MODULE III

Railway operation and control: Points and Crossings – Design features of a turnout –
Details of station yards and marshalling yards – Signaling, interlocking of signals and
points - Principles of track circuiting - Control systems of train movements – ATC,
CTC – track circuiting
1.1 Points and Crossings

Wheels of trains have flanges and direction of movement of trains is controlled by

wheel flanges. Hence special arrangements are needed in tracks to divert trains from
one direction to another direction
Points and crossings are arrangements, which divert trains from one track to another
either parallel or diverging from the first track.
A switch consists of a tongue rail and a stock rail. Tongue rails are made of thinner
sections at the toe of the switch. Tongue rails are supported on sliding plates and each
pair of tongue rail is connected by stretcher bars near the toe of switch so that both
the tongue rails move through same distance or gap. This gap is known as throw of
switch. A heel block or a distance block and fish plates are provided at the heel of
switch to connect tongue rail with stock rail. A set of switches consists of a left hand
switch and a right hand switch. A set of switches is known as points. If the train is
diverted to the right hand side as in Figure 3.1, the layout is known as right hand
turnout. If the train is diverted to the left hand side, the layout is known as left hand
turnout, ie looking from points towards crossing

Facing
direction

Figure 3.1-a Right hand turnout

 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.1 b Right hand turnout

The long, continuous rails that form the outside edges of the switch are called the
stock rails.

Facing points or facing turnouts are those, where trains pass over switches first and then
pass over the crossing.. Trailing points or trailing turnouts are on the opposite side of
facing points and in this case, trains pass over crossing first and then over switches.
Switches are termed as right hand switch and left hand switch as seen from facing
direction

Check or guard rails are provided to guide flanges of wheels of trains so that they do not
strike against the nose of crossing while moving in a facing direction. Check rails are
attached to running rails on either side of crossing as near to them as will just allow
the flange of the wheel of trains to pass. Short check rails range in length from 244
cm to 274 cm while long check rails range in length from 366 cm to 610 cm. Longer
check rails are used where the crossing number is large. Theoretical point where
gauge faces from both sides intersect is called Theoretical Nose of Crossing (T.N.C.).
Toe of the blunt nose is called Actual Nose of Crossing (A.N.C.)

. CE 407 Transportation Engineering II

2
 MEA Engineering College
_____________________________________________________________________________________________
3.1.1 Sleepers for Points and Crossings
i. Through sleepers
Through sleepers are laid in the overall length of points and crossings. Through sleepers
maintain several rails at same level. It is possible to fix alignment of curved track in
relation to straight track. Long sleepers are required in this arrangement.
ii. Interlaced Sleepers
Interlaced sleepers are used at points and crossings when there is a shortage of long
sleepers.

Figure 3.2 Through Sleepers

Figure 3.3 Interlaced Sleepers

With these type of sleepers, Super elevation or cant can be given to the out side of lead
rail and Curved track can be adjusted to a good curve without depending on the offsets
from straight track.

. CE 407 Transportation Engineering II

3
 MEA Engineering College
_____________________________________________________________________________________________
These sleepers have got the disadvantages like levels of straight track and curved track
vary, packing issue of sleepers and deformation of curved track after passage of
number of trains.
1.1.2 Steel for Points and Crossings
Special Steel is used for switches and crossings as there will be more wear and tear at
these points due to high speeds and heavy axle loads. Alloy steels like medium
manganese steel and high manganese steel are used for this purpose.3.1.3 3.1.3
Switches
Stub switches and Split switches are the two types of switches
Stub switch
Stub switch is the earliest form of switch. Some portion of the main track is moved
form side to side. This switch is replaced across the globe by Split Switch.

Figure 3.4 Stub Switch

Split Switch
A split switch consists of two parts, a stock rail and a tongue rail. Two types of split
switches are there

Figure 3.5 Details of Switch

i. Loose heel type or Articulated type switch
ii. Fixed type or spring switch or flexible switch

. CE 407 Transportation Engineering II

4
 MEA Engineering College
_____________________________________________________________________________________________
i. Loose heel type or Articulated type switch
Fish plates join lead rails to the tongue rail of the switch. Two front bolts are kept loose
to allow for the throw of switch. Due to this, heel joint becomes weak.. Figure 3.6
shows a typical layout of this type of switch.

Figure 3.6 Loose Heel type Switch

Loose heel switches are not favoured in new layouts because of the knocking caused to
the rolling stock by comparatively sharper change of curvature.

ii. Fixed type or spring switch or flexible switch

Fixed type heels have given satisfactory results compared to loose heel type switches,
but its use is limited to long switches. Tongue rail is held in its position with stock
rail at the virtual heel by means of heel or distance blocks. Switch can be hand
operated or by rod from a lever frame. Typical layout of this type of switch is given in
Figure 3.7. Lead rail is worked out in the normal way.

. CE 407 Transportation Engineering II

5
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.7 Fixed heel type switch

3.1.4 Shapes of Switches

Switches are divided into three types based on their shape
i. Undercut switches
ii. Straight cut switches
iii. Over riding switches or composite switches

i. Undercut switches

Tongue rail at the toe of switch is planed to a very fine edge at the top. Toe is
accommodated under the head of stock rail as given in Figure 3.7. Head of stock rail
is straight or slightly planed. Foot of stock rail is properly cut to accommodate foot of
tongue rail. Figure 3.8 shows old design as well as new design

Figure 3.8 Old and Modified undercut switch

ii. Straight cut switches

Tongue rail is kept straight in line with stock rail as in Figure 39. Thickness of the toe of
the tongue rail becomes thick and strength is increased.

. CE 407 Transportation Engineering II

6
 MEA Engineering College
_____________________________________________________________________________________________
Figure 3.9 Straight cut switch

Stock rail is joggled by an amount equal to the thickness of tongue at 13 mm from toe.
The joggled length is usually 152 mm. Gauge will increase over the joggled length of the
stock rail. Hence it is practice to provide straight cut switches for facing points and to
provide undercut switches for trailing points.

iii. Over riding switches or composite switches

Separate rail sections are adopted for stock rail and tongue rail. Stock rail is of heavy
section and tongue rail is of light section. Tongue rail rides over the foot of stock rail as
shown in Figure 3.10. In the modified overriding switch, tongue rail and stock rail are of
same section. But the tongue rail is kept higher than the stock rail by 6 mm for part of its
length. The difference in height is adjusted by putting special machined bearing plates
behind the heel.

Figure 3.10 Over riding witch and Modified over riding switch

3.1.5 Length of stock rails and tongue rails

Length of stock rail should be sufficiently longer than tongue rail to avoid formation of
rail joints near toe and heel of tongue rail., (Refer Figure 3.5) Length of tongue rail
ahead of toe of switch should be kept minimum, usually 1626 mm to 1676 mm.

Length of tongue rail depends on value of switch angle. Short tongue rail will increase
angle of switch while long tongue rails will increase overall length of turnout. A
length satisfying these conflicting requirements is required. Normally tongue rails are
longer than rigid wheel base of four wheel vehicle.

