverging track to the left of the straight track.
Here the Rail track A divides into two:-
Track B (the straight track) and Track C (the diverging track)
Various component parts of
They are the main rails of the track to which the tongue
rails are fit closely
They are the outer rail in the turnout.
Tongue rail (Switch rail)
Rails which lie between the 2 stock rails
End portion of the tongue rail is called toe and is connected
by stretcher bar .
It is the moving part of the switch which diverts the train
from one track to the other.
Requirements of tongue rails
• Top and side of the tongue rail is tapered in such a way
that they do not bear any load
• Tongue rail is higher than stock rail by 6mm
• Half thickness of the tongue rail at the toe should be
closely fitted within the stock rail
Used to connect the toe of the tongue rails so that both
the tongues moves through the same distance or gap
Generally 2 or 3 bars are used near and behind the toe
Heel blocks or distance blocks
These are the blocks inserted between the heel of the
stock rail and tongue rail
Used to provide clear gap for the wheel flange.
These are the special plates which are provided for
supporting and sliding the tongue rails.
It is essential because it helps the tongue rail to move
toward and away from stock rails and tongue rails are
able to slide.
They are the rails which are used guide the outer wheel
flange of the train.
To ensure that the train does not derail.
Rails which are used to guide the inner wheel flange of
It is a arrangement of rails introduced at the
junction where two rails cross to permit the wheel
flange of a railway vehicle to pass from one track
to another track.
Important Terms in connection with
Heel clearance / Heel divergence
It is the distance between the running face of the stock rail and
gauge face of the tongue rail measured at the heel of the
Heel clearance according to Indian standards for different
B.G Track:- 13.3cm to 13.7cm
M.G Track :- 11.7cm to 12.1cm
N.G Track:- 9.8cm
It is the distance between the adjacent faces of the
stock rail and the check rail.
It is provided as a clearance for the free movement of
the wheel flange
Flangeway should take into account the amount of
wear. It is observed that upto 6cm flangeway clearance,
wear takes place.
Indian standards for the value of Flangeway clearance
on the basis of wear are:
For 1 in 12 crossing angle, F.C = 6.3cm
For 1 in 8 ½ crossing angle, F.C = 6.6cm
It is the angle between the Running face(Gauge face) of
the stock rail and tongue rail.
For smooth entry and movement of trains, it is
desirable to have small switch angles on tracks used by
fast moving trains.
Throw of Switch
It is the distance through which the toe of the tongue
rail moves sideways to provide desired direction over
Types of Switches
1. Stub switch
First developed for steam railways, was one in
which the straight and diverging tracks were
completely separate and side by side.
The throw of the switch was about 5 inches.
No separate tongue rail was provided.
This type is no more in use and has been replaced
by Split Switch.
2. Split Switch
In this type of switch a tongue rail is combined with
the stock rail.
Split Switches are classified as:
A) On the basis of fixation at heel:
(i) Loose Heel Type
- In this type, tongue rails are joined to lead rails by means of
- Two front bolts are kept loose to allow the throw of the switch
and these bolts are kept tight when the tongue is open
- This is suitable for short length switches.
(ii) Fixed Heel Type (Flexible Type)
- This is an improvement over loose heel type switch.
- In this all the 4 bolts are tight when the tongue is closed
- Gives satisfactory results when long tongue are used
- It is suitable for long tongue rails only.
(i) Under Cut Switches
- In case the height of the stock and tongue rail is
same, it is desirable to cut out a portion of flange
at the foot of the stock rail so that toe of tongue
rail is accommodated under head of the stock
- The disadvantage of this type of switch is that it
becomes weak because flange portion is cut out.
- These switch are generally used in narrow
ii) Over riding Switches:
- In this type separate rail sections of stock rail and
tongue rail are adopted.
- The stock rail of heavy section and tongue rail of light
section are used instead of cutting the flange rather
than weakening the stock rail as in case of undercut
- The tongue rail rides over the flange of the stock rail.
- Generally used in B.G and M.G track.
iii) Straight cut Switches:
- In this type the tongue rail is cut straight in the line with
the stock rail.
- This is done to increase the thickness of toe of the
tongue rail, which increases its strength
- This type of switch is suitable for Bull Headed rails.