Railway engineering

1. TOPIC : FACTOR IN SELECTION OF
GOOD ALIGNMENT IN RAILWAY
NAME : ABHIJIT SAHA
ROLL NO : 26901321038
REG NO :
212690101320001(2021-2022)
SEM :07
DEPT : CIVIL ENGINEERING
YEAR : 4TH SUB : RAILWAY &
AIRPORT
ENGINEERING (CE(PE)-705A)
ASSESMENT : CA :1

2. CONTENTS
Need for a
new railway
line
Track
Alignment
1.Importance of
a good alignment
2. Basic
Requirements
3.Selection of
good alignment
4.Mountain
Railways and
Rack railways
Conclusion
Introduction

3. INTRODUCTION
• Transportation is regarded as an index of
economic, social and commercial progress of
the country.
• Where, in various modes of transportation,
railways are cheap, fast, reliable and safe.
• To make the above advantages of railways to
be true, it is needed to align the railway track
with due consideration.
• The proper alignment of the tracks for the
above advantages are discussed here.

4. TRACK ALIGNMENT
• Giving direction and position to the centre line
of the proposed railway track on ground.
• Horizontal Alignment – straight path, its
width, deviations in width and horizontal
curves.
• Vertical Alignment – changes in gradients and
vertical curves

5. NEED FOR A NEW RAILWAY
LINE
• Strategic Reasons: for quick and easy
movement of defence forces in times of war
threat.
• Political Reasons: for political needs
• Development of backward areas: to develop
and foster development of under developed
and developing areas

6. Need for a new railway line
(Contd.,)
• To connect new trade centres: connecting new
trade centres helps in transfer of goods quicker and
facilitate their development.
• To shorten existing rail link: Short route is
economical, faster movement of goods and
passengers.
• To meet traffic requirements: doubling the
existing routes to meet heavy traffic (few cases)
• Conversion of Gauge: Recently all Meter Gauges
(MG) are converted to Broad Gauges (BG), which
may require new railway lines.

7. BASIC REQUIREMENTS OF
GOOD ALIGNMENT
An ideal alignment should fulfil the following
requirements:
Purpose of the track: In general railway
serves for the following purposes:
1. Transportation: to carry passenger and
goods traffic
2. Political and Strategic: for defence purpose
and political reasons

8. 3. Linking of centres: linking two important
stations or trade centres
4. To open new tracks: new tracks for the land
whose resources are not yet tapped
5. Shortening of existing track: Short route is
economical, faster movement of goods and
passengers.

9. Feasibility: Proposed track should meet all the
technical requirements and general planning of the
country.
Economy: Economy of the track can be achieved by
considering the factors like shortest possible route,
minimum initial construction cost, minimum
maintenance cost and minimum operating cost.
Safety: Accidents should be minimum. This can be
achieved by having due considerations on curves,
gradients, stability of natural slopes and
embankments.
Aesthetic aspects: travel should be comfortable and
pleasant.

10. FACTORS IN SELECTION OF
A GOOD ALIGNMENT
• The direct route is the shortest route which is also
the most economical route. But practically it will be
impossible to connect two points by direct route.
• It may be due to intermediate obstructions, steep
gradients, etc.,
• An alignment may be economical in initial cost, but
maintenance and operational cost may increase.
• Hence the requirements cannot be satisfied
simultaneously.

11. For satisfying the requirements the following factors
are to be considered in selection of good track
alignment.
Obligatory points
Position, amount and type of traffic
Gauge selection
Geometric standards
Topography of the country
Economic considerations
Other considerations
FACTORS IN SELECTION OF
A GOOD ALIGNMENT
(Contd.,)

12. I. Obligatory Points
• They can be classified in to two categories:
points through which the track should pass
and points through which the track should
not pass.
Points through which the track should pass:
 Important cities and towns
 Major bridges and River Crossings
 Hill passes (or) saddles
 Site for tunnels

13. Points through which the track should not
pass:
 Acquisition of costly land – results in heavy
compensation
 Religious places – they are protected by law
 Areas liable to flooding – water logged areas,
marshy areas, cutting in snow fall, etc.
With the following figure these can be explained.

14. Obligatory Points

15. II. Traffic – its position,
nature and amount
• Position of traffic sources gives control points for
general alignment
• Nature of traffic and potential volume of traffic
(passenger and goods), govern the type of
construction. General considerations are:
• Traffic varies as square of population
• Freight earnings are more than passenger earnings
• For a new alignment – influence area up to width
of 15km on either side and increased to 25km
after few years.

16. III. Gauge Selection
What is Gauge?
Gauge of a railway track is defined as the clear
distance between the inner or running faces of the
two track rails.

17. The following are the types of gauges used in
India:
Types of Gauge Gauge Width
Standard Gauge/ Broad
Gauge (BG)
1.67m
Meter Gauge (MG) 1.00m
Narrow Gauge (NG) 0.762m
Feeder Track Gauge/ Light
Gauge (LG)
0.610m

18. How to select a gauge? – Factors governing
Gauge selection:
1. Cost of construction
2. Volume and nature of traffic
3. Development of the areas
4. Physical features of the country
5. Speed of movement

19. DISADVANTAGES OF MULTI GAUGE
SYSTEM:
🙧 Inconvenience to passengers
🙧 Difficulty in trans-shipment of goods
🙧 Inefficient use of rolling stock
🙧 Hindrance to fast movement of goods and passenger
traffic
🙧 Additional facilities at station yards
🙧 Difficulties in balanced economic growth
🙧 Difficulties in future gauge conversion projects
“The above difficulties can be overcome by adopting a
uniform gauging system”