Length of straight switches adopted in Indian Railways based on practical

considerations, initial cost and length of lead in turnout is given here

. CE 407 Transportation Engineering II

7
 MEA Engineering College
_____________________________________________________________________________________________
B.G. 6400 mm and 4725 mm

M.G. 5485 mm

N.G. 4115mm

3.1.6 Heel divergence or heel clearance

Distance at the heel between gauge line of the switch and the stock rail is known as heel
divergence or heel offset or heel clearance. Heel divergence is equal to the flange
clearance plus width of head of tongue rail

3.1.7 Switch angle

Angle formed between gauge lines of stock rail and tongue rail is known as switch angle
or angle of switch divergence

Figure 3.11 –a. Heel divergence

. CE 407 Transportation Engineering II

8
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.11 b. Heel Divergence

Switch angle is function of length of tongue rail and heel divergence. If the switch
angle is more, entry of train will not be smooth and consequently speed of trains will
have to be reduced. Small switch angle will increase the overall length of turnout. Hence
smaller switch angles are provided on sections used by fast moving trains while greater
switch angles are adopted in the case of yards and other places where slow moving trains
are passing through

𝑑
𝑆𝑖𝑛 𝜃 =
𝐷

where, 𝜃 = 𝑠𝑤𝑖𝑡𝑐ℎ 𝑎𝑛𝑔𝑙𝑒

𝑑 = ℎ𝑒𝑒𝑙 𝑑𝑖𝑣𝑒𝑟𝑔𝑒𝑛𝑐𝑒

𝐷 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡𝑜𝑛𝑔𝑢𝑒 𝑟𝑎𝑖𝑙

Value of angle of switch will be changed when the tongue rail has some thickness at toe

𝑡 = 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 𝑜𝑓 𝑡𝑜𝑛𝑔𝑢𝑒 𝑟𝑎𝑖𝑙 𝑎𝑡 𝑡𝑜𝑒

D1 = actual length of tongue rail at toe

D2 = theoretical length of rail

x = difference between D1 and D2 = D2 - D1

!!!
𝑆𝑖𝑛 𝜃 =
!!

𝑑
𝐷2 =
𝑆𝑖𝑛 𝜃

. CE 407 Transportation Engineering II

9
 MEA Engineering College
_____________________________________________________________________________________________
!
or 𝑥=
!"# !

3.1.8 Throw of switch

Throw of the switch is the Distance through which tongue rails move at the toe of switch
to prepare one or other rail . Throw of Switch in India is adopted as 114 mm with
permissible values of 95 mm and 89 mm fro B.G. and M.G. respectively

3.1.9 Crossings

Crossing occurs when on rail crosses another rail. Crossings may be built up, cast in
place or combination of both. Built up crossings are very common, but they are not
suitable for fast and heavy traffic lanes. Cast crossings are suitable for fast and heavy
traffic lanes

Figure 3.12 a Details of crossing

. CE 407 Transportation Engineering II

10
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.12 b details of Crossing- Vee rails at crossing

3.1.10 Types of Crossings

Two types of crossings are there

i. Ordinary or acute crossing

ii. Double or obtuse crossing

i. Ordinary or acute crossing

Acute angle is formed either by a point rail and splice rail or by two point rails as given
in Figure 3.13

Figure 3.13 Point and Splice joint and Two point joint

Typical drawing of a Ordinary or acute crossing is given in Figure 3.14

. CE 407 Transportation Engineering II

11
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.14 Ordinary or acute crossing

ii. Double or obtuse crossing

Double crossing has two noses and is used in the formation of diamond crossing. Gauge
lines intersect at elbow as shown in Figure 3.15 Diamond crossing may be situated on
straight track or curved track. When the angle becomes 90 degree, it is known as square
crossing as given in Figure 3.16. This type of crossings should be avoided as far as
possible because there is a rapid wear of crossings and damage to rolling stock due to
heavy impact. When one track crosses another at an angle as given in Figure 3.17, a
diamond comprising of two acute crossings and two obtuse crossing is formed. Diamond
crossings should be avoided on curves as far as possible, or speed restrictions are to be
imposed on such crossings.

Figure 3.15Double or Obtuse crossing

. CE 407 Transportation Engineering II

12
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.16 Square Crossing

Figure 3.17 Diamond Crossing

3.1.11 Theoretical Nose of Crossing (TNC) and Actual Nose of Crossing (A.N.C)
Point rail cannot be manufactured to a well defined point as it would soon break away
under the impact action of moving trains. Hence a blunt nose is provided to the point
rail, thickness of which varies from 6 to 19 mm. This thickness is made equal to the
web of the rail. All calculation for the layout of crossing are generally made form the
theoretical nose of a crossing which is an imaginary point at which the point rail has
zero thickness. Position of theoretical point of a crossing from the actual nose of
crossing can be obtained by the following formula

𝑛=𝑁𝑋𝑡

n= distance between actual nose of the acute or obtuse crossing

N = Crossing number
T = thickness of crossing
3.1.12 Crossing Number

. CE 407 Transportation Engineering II

13
 MEA Engineering College
_____________________________________________________________________________________________
Crossings are generally designated in terms of distance required in spreading the point
and splice rails by 305 mm. Spread is measured between the gauge faces of rails and
the distance is measured from theoretical nose of the crossing as given in Figure 3.18

Figure 3.18 Crossing Number

Crossing number in common use in Indian Railways are 1 in 8 ½ , I in 12, 1 in 10 and
1 in 20. A flatter crossing may cause danger. Gap between the throat and nose of
crossing increases in this case and as a result chances of derailment of small wheels
are more
3.1.13 Crossing Clearance

Crossing clearance is the distance between the wing rail and crossing rail. Clearance
at the throat is theoretically same as the crossing clearance. But in actual, this is
slightly greater due to the fact that it is not possible to bend the wing rails to a fine
point at this spot. This fact is some times included in the design of crossings to
reduce the effect of shocks of wheels when they are moving over the crossing in the
trailing direction. Standard clearance of a B.G. is 44 mm

3.1.14 Crossing angle

Angle between gauge faces of the vee is the crossing angle

i. Right angle or Cole’s method

Figure 3.19 Crossing Angle Right angle method

. CE 407 Transportation Engineering II

14
 MEA Engineering College
_____________________________________________________________________________________________
∝ = 𝑎𝑛𝑔𝑙𝑒 𝑜𝑓 𝑐𝑟𝑜𝑠𝑠𝑖𝑛𝑔

𝑁 = 𝐶𝑟𝑜𝑠𝑠𝑖𝑛𝑔 𝑁𝑢𝑚𝑏𝑒𝑟

1
tan ∝ = 𝑜𝑟 𝐶𝑜𝑡 ∝ = 𝑁
𝑁

This is the standard method adopted for Indian Railways

ii. Centre line method

Measurement is taken along a line bisecting the crossing angle as in Figure 3.20

Figure 3.20 Crossing angle -Centre line method

1
∝ 1
𝑡𝑎𝑛 = 2 =
2 𝑁 2𝑁
∝
𝐶𝑜𝑡 =2𝑁
2

iii. Isosceles triangle method

Measurement is taken along one of the sides of an isosceles triangle as shown in

Figure 3.21

Figure 3.21 Crossing Angle Isosceles triangle method

𝟏
∝ 𝟐 𝟏
𝑺𝒊𝒏 = =
𝟐 𝑵 𝟐𝑵

. CE 407 Transportation Engineering II

15
 MEA Engineering College
_____________________________________________________________________________________________
∝
𝑪𝒐𝒔𝒆𝒄 = 𝟐𝑵
𝟐

3.1.15 Different types of leads

Three types of leads need to be calculated in the layout of points and crossings,
Switch lead, Curve lead and lead

Switch load is the distance from the springing of crossing curve to the heel of switch,
distance is measured along the straight

Curve lead is the distance from the springing of crossing curve to the theoretical nose
of the crossing , distance is measured along the straight

Lead is the distance from the heel of switch to the theoretical nose of crossing, the
distance is measured along straight track

Thus, Curve Lead = Switch lead + Lead

Figure 3.22 Leads for points and crossings

Method 1
An imaginary point at a slight distance ahead of toe of switch on straight main track is
considered as starting point of crossing curve. Theoretical nose of the crossing is
considered as end point of crossing curve. Crossing angle is formed at theoretical
nose of crossing as shown in Figure 3.22. By knowing Gauge G, Angle of crossing 𝛼
and heel clearance d, leads can be calculated. Notations used are given here

. CE 407 Transportation Engineering II

16
 MEA Engineering College
_____________________________________________________________________________________________

From triangle ABC,

𝛼 𝐵𝐶 𝐺
tan = =
2 𝐴𝐵 𝐶. 𝐿.
! !
𝐶. 𝐿. = ! = 𝐺 cot !
!"#
!

