The document provides a comprehensive overview of railway engineering, focusing on the definitions, purposes, types, and classifications of railway stations and yards. It details different station types such as wayside, junction, and terminal stations, as well as various yard types like passenger yards, goods yards, and marshalling yards. Additionally, it describes essential railway equipment and facilities needed for effective operation and maintenance of railway systems.

1. PREPARED BY
M.SHANMUGARAJ
LECTURER / CIVIL
V.S.V.N.POLYTECHNIC COLLEGE
VIRUDHUNAGAR
UNIT-IV RAILWAY ENGINEERING

2. Station and Yards
Definition of Station
Arailway station or arailroad station and often shortened to juststation, is a railwayfacility wheretrainsregularly stop to load or unloadpassengersand/orfreight

3. Station and Yards

4. Purpose of Railway station
For exchange of passengers and goods.
For control of train movements
To enable the trains on a single line track to cross from opposite directions.
To enable the following express trains to overtake
For taking diesel or coal and water for locomotives
For detaching engines and running staff
For detaching or attaching of compartments and wagons
For sorting of bogies to form new trains, housing of locomotive in loco sheds.
In emergencies in ease of dislocation of track due to rains, accidents etc...
For repairing engines and changing their direction
Railway station are having suitable approach roads from surrounding areas.

5. Types of Stations
Wayside Stations, Junction Stations, Terminal Stations

6. Wayside Stations
In this type arrangements are made for crossing or for overtaking trains. Wayside stations are of the following types.
i.Haltstations, ii.FlagStations, iii.Crossingstations

7. Halt Stations
Ahalt, is a small station, usually unstaffed and with few or no facilities. In some cases, trains stop only onrequest, when passengers on the platform indicate that they wish to board, or passengers on the train inform the crew that they wish to alight.

8. Halt Stations

9. Flag Stations
Flag stationsdescribes a stopping point at which trains stop only on an as-need or request basis; that is, only if there are passengers to be picked up or dropped off.
These stations have no overtaking or crossing facilities and arrangements to control the movement of trains. These stations have buildings, staff and telegraph facilities.
Some of the flag stations have sidings also in the form of loops.

10. Flag Stations

11. Crossing Stations
Provided with facilities for crossing
In this type at least one loop line is provided to allow another train if one track is already occupied by a waiting train
Generally the train to be stopped is taken on the loop line and the through train is allowed to pass on the main line

12. Crossing Stations

13. Junction stations:
At a junction stations, lines from three or more directions meet
The stations where a branch line meets the main line are known as junctions.
Arrangements in junction stations
Facilities for interchange of traffic between main and branch line
Facilities to clean and repair the compartments of the trains
Facilities for good sidings, engine sheds, turn table etc.

14. Junction stations:

15. Terminal Stations:
It is a station where a railway line or one of its branches terminates
Facilities required in terminal stations
Watering, coaling, cleaning, servicing the engine
Turn table for the change of direction of the engine
Facilities for dealing goods traffic. Such as marshalling yard, engine sheds, sidings etc.
In circulating area, ticket office, restaurant etc are provided and it is directly connected to the road

16. Terminal Stations:

17. Classification of Stations
Stations can be classified on the basis of their operation as
1.Block stations-Class A, Class B and Class C
2.Non Block Stations-Class D stations or Flag stations
3.Special class stations.

18. Block Stations:
The stations at the end the block sections are called Block stations
Authority to proceed is given in the shape of token at these stations.
Class A Station:
On these stations the track is cleared up to 400m beyond the home signal for giving permission to approach a train
Class B Station:
In such stations, the other signal is provided at about 580m from the home signal
Class C Station:
On these stations passengers are not booked. It is simply a block meant for splitting a long block section and to reduce the interval between the successive trains.