20. IV. Geometric Standards
The following geometric elements are to be considered
which would give economical combination of construction
and operating costs.
 Gradients, speed, loading and method of traction used
 Ruling gradient and minimum permissible radius of
curve
 Curve should have maximum possible radii – economical
 Reverse curves – long length of straight portion to be
provided (min. 36m)
 At stations and bridges – curves to be avoided
 Use of steep gradients – high operating costs

21. V. Topography of the
country
If the topography of the country is such a way
that, if steeper gradients are unavoidable, then
special ways to reduce the rate and cost of high
gradients are need to be adopted.
For alignment, topography can be classified as:
 Valley alignment
 Cross country alignment
 Mountain alignment

22. VALLEY ALIGNMENT
• Has no problems
• If two control points lie in the same valley, the engineer
should choose a straight line between the terminal
points with a uniform rate of gradient.
• The ends having steeper gradients can be further
negotiated by some other development.

23. CROSS COUNTRY ALIGNMENT
• This alignment crosses two or more streams/ water
sheds of different sizes.
• Uniform gradient is not possible, because the rail
levels are so high that there are no appreciable sags or
summits between the bridges.
• Hence the routes in this alignment have sags in
succession.
• Lowest saddles or tunnels form the obligatory points

24. MOUNTAIN ALIGNMENT
 It is best when accompanied by tunnelling.
 The length of the alignment is first increased between
the two extreme ends of elevation so as to limit the
gradient maximum up to the ruling gradient.
 This can be accomplished by the following special
ways:
 Zigzag development
 Switch Back development
 Spirals or complete loops development

25. Z
I
G
Z
A
G
A
L
I
G
N
M
E
N
T

26. SWITCH BACKALIGNMENT

27. BRIDGE SPIRALS

28. TUNNELSPIRAL

29. Mountain Alignment (Contd.,)
• If the gradients are less than 3%, then no problems
will arise and normal railways can be provided.
• But, if the gradients are more than 3%, special care
must be taken as said above.
• If the gradients are more than 6%, a central rack rail
has to be provided in between the two conventional
parallel rails.

30. Mountain Alignment (Contd.,)
RACK RAILS
• In case of very steep gradients, it becomes difficult for
the locomotive to pull the train load and hence the
train may slide down or slip back along the downward
gradient.
• The rack railway system consists of three rails, i.e.
two conventional rails and one extra toothed rail in
middle.
• There are various systems existing in the Indian
Railways like: Fell System, Riggenbach system and
Abt System.

31. THE FELL SYSTEM:
The Fell System was developed in 1860’s.
It uses a central raised toothed rail, in addition to the
two parallel rails.
These rails are braked by shoes pressing horizontally
on to the central rail, as well as by means of normal
running wheels.
For traction the locomotives are provided with
auxiliary engines powering the wheels that clamp onto
the third rail.
Brazil, France and New Zealand are the only countries
that have lines with the Fell System.

32. THE REIGGENBACH RACK SYSTEM:
• Invented by Niklaus Reiggenbach.
• It was given French patent in 1863.
• In this the gear teeth where in the form of rollers
arranged in the form of rungs of a ladder between two
L – shaped wrought iron rails.
• Fixed ladder rack was more complex and difficult to
build.

33. THE ABT SYSTEM:
• TheAbt System was devised by RomanAbt, a Swiss
Locomotive Engineer in early 1880’s.
• It overcame the limitations of The Reiggenbach system.
• Designed using solid bars having vertical teeth machined
to them.
• Two or three bars were placed in the middle of the rails.
They ensure that the pinions in the locomotive driving
wheels are constantly engaged with the track.
• First used in Harzbahn in Germany, opened in 1885.
• In India, a distance of about 20km from the ghat at Kallar
to Coonoor on Nigiri Railway, is constructed at a uniform
slope of 1 in 12 ½ and is being operated on the Abt
System

34. THEABT SYSTEM

35. Central Toothed Rail

36. RACK RAIL
ARRANGMENT
AFTER
KALLAR,
NILGIRI
RAILWAYS

37. VI. Economic Considerations
• Along with above factors, the alignment should be
economical also.
• The best alignment is the one which gives the
maximum annual return (r) which is given by the
formula:
r =
i.e. r = (R – E)/ l
This shows that for r to be maximum, proper selection
of route and increasing the annual returns by sound
track construction is to be considered.

38. VII. Other Considerations
1) Geological considerations Alignment
should be on good soil, free of slips or slides, not on
rocky soil.
2) Effect of flood and climate
Avoiding water logged areas.
Stations should be located on outside of the city or town
and on a level surface.
If possible track should pass through proximity of quarries
– source for ballasts are nearer.
If possible track should pass nearer to a village for cheap
labours.

39. CONCLUSION
• Giving direction and position to the centre line of the
proposed railway track on ground, is called as track
alignment.
• The need for new track may be due to strategic,
political reasons, to develop backward areas, to
connect new trade centres and to shorten existing
railway track.
• The factors affecting a good alignment are obligatory
points; amount, type and nature of traffic; topography
of the country; geometric; economic and other
considerations.

40. REFERENCES
1. Saxena, S.C and Arora, S.P. “A Text Book of
Railway Engineering”, Dhanpat Rai
Publications, New Delhi, 8th edition, 2015.
2. Chandra, Satish and Agarwal, M. M.
“Railway Engineering”, Oxford University
Press, New Delhi, 2nd edition, 2013.
3. Images from Google Images