If O is the centre of the curve,

𝐷𝐶 𝐴𝐵 𝐶. 𝐿.
𝑆𝑖𝑛 𝛼 = = =
𝑂𝐶 𝑅𝑜 𝑅𝑜
𝐶. 𝐿.
𝑅𝑜 =
𝑆𝑖𝑛 𝛼
𝐺
𝑅 = 𝑅𝑜 −
2
(𝑡𝑎𝑛𝑔𝑒𝑛𝑡 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒)! 𝑆. 𝐿.!
𝑑= =
(2 𝑥 𝑟𝑎𝑑𝑖𝑢𝑠) 2𝑅𝑜
𝑆. 𝐿. = 2𝑅𝑜𝑑
𝐿 = 𝐶. 𝐿. −𝑆. 𝐿.
Three kinks will be formed in the rail, if calculations are made as per this method
a. A kink at the toe of switch
b. A kink at the heel of the switch as the tongue rail is not tangential to the
crossing curve
c. c. A kink at the toe of the crossing as the curve is carried theoretically up to
T.N.C., actually crossing is straight

Switch lead and curve lead are peculiar to this method only and they will not be
found in other methods
Use of this method is limited at present to industrial sidings, light section rails and
narrow gauges

Method II
Curve is tangential to the tongue rail in this method. Curve starts from the heel of
switch and ends at T.N.C.. Curve cuts other side of the main track at the crossing
angle.

. CE 407 Transportation Engineering II

17
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.23 Method II Calculation of leads

Hint. 2 sin A sin B = cos (A − B) – cos (A + B)

. CE 407 Transportation Engineering II

18
 MEA Engineering College
_____________________________________________________________________________________________
Kink at the heel of the switch is removed with the use of this method. This method
was previously used in U.K.

Method III

This method is similar to Method II, but crossing is also considered as straight.
Crossing curve starts from heel of switch and ends at toe of crossing or some other
point in advance of T.N.C. This distance is denoted by x. By knowing values of G, d,
𝛼, 𝜃 and x , lead and radius of curve can be worked out

Figure 3. 24 Method III-Calculation of leads

. CE 407 Transportation Engineering II

19
 MEA Engineering College
_____________________________________________________________________________________________

Hint. 2 sin A sin B = cos (A − B) – cos (A + B)

. CE 407 Transportation Engineering II

20
 MEA Engineering College
_____________________________________________________________________________________________
Kinks at heel of switch and toe of crossing are removed by applying this method.
Only one kink remains at the toe of the switch. Tongue rail and crossing are
considered straight and hence this method id correct. This method allows the use of
long, built up tongue rails and crossing of heavy rail sections. This method is widely
adopted in India, U.K. and U.S.A.

3.2 Combinations of Points and Crossings

Different turn outs can be formed by the use of points and crossings
i. Cross over
ii. Scissors cross over
iii. Slips
iv. Fixed point
v. Three throws
vi. Tandems or double turnouts
vii. Ladder tracks or gathering lines
viii. Gauntlet tracks
ix. Double junctions

i. Cross overs
Cross over facilitates movement of a train from one track to another track. Crossover
between two parallel railway tracks formed by two crossings of same crossing
number and joined by a straight portion between the reverse curve is shown in Figure
3.25

Figure 3.25 Cross Over 1

Portion between a and e is known as intermediate portion. Intermediate straight
distance B is required to find the relative positions of two crossings

. CE 407 Transportation Engineering II

21
 MEA Engineering College
_____________________________________________________________________________________________

Cross over may be provided under different conditions as given in Figure 3.26 to
Figure 3.29. Figure 3.26 shows a cross over between two parallel tracks which are
wide apart. Intermediated straight portion is not provided and curve are made to
reverse in direction from a point P. This arrangement will result in minimum total
length of cross over

Figure 3.26 Cross over -2

Figure 3.27, figure 3.28 and Figure 3.29 show cross overs on two un parallel tracks.
Distance PQ may be straight as in Figure 3.27. Angle of crossing at P in this case will
be more. If crossing angles at P and Q are equal, curved crossing at P should be
provided as shown in Figure 3.28

Figure 3.27 Cross over 3

. CE 407 Transportation Engineering II

22
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.28 Cross over 4

Arrangement to avoid curved crossing at P is given in Figure 3.29. Distance PQ is on
a curve

Figure 3.29 Cross over 5

Cross over between two curved concentric tracks and eccentric tracks is given in
Figure 3.30 and Figure 3.31 respectively. Intermediate portion PQ can be kept
straight or partly curved and partly straight or completely curved in both cases.

Figure 3.30 Cross over 6

Figure 3.31 Cross over 7

. CE 407 Transportation Engineering II

23
 MEA Engineering College
_____________________________________________________________________________________________
Cross over between three straight parallel tracks is shown in Figure 3.32. A diamond
crossing is required. If portion PQ is straight, all crossings will have same angle of
crossing.

Figure 3.32 Cross over 8

Cross over between three curved concentric tracks is given in Figure 3.33. Portion
PQ may be straight or curved. In the case of curved PQ, if radius of curve PQ is same
as that of the main track all crossing angles will be equal

Figure 3.33 Cross over 9

Problem
A crossover connects two parallel B.G. tracks of same crossing number of I in 8.5
with straight intermediate portion between reverse curve. Distance between centres
of track is 5.4 m. Find intermediate straight distance and overall length of cross over

Answer
Crossing number = 1 in 8.5
N = 8.5, 𝐶𝑜𝑡 𝛼 = 𝑁

𝛼 = 6.71 ≅ 6 ° 43ʹ↵

𝛼 = 6° 43ʹ

Intermediate Straight Distance,

𝐵 = 𝑁 𝑃 − 𝐺 𝑆𝑒𝑐 ∝ = 8.5 5400 − 1676 − 1676 𝑥 𝑆𝑒𝑐 6° 43

= 17310 mm
L =B + 4 GN =(17310 +4 x 1676 x8.5) = 74294 mm = 74.29 m

. CE 407 Transportation Engineering II

24
 MEA Engineering College
_____________________________________________________________________________________________

ii. Scissors Cross over

Scissors crossover consists of two cross overs with four pairs of switches and on
diamond. It is desired to have the crossing at Q, Figure 3.34, either well behind or
well ahead of crossing at P to properly support wheels of the vehicles when they are
passing over gaps. Scissors cross over is useful where space is limited where much
shunting has to be done. Scissors cross over is expensive and requires careful
maintenance

Figure 3. 34 Scissors Cross over

iii. Slips
Slips are provided to enable trains to pass from one track to other. Slips may be single
or double. A single slip consists of two sets of points put into a diamond as shown in
Figure 3.35. A train from A can travel either to B or D, in the case of single slip
While a train from C can travel only to D. A train from D can travel either to A or C
while a train from B can only ravel to A

Figure 3.35 Single Slip

. CE 407 Transportation Engineering II

25
 MEA Engineering College
_____________________________________________________________________________________________
Double slip consists of four sets of points put into a diamond as given in Figure 3.36.
Trains from A or C can travel either to B ro D and similarly trains from B or D can
proceed either to A or C.