19. Non Block Stations:
Also known as Class D station or Flag station
Situated between two consecutive block stations
May not be telegraphically connected to the adjacent stations
No equipment or staff is provided for controlling the movements of the trains.
Trains are stopped by flag signals only

20. Special class stations:
Stations not coming under block station and non block stations are called special class station

21. Platforms -Passenger and Goods platforms:
Arailway platformis a section of pathway, alongsiderail tracksat arailway station,metro stationortram stop, at which passengers may board or alight from trains or trams.
Almost all rail stations have some form of platform, with larger stations having multiple platforms.
Platform types include thebay platform,side platform(also calledthrough platform),split platformand theisland platform.
A bay platform is one at which the track terminates, i.e. a dead-end orsiding.
A side platform is the more usual type, alongside tracks where the train arrives from one end and leaves towards the other.
An island platform has through platforms on both sides; it may be indented on one or both ends, with bay platforms.

22. Passenger Platform

23. Goods Platform

24. Definition of Yard:
An area consisting of a network of railway tracks, sidings, and sheds for storing, maintaining, and joining engines and carriages.
A yard is defined as a system of tracks laid within definite limits for various purposes such as receiving sorting and dispatch of vehicles.

25. Railway Yard

26. Types of Yards:
Passenger yards, Goods yards, Marshalling yards, Locomotive yards

27. Passenger yards:
Function of passenger yard is to provide all the facilities for the safe movement of passengers.
Facilities in passenger yards
Booking office, enquiry office, luggage booking room, cloak room and waiting room for passengers
Parking space for vehicles
Signals for reception and dispatch of trains
Platforms and sidings for shunting facilities
Facilities for changing batteries
Facilities for passing a through train
Washing lines, sick lines facilities

28. Passenger yards

29. Goods yards:
Agoods station(also known as agoods yard,goods depotorfreight station) is, in the widest sense, arailway stationwhich is exclusively or predominantly where goods (orfreight) of any description are loaded or unloaded from ships or road vehicles and/or where goods wagons are transferred to local sidings.
These are provided for receiving, loading and unloading of goods

30. Goods yards

31. Requirements of a goods yard
Approach road for movement of goods
Sufficient number of platforms for loading and unloading
Sufficient number of godowns
Booking office
Cart weighing machine
Cranes for loading and unloading
Vacuum testing machine

32. Marshalling yards:
Marshalling yardis arailroadyardfound at somefreight train stations, used to separaterailroad carson to one of several tracks
It is the place where goods wagons received from different centresare sorted out and placed in order to detached at different stations
The marshalling yards are distribution centres
Empty wagons are also kept in marshalling yards

33. Marshalling yards:

34. Factors for the efficient functioning of marshalling yards
Shunting operations should not disturb the regular trains
Should be kept parallel to the running trains
Movement of wagons in one direction only
Repair facilities should be provided on one or more sidings
Connected to all important railway stations
Goods yard should be nearer to the marshalling yard

35. Types of marshalling yards:
(i)Flat yard (ii)Gravity yard (iii)Hump yard

36. Flat yard:
Flat yards are constructed on flat ground, or on a gentle slope. Freight vehicles are pushed by a locomotive and coast to their required location.
Aflat yardhas no hump, and relies on locomotives for all car movements

37. Gravity yard:
The whole yard is set up on a continuous falling gradient and there is less use of shunting engines.
Typical locations of gravity yards are places where it was difficult to build a hump yard due to thetopography
Gravity yards also have a very large capacity but they need more staff than hump yards and thus they are the most uneconomical classification yards.

38. Hump-yard:
These are the largest and most effective classification yards, with the largest shunting capacity—often several thousand cars a day.
The heart of these yards is the hump: a lead track on a hill (hump) that an engine pushes the cars over.
Single cars, or some coupled cars in a block, are uncoupled just before or at the crest of the hump, and roll by gravity onto their destination tracks
Ahump yardhas a constructed hill, over which freight cars are shoved by yard locomotives, and then gravity is used to propel the cars to various sorting tracks

39. Hump-yard:

40. Locomotive yards:
This is the yard which houses the locomotives for various facilities such as watering, fueling, cleaning, repairing, servicing etc.

41. Locomotive yards:

42. Locomotive yards:

43. Requirements of a locomotive yard
Should be located near the passenger and goods yards
Water column
Engine shed, Ash pit, inspection pit, repair shed, turn table
Hydraulic jack for lifting operations
Over head tank and loco well
Sick siding
Place for future expansion

44. Level crossings
Alevel crossing(a primarily British term; usually known as arailroad crossingin the United States) is an intersection where arailway linecrosses aroadorpathat the same level
Other names includerailway crossing,grade crossing,road through railroad, andtrain crossing.
The type of facilities provided at level crossing depends up on the following
Nature of the road
Nature of the traffic on road
Number of trains passing over the level crossing

45. Level crossings

46. Classification of level crossing:
Special class –Traffic is exceptionally heavy
A class –On grand trunk roads
B class –Metelledroads
C class –unmetelledroads
D class –used for cattle‘s as ramps and pedestrians only

47. Station Equipments
For efficient running of trains, safety of traffic, repairing, cleaning, examining of locomotives etc. some equipments and machinery is needed. These equipments are known as station equipment

48. Engine sheds:
Railway engine sheds were provided at terminal stations, junctions, and other locations around the railway.
They provided covered accommodation for servicing locomotives -this could be simple tasks such as changing brake blocks to more complex task that involved dismantling and repairing the engine.
Types of engine sheds are (i) Rectangular type (ii) Circular type

49. Rectangular type engine shed:
In this type of engine shed, two parallel tracks are laid, which meet at one or both the ends.
The engine can come from one end and leave the shed in other end
They need more space; they are widely used in India

50. Rectangular type engine shed:

51. Engine sheds:

52. Circular type engine shed:

53. Circular type engine shed:
This type of shed consists of radiating tracks and a circular structure known as round house
A turn table is also provided with the help of turn table the incoming locomotive is put up on the un occupied track of the shed
Needs less place
Skilled labouris needed for the construction

54. Water Columns:
Awater craneis a device used for delivering a large volume ofwaterinto thetankortenderof asteam locomotive.The device is sometimes also called awater column.
As a steam locomotive consumes large quantities of water, water cranes were a vital part of railway stationequipment, often situated at the end of aplatform, so that water could be refilled during a stop at the station.
They are kept at all main line tracks at a distance of not less than 50Km.
It should not any obstruction to traffic
Foot valve is provided to regulate the water flow
Height of water column is 442cm
Projection of pipe is about 225 cms

55. Water Columns:

56. Water Column & Ash Pit

57. Ash pits:(Ash-pans)
Ash pits are provided to collect the ashes from the locomotives
They are generally 1.067m deep and length is slightly more than the length of the locomotive.
They rest on masonry or concrete walls and rails are fixed on longitudinal beams provided at the top of the walls

58. Turn table:
A turntable is a device used to turn railroad rolling stock.
Turntables were also used to turn observation cars so that their windowed lounge ends faced toward the rear of the train.
A turntable is a large circular platform which is used to turn locomotives and other rolling stock for railways.
A well-engineered turntable is designed in such a way that the efforts of only two or three people are needed to operate the turntable, even when dealing with very large and heavy locomotives
The reason the turntable was developed was because early steam locomotives were somewhat difficult to run in reverse
As a result, train companies started building turntables so that they could quickly turn their locomotives around.

59. Turn Table

61. Triangles:
Triangles are used for turning railway equipment
By performing the railway equivalent of athree-point turn, the direction of a locomotive or railway vehicle can be swapped around, leaving it facing in the direction from which it came
It consists of three short lengths of tracks laid to form a triangle and connected to each other by three pairs of points and crossings. Two tracks are laid in curves and third as straight.
The engine moves completely round the triangle and its direction is automatically changed

62. Triangle

63. Buffer Stops:
Abuffer stoporbumperis a device to preventrailway vehiclesfrom going past the end of a physical section oftrack
The design of the buffer stop is dependent in part upon the kind of couplings that the railway uses, since thecoupling gearis the first part of the vehicle that the buffer stop touches
It consists of timber beam 30x13cm section of the level of buffer on vehicles, fixed to the two vertical rail parts bolted to the track rails on other ends.