Figure 3.36 Double Slip

iv. Fixed Point

Fixed points are used when two lines of different gauges have to pass through same
bridge by providing three rails and thereby saving expenditure of another bridge.
Three lines of rails will be laid, one rail common for both gauges. At points where
two lines diverge, fixed point is provided as given in Figure 3.37

Figure 3.37 Fixed Point

When a B.G. train pass through the line from left side to right side, wheel flanges on
right side will be forced into the space between fixed point and the running rail. If a
M.G. train is passing , wheel flanges on right side will be forced into the space
between guard rail and fixed point. Width of two gauges are maintained in the correct
position with tie bar in front of fixed point

. CE 407 Transportation Engineering II

26
 MEA Engineering College
_____________________________________________________________________________________________

v. Three throws
Three throws consist of two stock rails. Each switch has two tongue rails. Combined
heel blocks are provided for both tongue rails of same switch. Three throws switches
are not recommended for main lines or heavy fast moving fast lines. Provision of
double switches is dangerous and chances of derailment are there.

Three throws switches are useful in congested areas like, goods yard, entrance to
locomotive yards where saving of space is the important consideration. Tandem or
double turnputs are used in place of these switches. Radii of two turnouts will have to
be different for similar flexure type, Figure 3.38. Curves have to start at different
targets in order to bring the heel blocks in same line

Figure 3.38 Similar Flexure three throw

Radii of two curves are generally same and they start from a common tangent as
given in Figure 3.39

Figure 3.39 Contrary flexure three throw

vi. Tandems or double turnouts
Tandem turnout is a modification of three throw. Switches are not placed at the same
point in case of tandem turnouts. One set is placed behind the other. Distance between
two switches should be sufficient to allow room for usual throw of the point.
Tandem may be of similar flexure or of contrary flexure as given Figure 3.40 and
Figure 3.41 respectively

. CE 407 Transportation Engineering II

27
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.40 Similar Flexure Tandem

Figure 3.41 Contrary flexure Tandem

Tandem or double turnouts can be conveniently used in main traffic lines and they are
very much useful in congested areas where economy in space is main consideration

viii. Gathering lines or ladder tracks

Several lines are branching off from Gathering line or ladder track. Different
arrangements of Gathering lines are given in Figure 3.42, Figure 3.43 and Figure
3.44. AB represents a gathering line or ladder track and M represents main line

Figure 3.42 Gathering line 1

. CE 407 Transportation Engineering II

28
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.43 Gathering Line 2

Gathering line forms part of main line in the arrangement given in Figure 3.44

Figure 3.44 Gathering Line 3

Various combinations of these three types listed above can be made to have different
types of ladder tracks. Herring bone grid, one among these, is given in Figure 3.45

Figure 3.45 Herring bone grid

Angle made by ladder track with main track is known as gathering line angle. Ladder
track cannot be set at an angle less than crossing angle
𝑿
𝑺𝒊𝒏 𝜽 =
𝒀
𝜃 = 𝑙𝑖𝑚𝑖𝑡𝑖𝑛𝑔 𝑎𝑛𝑔𝑙𝑒 𝑜𝑓 𝑔𝑎𝑡ℎ𝑒𝑟𝑖𝑛𝑔 𝑙𝑖𝑛𝑒
X = distance between centres of adjacent tracks
Y = Overall length of points and crossings

Gathering line can be laid at crossing angle or any other angle which is greater than
the crossing angle but less than limiting angle.
Limiting angle of gathering line depends on methods adopted for calculating lead,
length of switches and crossings and spacing of tracks. Limiting angle is directly
proportional to spacing of tracks

viii. Gauntlet tracks

Gauntlet tracks are used when a double track is to be narrowed down for a short
distance of the track. This method cn be used when one of the double tracks is under

. CE 407 Transportation Engineering II

29
 MEA Engineering College
_____________________________________________________________________________________________
repair. Two tracks are simply laid side by side over sleepers and run together by using
two standard crossing but no switches

Figure 3.46 Gauntlet track

ix. Double junctions

Double junctions are required where there are two or more tracks and where
branches are taking off from main tracks. This consists of ordinary turnouts combined
with one or more diamond crossings as given in Figure 3.47 to Figure 3.3.50

Figure 3.47 Double junction 1

All junctions should be level on the main line. Junction will be on straight or curved
lines and branch line will be either single or double. Figure 3.47 shows a junction on
double straight main line with one branch line.
A double junction on double straight line with two branch line is given in Figure 3.48

. CE 407 Transportation Engineering II

30
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.48 Double junction 2

Curved main junctions with double main lines and double branch lines of similar
flexure and contrary flexure are given in Figure 3.49 and Figure 3.50 respectively.
Obtaining required super elevation on both lines is not possible.

Figure 3.49 Double junction 3

Figure 3.50 Double junction 4

. CE 407 Transportation Engineering II

31
 MEA Engineering College
_____________________________________________________________________________________________
1.2 Details of station yards and Marshalling yards

Station and yards are field control units of the railway system of communication and
they serve as waiting places for idle wagons. They also form basic administrative unit
of railway system of the country.
Station is defined as a place on railway line where traffic is booked and dealt with and
where an authority to proceed is given to the trains. In some stations, only one of thee
functions is carried out and accordingly they are classified as flag stations and block
stations.
Indian Railways has classified stations as Block stations, Non block stations and
Special Stations. Block stations are divided into three categories, Class A, Class B
and Class C
Class A- line on which the train is to be received is made clear for a distance of at
least 400 metres beyond the home signal or up to starting signal. Permission to
approach is then given to train
Class B- Permission to approach is given toe the train before the receiving line is
made clear within the station section
Class C – Block huts where trains do not stop
Non Block or D class stations are stopping places or flag stations. They are situated
between two consecutive block stations.
Special class stations are those which are not falling under A, B, C or D Class as
mentioned above
These classifications are meant for territories, which control movement of trains, by
Absolute block System. Stations are not classified in case of territories where
movements of trains are controlled by automatic signalling
3.2.1 Types of Stations
Stations can be divided into three types
1. Wayside stations
2. Junctions
3. Terminals

1. Wayside Stations
This type of station has arrangement for crossing of up and down trains or for
overtaking of slower trains by faster trains. Typical layouts for Single lane Wayside
station and Double Lane Wayside station are given in Figure 3.51 and Figure 3.52
respectively

Figure 3.51 Wayside station for single line

An island platform completely surrounded by tracks is formed in Figure 3.52. A foot
over bridge is provided for the movement of passengers

. CE 407 Transportation Engineering II

32
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.52 Wayside station for double lines

Branch lines are sometimes extended up to some portion of the main platform given
in Figure 3.53 to facilitate easy transshipment of passengers. This portion of main
platform on branch line is known as Dock platform