64. Buffer Stops:

65. Buffer Stops:

66. Fouling Marks:
Purpose is to avoid side collision between two trains on adjacent track.(in between diverging/converging tracking rear of t/in curve)
It should be fixed at the point where the spacing between the tracks begins to reduce to less than the minimum as specified in schedule of dimension.(i.e. 4.27 Meter track centre normally)
They are made up of stone or concrete blocks and painted in black and white

67. Fouling Marks:

68. Fouling Marks:

69. Examination pits:
Examination pits are similar to ash pits but they are used to examine the engines from underneath.
These pits are generally longer and deeper than the ash-pits
Provided in locomotive yards

70. Examination pits

71. Traversers:
Traversersare used to shift the position of the vehicles or locomotives sideways
They provide an arrangement of transferring engines and vehicles from one track to a parallel track
Traversersare preferred to turnouts, cross-overs, etc.
It consists of a platform mounted on rollers.
Vehicle to be shifted is placed on the traverserand then the traverse is moved sideways and adjusted to the parallel track where the vehicle is to be placed

72. Traversers:

73. Traversers:

74. Derailing switch:
A derailing switch is an ordinary point switch
The switch is open in the normal position and is generally provided near the dead end of the siding
Any vehicle passing over it shall be derailed because of break of continuity of rails

75. Derailing switch:

76. Drop Pits:
These are constructed at right angle to the track to examine and repair or to replace the old wheels by new ones.
In these pits the wheels of the locomotives are lowered and the wheels and axles are taken out with the help of different kinds of jacks

77. Drop Pits:

78. Scotch Block:
It consists of a block of wood placed on the rail and suitably held and locked in position
It forms an obstruction to the passage of vehicles and hence it prevents the escape of vehicle beyond the dead end of the siding

79. Scotch Block

80. Scotch and Sand Hump

81. Sand hump:
Method of checking vehicle
The rails in the dead end siding after some fixed distance get embedded in the sand and come to rest

82. Weigh Bridge:
These are level platforms with rails and are connected to the main track
The beam rests on the knife edge and attached to the lever to which loaded wagons come to the siding to the weigh bridge is fixed
The lever mechanism is activated and weight is indicated

83. Weigh Bridge

84. Weigh Bridge

85. POINTS AND CROSSINGS
Purpose for providing points and crossings:
It is the name given to the arrangement which diverts the train from one track to another, either parallel to or diverging from the first track.
Point and Crossings are peculiar arrangement used in permanent way (railway track) to guide the vehicle for directional change.

86. POINTS AND CROSSINGS

87. Some definitions:
1.Angle of crossing:
It is the angle between the running faces of point rail and splice rail
2.Branch Track:
Track to which train is diverted from main track
3.Check rails:
To prevent the tendency of wheel to climb over the crossing rail lengths are provided on the opposite side of the crossing
4.Heel block:It is the CI block to which tongue rail and lead rails are both bolted

88. Branch Track:

89. Check rails

90. Heel block

91. 5.Lead Rails: They are the rail which lead the track from heel of the tongue rail to the toe of the crossing
6.Nose of crossing: It is the point at which rail, splice rail, or two point rails meet.
7.Tongue rail:These are tapered rails
8.Switch:It consists of tongue rail and a stock rail
9.Throw of switch:Both the tongue rails move through the same distance or gap, this gap is known as throw of switch

92. Lead Rails

93. Nose of crossing

94. Tongue rail

95. Switch

96. Throw of Switch

97. 10.Switch angle:It is the angle formed between the gauge face of the stock rail and the tongue rail
11.Turn outs: A complete set of points and crossings along with a lead rail is known as turnout
12. Facing direction:If someone stands at toe of switch and looks towards the crossing it is called facing direction
13.Trailing directions:If someone stands at the crossing and looks towards the switches, then the direction is called Trailing direction

98. Switch angle

99. Turn outs

100. 14.Facing points or Facing turn outs: When the train pass over the switches first and then they pass over the crossing
15.Trailing points or Trailing Turnouts:The opposite side of facing points in which the trains pass over the crossings first and then over the switches.

101. Turnout

102. Right Hand Turn out and Left Hand Turn out:
If a train from main track is diverted to the right of the main route in the facing direction, then this diversion is known as Right-hand turnouts.
If a train from main track is diverted to the left of the main route in the facing direction, then this diversion is known as Left-hand turnouts.

103. Right Hand Turn out

104. Left Hand Turn out

105. Sleeper Laid for Points and crossing:
Two methods of laying sleepers below the points and crossing
1.Through sleepers
2.Interlaced sleepers

106. Through sleepers and Interlaced sleepers

107. 1.Through sleepers:
They are provided in the overall length of points and crossing
Through sleepers maintain several rails at the same level especially in straight and curved tracks.
Difficulties in the procurement and transporting of long sleepers

108. Through sleepers

109. 2.Interlaced sleepers:
Adopted when longer sleepers are not available
Both the tracks are laid on different sleepers, the curved track often deforms and causes difficulties in maintenance.
Also possess difficulties in the proper packing of the ballast

110. Interlaced sleepers

111. Through sleepers and Interlaced sleepers

112. Types of Switches:
There are two types of switches
(i)Stub Switch
(ii)Split Switch

113. (i)Stub Switch
Earliest type of switch. No separate tongue rails are provided
Some portion of the main tracks is moved from side to side
It is obsolete now and no more in use on Indian Railways

114. (ii)Split Switch
This the modern type of switch. It consists of a stock rail and a tongue rail.

115. Crossings:
It is a device provided at the intersection of two tails to allow the trail moving along one of the tracks to pass across the other
Types of crossing
(i)Acute crossing or Ordinary crossing
(ii)Double or obtuse crossing
(iii)Square crossing

116. Crossings:

117. (i)Acute crossing or Ordinary crossing
Acute angle is formed when a right hand rail of one track crosses left hand rail of another track at an acute angle

118. (ii)Double or obtuse crossing
This crossing is fixed when a track crosses another at an obtuse angle.

119. (iii)Square crossing:
When one track crosses another track of the same or different gauge at right angle

120. SIGNALLING:
General:
Railway signallingis a system used to controlrailwaytraffic safely, essentially to prevent trains from colliding
Signaling consists of the systems, device and means by which trains are operated efficiently and tracks are used to maximum extent, maintaining the safety of the passengers, the staff and the rolling stock.
It includes the use and working of signals, points, block instruments and other equipments.

121. SIGNALLING:

122. Objects of Signaling:
To provide facilities for the efficient moving of trains.
To ensure safety between two or more trains which cross or approach each other's path.
To provide facilities for the maximum utility of the track.
To provide facilities for safe and efficient shunting operations.
To guide the trains movement during maintenance and the repairs of the track.
To safeguard the trains at converging junctions and give directional indications of diverging junctions.

123. Types of Signal:
According to function
According to location
Special signals

124. (i)Classification according to function:
(a)Stop signals or semaphore type signals
(b)Warner signals
(c)Disc or ground signals
(d)Colouredlight signals

125. (a)Stop signals or semaphore type signals
One of the earliest forms of fixedrailway signalis thesemaphore.
These signals display their different indications totrain driversby changing the angle of inclination of a pivoted 'arm'
The stop position is the normal position and it is said to be ONposition
The arm can be lowered at an angle of 400to 600with horizontal and is said to be OFFposition