Figure 3.53 Dock Platform

2. Junctions
Branch line meets the main line in this type of stations. Arrangemtns are made in
these types of stations to facilitate interchange of traffic between main and branch
lines and clean and repair vehicles of the trains which terminate at junctions.
Junctions may occur between single branch line and single or double main lines or
between double branch lineand main tracks as shown in Figure 3.54 and Figure 3.55.
Figure 3.54 shows junction between a single

Figure 3.54 Junction 1

. CE 407 Transportation Engineering II

33
 MEA Engineering College
_____________________________________________________________________________________________
Branch line and single main line. Loop is provided on the branch line so that train
can be taken back along the same route. Cross over between main and branch line
shows the physical connection between two lines. Arrangement for the junction
between single branch line and double main lines is shown by means of dotted lines in
Figure 3.54. A foot over bridge is to be provided to facilitate interchange of traffic
between main and branch lines.
Junction between double branch line and main line is given in Figure 3.55. Cross over
between M1 and M2 enables the train of branch line B1 to proceed on branch line B2

Figure 3.55 Junction 2

Arrangement for junction between a single branch line and main tracks is shown by
means of dotted lines in Figure 3.55. Turnout is provided as shown and the remaining
portion of branch line B2 is eliminated

3. Terminals
Terminals or terminal junctions are stations at which railway line or one of the
branches terminates or ends. Additional arrangements like facilities to reverse
engines, number of sidings and examination pits are provided in terminals. Simple
layout of a terminal is given in Figure 3.56

Figure 3.56 Terminal

. CE 407 Transportation Engineering II

34
 MEA Engineering College
_____________________________________________________________________________________________
Hydraulic buffers are provided at the ends and locomotives are restricted from
touching the hydraulic buffer. Penalty is imposed on driver fro any violation. Ticket
office , restaurant, waiting rooms for passengers etc. are provided and connected to
roads so that passengers can make use of road vehicles to continue their travel
Siding
Siding is a low-speed railway track section different from a running line or through
route such as a main line or branch line. It may connect to through track or to other
sidings at either end.
Sidings often have lighter rails, meant for lower speed or less heavy traffic, and few
signals, if any.
Sidings connected at both ends to a running line are commonly known as loops
Platforms
Two types of platforms are provided
1. Passenger Platforms
2. Goods platforms

Figure 3.57 Platform

1. Passenger Platform
Constructed for the movements of passengers who are using railway. Platform should
be covered for a minimum distance of 61 metres of their length. Minimum width of
3.60 m of platform should be paved. Ends of platform are general in the form of ramp
of maximum slope 1:6. Sufficient arrangement of lighting and drinking water should
be made on passenger platforms. Names of stations should be written on an RCC
Board in Hindi in Devanagri script, English and regional language, if Hindi is not the
regional language of the area. Boards are at right angle to the track and provided at
the extremes of platforms. Height of the board should be at least 1.80 m from
platform level to the bottom of board. Board has yellow background and letters are in
black of size 300 mm and spacing between letters and top and bottom is 150 mm
Dimensions of platforms are determined as given here
Length
Length of the platform is decided by the length of longest train excluding length of
engine likely to use platform. Minimum length of platform for all gauges is about
183 metres. Desirable length of passenger platform for B.G. is 305 metre. Width of
passenger platform varies and it should not be less than 3.60 m
Distance from track
Edge of the platform should be at sufficient clearance from the centre line of the
railway track. Distance D as shown in Figure 3.57 is 1676 mm for B.G., 1346 MM for
M.G. and 1219 mm for N.G.
Height

. CE 407 Transportation Engineering II

35
 MEA Engineering College
_____________________________________________________________________________________________
Height of platform with respect to the rail level may be at high or low or rail level.
High level platforms are not preferred due to chances of accidents to passengers,
delays in passenger boarding and alighting and interference of platform structure with
track repairs. Height H of the platform from track level as given in Figure 3.57 is
given as follows
For B.G. 762 mm to 838 mm
For M.G. Rail level or 305 mm to 400 mm
For N.G. Rail level or 406 mm to 229 mm
2. Goods platforms
Goods platforms are similar to passenger platforms. They are at higher level than
passenger platforms and minimum width of goods platform in India is 3 m. Heights
of goods platform above rail level are 1067 mm for B.G., 686 mm for M.G. and 610
mm for N.G. Goods sheds should be provided on goods platform with arrangements
for weighing. Direct access should be given from goods platform to goods sidings and
to marshaling yard. Layout of goods platform should facilitate the efficient loading
and unloading of goods are carried out
3.2.2 Yards
Yard is a system of tracks laid within definite limits for various purposes such
as storing of vehicles, making up trains, dispatch of vehicles etc. over which
movements not authorized by time table may be made, subject to the prescribed rule,
regulations and symbols
Types of yards
Classification of railway yards is made into following four categories
1. Passenger Yards
2. Goods Yards
3. Marshalling yards
4. Locomotive yards
1. Passenger Yards
Passenger yards provide facilities for the safe movements of passengers and vehicles
for passengers. Passenger platforms may be considered as passenger yards. At
junctions or terminals, separate sidings are provided to accommodate passenger trains
during idle period
2. Goods Yards
Goods Yards are provided for receiving, loading and unloading of goods. Goods
platforms may be considered as goods yards. Separate goods sidings also have to be
provided
3. Marshalling Yards
Main function of marshaling yards is to segregate goods wagons received from
various centres in the order of station at which they are to be sent. Marshalling yards
are working as distribution centres. Empty wagons are kept in marshaling yards and
these can be supplied when required by other stations
Important points to be considered in the design of marshaling yards are given here
i. Marshalling yards should be designed such that shunting operations should not
disturb the time table of regular trains
ii. Design should be such that maximum number of wagons are despatched from
marshalling yards in a given period
iii. Future expansion needs due to increase in goods traffic need to be considered
while designing the marshaling yard
iv. Marshalling yards should be constructed at all important stations, especially where
main routes are converging

. CE 407 Transportation Engineering II

36
 MEA Engineering College
_____________________________________________________________________________________________
v. Marshalling yards should be laid parallel to the running lines as far as possible
vi. Design of marshaling yards should be such that wagons move in one direction
vii. Transship platforms with necessary repairing facilities should be provided on one
or more sidings of marshaling yard. Goods can be taken out from the defective wagon
and reloaded to another wagon by use of transship platform
viii. Adequate lighting arrangements and communication facilities like telephone lines
are provided in Marshalling yards
Features of Marshalling yards
Ideal layout of a marshaling yard consists of following three types of sidings
i. Reception sidings
ii. Sorting sidings
iii. Departure sidings

Figure 3. 58 Marshalling yard- Reception sidings

i.Reception sidings
Reception sidings are used to receive incoming trains. These are generally laid in the
form of grids with sidings of equal length. Incoming goods trains enter reception
sidings and wait for their turn for shunting operations
ii. Sorting Sidings
Sorting sidings are used during shunting operations. Each siding is allocated to
wagons bound for particular direction. Sorting sidings are generally laid in the form
of a fan or balloon. Number of sorting sidings required will depend on maximum
number of destinations for which traffic has to be sorted out

Figure 3.59 Marshalling Yard- Sorting Siding

iii. Departure Sidings

. CE 407 Transportation Engineering II

37
 MEA Engineering College
_____________________________________________________________________________________________
Departure sidings are similar to reception sidings and may be omitted in certain cases.
Number of sidings required for reception and departure sidings depend on following
factors

a. Maximum number of goods trains to be marshaled at the same time

b. Time required to marshal each train
c. Intensity of traffic on main lines and
d. Time required for inspecting the wages of incoming train for possible defects