126. (a)Stop signals or semaphore type signals

127. (b)Warner signals:
The warnersignal is similar to semaphore signal in shape except a v-notch at free end, ie. The movable arm is fish tailed as shown.
The white band is also of v-shape
The warnersignal is placed on the same post of the semaphore signal 1.8 to 2.1m below the semaphore signal.
The warnersignal is painted yellow and exhibits yellow or amber colourat night instead of red colour

128. (b)Warner signals:

129. Shunting Signals:
These signals are used for shunting operations in station yards
They are of the shape of a circular disc with a red band on a white back ground
The disc can revolve in a vertical plane by pulling the lever by hand.
Two holes are provided, one for red lamp and the other for the green lamp.
When the red band is horizontal or shows red light at night it indicates ―STOP‖
When the red band is inclined at 45 degree or shown green light at night indicates ―PROCEED‖

130. Shunting Signals:

131. Shunting Signals:

132. Colourlight signals:
Semaphore signals are being replaced by high intensity beam colourlight signals both during day and night
In case of colourlight signals, the normal position is to indicate ―PROCEED‖ (ie., shows green light)
When the section is blocked, it automatically indicates ―STOP‖ or ―DANGER‖ (ie., shows red light)
In India these signals are used on urban and sub- urban sections with heavy traffic

133. Colourlight signals:

134. Colourlight signals

135. Locationalcharacteristics
(i)Reception signals
(a)Outer signal
(b)Home signal
(ii) Departure signals
(a)Starter
(b)Advance Starter

136. Location of signals

137. (a)Outer signal:
This is the first stop signal which indicates the entry of the train from block to the station yard
It should be placed at an adequate distance (0.54km for BG and 0.4 km for MG)
It has one arm but may have a warnersignal on the same post nearly 2m below it.
In the Stopposition the driver must bring his train to a stop at a distance of about 90m before the outer signal and then proceed to the home signal with caution
If it is in the Proceedposition then the driver can take the train at speed, assuming that home signal is also in the proceed position.

138. (b)Home signal:
Due to its location at the door of station, it is termed as Home signal.
The home signal has bracketed arms to indicate which line is to be used.
The function of home signal is to protect the sidings already occupied.
It is located at not more than 180m from the start of points of switches.
Home signals carry as many arms as the number of diverging lines.

139. (c)Starter signals:
It marks the limit up to which trains stopping at a station should come to a stand
The starter is the last stop signal at a station
It controls the movements of the trains when they depart from the stations.
No train can leave the station unless the starter signal shows the ―PROCEED‖ position (ie., inclined position)

140. (d)Advance Starter signals:
Besides the starter signal for each of the station lines from which trains starts, an advance starter may also be provided.
The advance starter becomes the last stop signal at the stations where is provided.
It is an indication for the train having left the station

141. Special Signals:
(i)Repeater or Co-acting signal:
When a train passes through a station without stopping, the driver comes across the five signals in this sequence WARNER, OUTER, HOME, STARTER and ADVANCE STARTER.
When the drivers vision is obstructed by an over bridge between the signals, a signal is provided with a duplicate arm of smaller size at a suitable position which repeats the indication of signal head. It is therefore termed as Repeater signal.
This signal is linked with the main signal and therefore, when the lever is pulled both signals are lowered simultaneously. Also called as ―co-acting signal‖

142. Repeater or Co-acting Signal

143. (ii)Routing Signal:
When various signals for main and branch lines are fixed on the same vertical post, they are known as routing signals.
Generally the signal for the main line is kept at higher level than that for branch line.

144. (ii)Routing Signal:

145. (iii)Calling-on Signal:
These consist of small and short arms fixed on the same post below main signals
A calling-on signal permits a train to proceed cautiously after the train has been brought to a halt by the main signal
This signals are helpful when repair works are going on

146. Calling-on Signal

147. (iv)Miscellaneous signals:
Various other devices are used for indicating signals. Signals are meant for goods sidings are distinguished by providing rings or writing capital letterSetc.,
Two crossed bars are put up on the signal which is under repair and it is placed in ONposition.