Figure 3.60 Marshalling Yard- Departure Siding

Types of Marshalling yards

Three types of marshaling yards are there, flat yards, gravitstion yards and hump
yards
a. Flat yards
All sorting work is done by means of locomotives and hence requires more
consumption of power. This type is more suitable in places where limited space is
available for the layout of marshaling yards
b. Gravitation yards
In this type of yard, tracks are laid at suitable gradient so that wagons move due to
gravity and brakes are used to control movement of wagons. Thus shunting operations
are carried out by gravity assisted b engine power. This type of arrangement is
possible where topography is suitable
c. Hump yards
Humps or man made hills are constructed and wagons are pushed up to hump by
engine. After this, wagons are allowed to gravitate down the slope. Shunting
operations are carried out more quickly in hump yards, compared to gravitational or
flat yards. Normally a rising gradient of 1 in 150 or 1 in 175 is provided at the
pushing end for a length of about 183 metres. Then the hump is kept leveland it is
followed by falling gradients of 1 in 50, 1 in 150 and 1 in 300 and then level as given
in Figure 3.61

. CE 407 Transportation Engineering II

38
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.61 Hump yard

Individual wagons are stopped by applying wagon brakes, use of retarders and skids.
In India, skids are used . Skids may be placed on rails. Moving wagons will drag skid
and friction thus developed will prevent further movement of wagon.
Action of hump yard is little uncertain due to factors like climatic conditions,
different types of axle boxes and weight of wagons

Locomotive Yards
Locomotive yards are provided for cleaning, servicing, repairing, watering, oiling etc.
of locomotives. Typical layout of a locomotive yard is given in Figure 3.62
Essential requirements of a locomotive yard are

Figure 3.62 Locomotive Yard

i. There should a clear run from traffic yard to turn table

ii. Turntable should not make any obstructions to any locomotives that are entering
yard
iii. Loop line for the fuel platform shall be long enough to accommodate longest train
iv. Engine shed shall accommodate maximum number of engines likely to come for
repair at the same time
v. Overhead tank and loco well should be near the loco shed as far as possible
vi. Sick sidings should be easily accessible from locomotive yard

Level Crossing
Level crossing is provided when a railway line and road surface meet at same level.
Surface of road is kept at rail level and grooves are left along the road surface.

. CE 407 Transportation Engineering II

39
 MEA Engineering College
_____________________________________________________________________________________________
Grooves are provided with guard rails which are generally spiked to the wooden
sleepers. Typical layout of a level crossing is given in Figure 3.63

Figure 3.63 Level Crossing

Turntable
Turntable is used for changing the direction of engine. They are provided at important
stations where space is limited.
Turntable consists of a track on platform which is supported by a pair of girders.
Girders are supported on central pivot. Turntable is circular in shape and is installed
in a circular pit. Two or more tracks radiate from the periphery of circle of pit.
Engine is brought on the tuntable and after loosening the locking bolts, turntable is
rotated.. Then placed on the same track after a rotation of 180 degree or any other
track with suitable rotation. Diameter of the turntable should be long enough to
accommodate longest engine using turn table

Figure 3.64 Turntable

Triangles
Triangles are constructed for changing direction of engines. Triangles require large
areas. Generally triangle consists of three tracks. Typical layout is given in Figure
3.65

. CE 407 Transportation Engineering II

40
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.65 Triangle

3.3. Signalling
Signalling is an important part of railway engineering, which helps to avoid accidents
in railway tracks by way of passing on indications to Loco pilots of trains passing
through tracks

3.3.1 Objectives of Signalling

i. Provide safety to passengers, staff and rolling stock by avoiding accidents
ii. To maintain safe distance between trains travelling in the same direction of a
railway track
iii. To provide protection to trains at converging junctions and give directional
indications at diverging junctions
iv. To allow trains to travel at restricted speed during maintenance and repairs of
track
v. Provide protection to trains for carrying out shunting operations safely
3.3.2 Types of Signals
i. Classification according to function
ii. Classification according to location
iii. Special Signals

i. Classification according to function

a. Stop signals or Semaphore type signals
b. Warner Signals
c. Disc or ground signals
d. Coloured light signals
a. Stop signals or Semaphore type signals
A semaphore signal has following parts
i. Signal post
ii. Semaphore arm
iii. Lamp
iv. Spectacles
v. Pulley or drum
vi. Cam and fulcrum
vii. Crank rod
viii. Weight lever
ix. Signal wire
x. Chain
xi. Spindle
xii. White band

. CE 407 Transportation Engineering II

41
 MEA Engineering College
_____________________________________________________________________________________________

Typical section of a stop signal or semaphore signal is given in Figure 3.66

Figure 3.66 Stop signal or Semaphore Signal

A horizontal semaphore arm is fixed to a vertical post and is provided at its back side
with suitable arrangements to indicate red and green lights. Semaphore arm is 1676
mm long and 356 mm wide. It is designed such that its weight at the smaller end is
sufficient ot make it stand on the horizontal position normally. The semaphore signal
is placed with vertical post on the left hand side on the direction of motion.
Semaphore arm project towards the track for which it gives signals. Side of the arm
facing the driver is painted with vertical white band. Height of centre of arm above
ground level is about 7470 mm
A crank or any other device which is fixed on a horizontal pin on which the
semaphore is also fixed so that they move together
A crank rod to move the crank is provided
A weight lever revolving about a pin is provided. Counter weight is attached to one
end of lever through a cam. To the other end of the lever is attached signal wire which
is taken down over pulleys to the signal cabin
A ladder is provided for the physical connection between the semaphore arm and the
ground level
Working of Semaphore arm
Semaphore arm can take up to two positions namely horizontal and inclined. Normal
position of the signal is horizontal. It can be lowered by pulling the wire from signal
cabin..
Horizontal position indicates stop or danger. When the semaphore arm is lowered at
an angle of 40 degree to 60 degree it is said to be in off position, indicating proceed.
Red light for stop and green light for proceed is given during night.

b. Warner Signals
Warner signals are similar to semaphore signals except that a v notch is provided at
the free end of semaphore arm as given in Figure 3.67. Main function of this signal is
to warn the driver and is placed ahead of the ordinary semaphore signal. It is often
fixed on the same vertical post carrying outer signal. When the warner signal is in the

. CE 407 Transportation Engineering II

42
 MEA Engineering College
_____________________________________________________________________________________________
horizontal position, it indicates the signal ahead is in stop or danger position. If the
warner signal is in the inclined position, it indicates the signal ahead is in off position
and driver can proceed without any danger. On some railway lines of Indian railways,
warner signals are provided with yellow lights instead of red lights during night time

Figure 3.67 Warner Signal

c. Disc signal or ground signal.
These signals are also known as shunting signals as they are used in shunting
operations for low speed movements. Shape of these signals are circular with a red
band on a white background. Circular disc is rotated by suitable arrangements when
signal has to indicate proceed position, then red band assumes inclined position as
shown in Figure 3.68. Two holes are provided, one for red lamp and other for green
lamp. Red and green lamps are used for the stop and proceed indications respectively
at night .

Figure 3.68 Disc Signal

. CE 407 Transportation Engineering II

43
 MEA Engineering College
_____________________________________________________________________________________________

d. Coloured light signal

Figure 3.69
Coloured Signal
Coloured light signals give indications by electric lights automatically. They
generally consist of three lights fixed on a vertical post. Height of the vertical post is
sufficient to ensure the signal is at the driver’s eye level. Special lenses and hoods are
provided to protect lights so that they are visible even in sun light. Red light indicates
stop, yellow or amber indicates proceed cautiously and green light indicates proceed.
Normally signal remains in off or proceed position and as soon as train enters
sections, signal automatically changes to stop or on position. This is the main
difference between coloured light signals with ordinary semaphore signals

ii. Classification according to location

According to location, signals are classified into four, figure 3.70
a. Outer signal a. Home signal
c. Starter signal d. Advanced Starter signal
a. Outer signal
A train in motions needs certain distance to stop. This distance depends on speed of
train, weight of train, brake power of locomotive, and gradient of track. The distance
to stop is found to be 0.54 km for B.G. and 0.40 km fro M.G. for the maximum
allowable speed in India. First signal is provided at this distance beyond station limit
and is known as outer signal. In the stop position, it indicates that the driver must
bring the train to a stop at a distance of 9m before outer signal and then proved to
home signal with caution. Driver can continue to travel without stop if the outer signal
is in proceed indication. It indicates the home signal is also in the proceed indication

. CE 407 Transportation Engineering II

44
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.70 Type of Signals according to location

b. Home Signal

Home signal is provided exactly at the station limit. Its main function is to protect
station and junctions. Home signal gives permission to enter the platform. Maximum
unprotected distance between home signal and points it is intended to protect is 180
m. If this distance is more suitable means such as track circuits, locking bars etc.
should be provided to protect track

c. Starter signal
Starter signal controls the movement of trains as they leave stations. This signal is
provided on the forward end of platform.. Trains cannot leave platform unless starting
signal is lowered.
d. Advance Starter Signal
Shunting operation is done with protection of advance starter signal. These signals are
in the form of disc or ground signals, dwarf semaphores or any other approved form
with small lights. Sufficient space should be kept between signals and cross overs or
sidings so as to accommodate maximum likely length of train

iii. Special Signals

a. Routing Signals
b. Repeating Signals
c. Co acting Signals
d. Calling on signals
e. Indicators
f. Miscellaneous signals

a. Routing Signals

Signals for main and branch lines fixed on same vertical post are called routing
signals. Signal for the main line is kept at a higher level than for the branch line
normally, figure 3.71.

. CE 407 Transportation Engineering II

45
 MEA Engineering College
_____________________________________________________________________________________________

Figue 3.71 Routing Signal 1

Figure 3.72 Routing Signal 2

b. Repeating Signals
Repeating signals are used when vision of main signal is obstructed . They are also
required signals are required on curves near station. They are provided on separate
posts to convey information of signals to driver
c. Co acting Signals
Co acting signal is a Duplicate signal which is provided when the sight of a main
signal is not continuously visible because of a tunnel or bridge or due to any other
reason. Co acting signal is fixed in the same post at a lower level and it works
together with the main signal so as to repeat indication of main signal
d. Calling on signals

. CE 407 Transportation Engineering II

46
 MEA Engineering College
_____________________________________________________________________________________________

Calling on signals consist of small and short arms fixed on the same post below main
signals. Calling on signal permits a train to proceed cautiously after the train has been
brought to a halt by main signal. Calling on signals are helpful when repair works are
going on.
e. Indicators

Indicators are provided to give special information to drivers. They are painted in
black letters or figures on yellow background.
Shunting limit boards are rectangular boards of size 610 m x 915 mm with words
SHUNTING LIMIT. They are provided at a height of 2130 mm from rail level and
are fitted with lamp showing white light at night in both directions. Shunting
operation is prohibited beyond indicators.
Whistle indicators indicate point at which driver should whistle and it is provided
before level crossings and at places where sight of driver is obstructed. Whistle
indicator consists of 610 mm square board with 305 mm high letter W. It is provided
at a height of 2130 mm from rail level.
f. Miscellaneous signals
Various other devices are used for signal indication. Signals which are meant for
goods sidings are provided rings or writing capital letters S etc. Two crossed hairs are
put up on signal which is under repair and it is placed in on position. Bridge signal
provided at a bridge ahead of station where number of lines are converging is another
example of miscellaneous signal.

3.3.3 Typical layouts of signals

Typical layouts of signals are discussed here

1. Signalling at diverging junction
A simple diverging station is shown in Figure 3.75. One outer signal, semaphore or
warner type is provided. Routing signal is provided near facing points.

Figure 3.73 Signalling at a diverging junction

2. Signalling at converging junctions

Layout of signaling at a branch line converging to t main line is given in Figure 3.74

. CE 407 Transportation Engineering II

47
 MEA Engineering College
_____________________________________________________________________________________________

m
402

Figure 3.74 Signalling at a converging junction

Home signal for branch line is provided at an arbitrary distance of 402 m from fouling
point and separate outer signals for main and branch lines are provided. Fouling
point is the minimum safe distance between two converging lines to avoid collision
of trains.

3. Signalling at junction of two main lines and two branch lines with sidings

Typical layout of Signalling arrangement for double main line

Figure 3.75 Signalling at a junction

Details are given here
1. Down main outer
2. Down main home
3. Down branch outer
4. Down branch home
5. Down main starting
6. Down main advanced starting
7. Disc signal for up line to down platform
8. Disc signal for down platform to up line
9. Disc signal for up platform to down line
10. Disc signal for down line to up platform
11. Disc signal for siding to down line
12. Disc signal for no 10
13. Disc signal for down line to siding

. CE 407 Transportation Engineering II

48
 MEA Engineering College
_____________________________________________________________________________________________
14. Up branch advance starting
15. Up branch starting
16. Up main advance starting
17. Up main starting
18. Up main home
19. Up main outer

1.3.4 Control of movement of trains

In order to ensure safe movements of trains through railway tracks various methods
are used. These methods are
1. Following trains system
2. Absolute Block System
3. Automatic Signalling
4. Plot guard system
5. Centralised Traffic Control System
6. Cab Signalling system
7. TGV signaling system

1. Following trains system

This system is earliest form for movement of trains. At present used only in some
cases of emergencies. Fixed interval of time is maintained between the departures
of successive trains along a railway line. Sufficient distance between trains is
maintained in this system.
2. Absolute Block System
Varying time interval between successive trains along a railway line is kept
depending on the time actually taken by particular trains. Absolute Block system is a
space interval system rather than a time interval system. In the following trains
system, line is assumed to be clear after a certain fixed interval of time has passed.
In Absolute Block system, the line assumed to be blocked until the line is clear.
Instruments are installed at different blocks to convey information of train in the
block.
Track is divided into number of sections which are known as blocks or block
sections. Block section is the distance between two successive stations. Block
instruments in pairs are installed at each station. These instruments show whether
section ahead is clear or reserved fro a train. Thus it is arranged only one train
occupies one block section at a time. Station master gives indication to proceed to
the driver after verifying that there is no train in the block section.
Some branch limes where traffic is light, telephone may be used conveniently
instead of block instruments. Working of block instruments in a simple case is
illustrated in Figure 3.76

Figure 3.76 Absolute Block System

. CE 407 Transportation Engineering II

49
 MEA Engineering College
_____________________________________________________________________________________________