148. Control of movement of trains:
It is quite essential that movements of trains on particular tracks should be safe and for this purpose various methods are found out
(i)Following trains system
(ii)Absolute block system
(iii)Automatic signalling
(iv)Pilot guard system

149. (i)Following trains system:
Used in case of emergencies such as failure of telegraph and telephone systems.
In this method, a fixed interval of time is maintained between the departure of one train and the departure of the next train along the same time.
This fixed interval is worked out in such a way that sufficient distance or headway in maintained between the tail of the first train and the head of the next following train.

150. (ii)Absolute block system:
The principle of the absolute block systemofrailway signallingis to ensure the safe operation of a railway by allowing only onetrainto occupy a defined section of track at a time
Instead of a fixed interval of time between successive trains, a varying interval may be kept depending on the time, actually taken by particular trains.
It is a space interval system rather than a fixed interval system.
In the absolute block system the line is assumed to be blocked until the fact that the line is clear is established by some suitable information conveyed by block instruments
The electric telegraph provided the ability for signalmen to communicate with each other and provided the basis for the absolute block system

151. Absolute Block Diagram

152. (iii)Automatic signaling:
In order to avoid accidents, automatic signallinghas been found out. In this signals are operated by trains themselves.
An electric current is conveyed through the track when a train occupies that particular track and this current puts the signal at danger position until the train has gone far ahead so as to require no further protection

153. (iv)Pilot guard system:
Used on certain occasions such as breakdown of telephone and telegraph system on a single line and one track of a double line being out of order.
In this system, a pilot proceeds by one train to the station ahead and then he returns by a train running in the opposite direction.

154. Centralized Traffic Control:
Centralized traffic control(CTC) is a form ofrailway signallingthat originated in North America
The system consists of a centralized train dispatcher's office that controls railroad switches in the CTC territory and the signals that railroad engineers must obey in order to keep the traffic moving safely and smoothly across the railroad.
CTC systems are considered sufficient authority to run trains based strictly on signal indications. This is because CTC signals default to 'Stop' and require a human dispatcher to 'Clear' them.

155. Centralized Traffic Control

156. Interlocking:
Definition:
Inrailway signalling, aninterlockingis an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings
An arrangement of signals and signal appliances so interconnected that their movements must succeed each other in proper sequence".
In general terms an interlocking is a location where plain track ends and trackworkwith points and crossings complicate train movements. These areas are likely to be:-
Junctions where two or more main lines meet.
Complex yards or sidings are encountered. These may be at larger towns or depot facilities.
An interlocking provides for complex train movements and shunting of trains.
It provides for the protection of multiple train movements within a localised area.

157. Principles of Interlocking:
Not possible to lower the signals for the admissions of trains from opposite direction or converging directions at the same time to the same line
Not possible to lower a signal for any approaching train until the correct points
Not possible for loose wagons from any part of the yard to obstruct the line which is set for incoming train after lowering the signal
When the signal is lowered, it should not be possible to disconnect any point or reverse unlock the points until the train has passed and signals have been raised to its ―ON‖ position.
Not possible to lower warnersignal unless home and starting signals have lowered in advance

158. Methods of Interlocking:
The signals and points are operated by means of levers.
Levers are located at ground level or platform level or in an elevated structure called signal box or signal cabin
Interlocking is done by grouping levers at one point
The levers are painted for easy identification
There are three methods of interlocking
(i)Tappets and lock system
(ii)Key system
(iii)Route relay system.

159. (i)Tappets and lock system
This method is useful when levers are to be interlocked so as to prevent conflicting movement
The tappers are of steel sections. 38mmX16mm with suitable recesses and notches.
They are attached to the levers.
The locks are also of steel with shapes to suit the recesses in the tappers.
The lock move at right angle to the tappers

160. Working of Tappets and locks system:
The normal setting of the points is for the main line. The signal for the main line should be interlocked with the facing points so that when it is lowered, points cannot be changed. The levers are interlocked such that pulling one of them prevents the other being pulled. This is known as (1) locks (3)

161. The loop signal should be interlocked with the facing points such that it cannot be lowered unless the points are set for the siding. Also it cannot be lowered when the joints are set for main line. Levers (2) and (3) are interlocked so that the lever (2) cannot be pulled unless (3) has already been pulled.
Conversely lever (3) can be restored to its normal position only if lever (2) has already been restored to its original position. This is known as (3) release (2) or (2) back locks (3)
The outer signal should be so interlocked with the routing signal that it cannot be lowered until one of them is first lowered. When levers (1), (2) and (4) are interlocked so that lever (4) cannot be worked unless lever (1) or (2) has already been worked

162. The working of this system is given in the interlocking table below
Description of levers
Lever No.
Release
Locks
Backlocks
Main
1
4
3
-
Loop
2
4
-
3
Points
3
2
1
-
Outer
4
-
-
1,2

163. Tappet & Locks System

164. Tappet & Locks System

165. Key System:
This is the simplest method of interlocking. The key locks are manipulated in this system
Single lock and key system:
The principle of this system is to provide two locks which are worked by a single key. With drawl of the key locks the signal in the horizontal position and the points in the normal setting for the main line. And B are two locks operated by a single key. To lower the signal the key is inserted and turned in the lock B. This releases the signal and when the signal is lowered, it prevents the key from being withdrawn. Hence when the signal is lowered the point is correctly set for the main line. For using the siding, the key withdrawn from the lock B after restoring signal from normal position and inserted and turned in lock A. This releases the points which may then be set for siding. Now the main signal cannot be lowered.

166. Route relay System:
In this system, the points and signals for movements of trains are electrically operated. This is the mode and sophisticated system of interlocking. Due to this system there is a considerable saving of man power and maintenance expenditure of cabins.

167. Route relay System

168. Rapid Transport System:
General
Rapid transportis a type of high-capacitypublic transportgenerally found inurban areas.
Unlikebusesandtrains, rapid transport systems operate on an exclusiveright-of-waywhich is usuallygrade separatedintunnelsorelevated railways.
Metrois the most common term for underground rapid transport systems
Rapid transport is used incities,agglomerations, andmetropolitan areasto transport large numbers of people often short distances at highfrequency. The extent of the rapid transport system varies greatly between cities, with several transport strategies

169. Elevated railways

170. Mono Rail

171. Metro Rail in Chennai

172. Under ground railways:
The railways provided just below ground level are called ―low level or underground railways‖.
In this system of Railways, tunnelsare constructed for carrying tracks through them and a over -bridge is necessary at every road crossing to carry the road traffic over the railway traffic.
Due to ventilation problems in tunnels, electricity is the only source of power for traction in under ground railways.

173. Under ground railways:
Advantages :
This system provides rapid and unobstructed transportation.
This system helps in reducing traffic congestion problems.
This system provides safety during aerial attack in war.
Suitability :
Underground railways are suitable in the heavily congested urban areas where the traffic intensity on roads is heavy.

174. Under ground railways

175. Tube railways :
The railway provided underground at a greater depth of about 18 m or more (up to 52 m) are called tube railways.
This system of railways is so called as the section of the underground tunnels, carrying the track, is to avoid the interference of the tracks with waterand gas pipes, sewerage systems andoil or drainage pipes, etc
An electrically powered railroad with tracks running through a tunnel underground; a subway.

176. Some important features of the tube railways are given below :-
The railways stations have to be of cylindrical form.
Escalators or moving stair cases are to be constructed to reach the tube railways.
Only electric traction to be used to avoid the smoke and ventilation problems.
Automatic signaling system is to be used.
Such a mechanism of the train is to be used that it cannot start until all the doors are closed, and it automatically stops, if the signal is at ‗STOP‘ position.
This system of railways is used by the London Post Office in transporting mails through a small diameter tunnel with automatic control without any driver.

177. Tube railways :