Block section between two signal boxes A and B is shown in Figure 3.76. Block
instruments are provided in each signal box and their purpose is to display similar
indications to both signal men simultaneously. Indications in this case are controlled
by signal man at B by the operation of keys or handles on his instrument
Operations are carried out as given
i. Signalman at A asks signalman B whether the section is clear or not
ii. If the section is clear at B, signalman at B acknowledges the signal and operates the
key or handle in his signal box indicating line clear
iii. This information is displayed on both signal boxes at A and B
iv. Signalman at A lowers his starting signal and allows train to proceed towards B
v. Signalman at A sends a signal to the signalman at B indicating train entering
section
vi. Signalman at B acknowledges the signal and places the block indicators at the
Train in Line position
vii. Signalman at B operates home signal at B
viii. Signalman at B then send message to next station ahead and procedure is
repeated
ix. As soon as train leaves station B and has passed the starting signal at B, signalman
at B brings his block instruments in the normal position and this gives Train Out of
section signal at A

3. Automatic Signalling
Automatic signaling system can avoid accidents due to negligence on the part of
human beings,
In this system, the 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 train has gone far ahead
so that no further protection is required
The electricity is transmitted to an electric locomotive either through overhead lines
or third rail. The former is known as catenary system and the locomotive obtains the
current through a retractable collecting device known as a pantograph.
In the latter case, a metal contact shoe which slides along the charged third rail is
provided outside the running rails and electric current is transmitted through this
metal shoe.
4. Plot guard system
Pilot guard system is used only in cases such as
i. break down of telephone and telegraph system on a single line
ii. one track of a double line out of order
In this system , a pilot guard proceeds by one train to the station ahead and then he
returns by a train in the opposite direction. No other train is allowed to move from the
station till the pilot guard returns with the train from opposite direction. The pilot
guard then again proceeds with a train in the same direction and the process is
repeated.

5. Centralised Traffic Control (CTC) System

In this system, a control room is provided from which the points and signal are
operated. The signal cabins are not required. The points and signals are suitably
interlocked and an illuminated diagram is provided in the control room to view the

. CE 407 Transportation Engineering II

50
 MEA Engineering College
_____________________________________________________________________________________________
movements of trains. This system is briefly known as the CTC system and it was first
introduced in U.S.A. in July 1927.
In CTC system, the controller arranges for all crossings and overtaking of goods and
passenger trains. The drivers of the trains are supposed merely to respect the
indications given by the signals prior to and near the point of execution. The
arrangements are made in CTC in such a way that the controller cannot authorise
conflicting train movements. Also, in case a driver does not respect a signal
indication, the stop signals are automatically displayed in advance and thus the
movements of trains are stopped to avoid a collision.
The cost of providing CTC on a particular track depends on various factors such as
existing method of directing trains, traffic density, spacing of sidings, changes in
signalling, track capacity to be increased, local conditions, etc. The advantages of
CTC are as follows:
(i) For single line operation, the CTC is considered to be most outstanding
development in railway field
(ii) It is possible for the controller to beforehand and then he arrange train movements
may attend to other office work.
(iii) The defects of track such as broken rails can be easily found out when this system
is adopted.
(iv) The points and signals can be operated in less than 30 seconds by push button
arrangement.
(v) The track capacity is considerably increased as the controller can take
instantaneous decisions.
(vi) The train can be run constantly at the maximum permissible speed since driver
does not have to watch for signal. If the signal is in stop position, the driver is warned
by means of loud whistle or red light in his cabin. If driver is not alert to respect such
warnings even then, the brakes are automatically applied and the train is stopped.
in India, this system was introduced in 1966 over 179 km of single line track on the
North Eastern Railway. It is found that the track capacity of this section has increased
by about 50 per cent. On Southern Railway also, the CTC system has been provided
on Chennai-Tambaram section from 1969.
(6) Cab signalling system
It is a method, where signals are waved to the train driver in his cab, usually from a
trackside induction system. Cab signalling is a railroad safety system that
communicates track status information to the train cab, where the engineer or driver
can see the information. The simplest systems display the trackside signal aspect
especially, green, yellow or indicating whether it is safe to proceed or not Some more
sophisticated systems also display allowable speed, location of nearby trains and
dynamic information about the track ahead. In modern systems, a speed enforcement
system usually overlays the cab signalling system to warn driver of dangerous
conditions and to automatically apply the brakes and bring the train to a stop if the
driver ignores the dangerous condition. Cab signaling system is used in in Konkan
Railways.
(7) TGV signalling system
TGV means Train a Grande Vitesse in French i.e., a high-speed train.
The signalling of a high speed line requires a different approach from railways. Due
to very high speed of train, driver cannot reliably read signals placed at trackside. The
TGV signalling system relies exclusively on cab Signalling, a system by which by
which signalling information is transmitted through the rails as electrical signals
which are picked up by antennas placed under the train. This information is then

. CE 407 Transportation Engineering II

51
 MEA Engineering College
_____________________________________________________________________________________________
processed by computer and displayed to the driver in the cab. Cab signalling is not a
new concept and is commonly used around the world for speed about 160 km/h. The
type of cab signal used on the TGVsystem is Transmission Voie-Machine or track to
train transmission
The TVM system was developed by the French group CSEE. It uses track circuits in
both rails to transmit signalling information to the train's on-board computers, as well
as fixed inductive loop beacons. It is one of the more advanced railway signalling in
the world. TVM-300 was the first version, followed by TN-430
TVM 430 is the cab signalling system is an evolution of the earlier TVM 300
system, which operates on similar principles. TGV lines are divided into fixed blocks
about 1500 m long. Blocks are shorter than a trains braking distance, so a braking
sequence takes place over four blocks. This relatively frequent subdivision allows to
run trains shorter head ways, which increases the capacity of a high speed line without
placing additional requirements on the braking performance of the trains. The head
ways means the time between two successive trains.

Track Capacity
The terms track capacity or line capacity or sectional capacity are used to indicate the
maximum number of trains that can be run on any given length of track per day. In
actual practice, the track capacity is limited from safety considerations, signalling and
control systems provided, speed of trains, etc. The maximum " number of trains
which can be handled in a yard per day is known as the terminal capacity.

3.3. 5 Interlocking of Signals

The interlocking is defined as the mechanical relationships established between
various levers operating the signals and the points through mechanical or electrical
agencies such effects are not at all possible in that contrary the working of the signal
mechanism.
Principles of interlocking
The three essential principles of interlocking are given here
i. It shall be impossible to lower a signal for an approaching train unless the line to
which it relates is properly set and locked and conversely, when the signal is
lowered, it shall be impossible to unlock or reverse the points.
ii. It shall the be impossible for loose wagons from any part of yard to obstruct the
line which is prepared for an expected been train after the signals relating to that line
have been lowered
iii. It shall be impossible to lower the signals for admission of trains from opposite or
converging directions to the same line at the same time
Details of a simple interlocking is given in Figure 3.76

. CE 407 Transportation Engineering II

52
 MEA Engineering College
_____________________________________________________________________________________________

Figure 3.76 Interlocking

Figure shows a single line station with a loop and siding
Following conditions will have to be satisfied:
(i) The routing signal will be so interlocked with the points that the loop signal cannot
be lowered when points are set for the main line and conversely, it will be so
interlocked with the facing points that the main signal cannot be lowered when the
points are set for the loop
(ii) The down outer signal will be so interlocked with routing signal that it cannot be
lowered until one of is first lowered.
(iii) When the facing points are set for the main line and home and outer signals are
lowered, the warner signal cannot be lowered unless the trailing points are also set
and locked for the main line.
(iv) The trap points are set against the dead end when signals are lowered for an
approaching train either to the main line or loop line.
(v) The up and down home signals will be so interlocked when one of them is
lowered, the other cannot be lowered
(vi) The corresponding conditions for up trains will to be satisfied.

. CE 407 Transportation Engineering II

53