Railway and Airport Engineering

Transportation Engineering-II
RAILWAY ENGINEERING AIRPORT ENGINEERING

The branch of Civil Engineering
which deals with the design,
construction and maintenance of
the railway tracks for safe and
efficient movements of trains is
called Railway Engineering

In a permanent way, rails are joined either by
welding or by using fish plates and are fixed with
sleepers by using different types of fastenings.
Sleepers are properly placed and packed with
ballast. Ballast is placed in the prepared subgrade
called formation.

Ideal Requirements of Permanent way
• Gauge should be correct and uniform.
• In a straight track, two rails, must be at same level.
• The track should have enough lateral strength so that alignment
is maintained.
• The gradients should be uniform.
• Drainage system must be perfect for enhancing safety and
durability of tracks.
• The radii and super-elevation on curves should be properly
designed.
• Joints including points and crossings which are regarded to be
the weakest points of the railway track should be properly
designed and maintained.
• There should be adequate provision for easy renewals and
replacements.
• The track should be strong, low in initial cost, as well as
maintenance cost.

Rail Gauge
• Rail gauge is the distance from the inside of
one rail on a railroad track to the inside of the
other.

TYPES OF GAUGES PREVALENT IN
INDIA
The different gauges prevalent in India are of
the following these types :-
• Broad gauge (1676 mm)
• Metre gauge (1000 mm)
• Narrow gauge (762 mm & 610 mm)

Choice of Gauge
The choice of gauge is very limited, as each
country has a fixed gauge and all new railway
lines are constructed to adhere to the standard
gauge. However, the following factors
theoretically influence the choice of the gauge:-
• Cost consideration
• Traffic Consideration
• Physical Features of the Country
• Uniformity of Gauge

Uniformity of gauge
Gauge to be used in a particular country should be uniform throughout as far
as possible because it will avoid many difficulties experienced in a non-
uniform system, and will result in following advantages:-
• The delay, cost and hardship in trans-shipping passengers and goods from
the vehicles of one gauge to another is avoided.
• Difficulties in loading and unloading are avoided & labour expenses are
saved.
• As the trans-shipping is not required, there is no breakage of goods.
• Possibility of thefts and misplacement while changing from one vehicle to
another are avoided.
• Labour strikes, etc do not affect the service and operation of trains.
• Surplus wagons of one gauge cannot be used on another gauge. This
problem will not arise if gauge is uniform.
• During military movement, no time is wasted in changing personal and
equipment from one vehicle to another, if gauge is uniform.
• Locomotives can be used on all the tracks if a uniform type of gauge is
adopted.

Basic Requirements of an Ideal
Alignment
• Purpose of the New Railway Line
• Integrated Development
• Economic Considerations
• Maximum Safety and Comfort
• Aesthetic Considerations

Selection of a Good Alignment
Normally, a direct straight route connecting two points is the
shortest and most economical route for a railway line, but there
are practical problems and other compulsions which necessitate
deviation from this route. The various factors involved is the
selection of a good alignment for a railway line are given below:-
• Choice of Gauge
• Obligatory or Controlling Points
• Important Cities and Towns
• Major Bridges and river Crossing
• Existing Passes and saddle in Hilly Terrain
• Site for Tunnels
• Topography of the country
• Plane Alignment
• Valley Alignment

The rolled steel sections laid end to end in
two parallel lines over sleepers to form a
railway track are known as Rails.

Double headed rails
These rails indicate the early stage of
development. It mainly consists of 3 parts
:- Upper table, Web, Lower table. Both the
upper table and lower tables were
identical. When upper table gets worn out,
then the rails can be inverted and reused.
This type of rails is practically out of use in
Indian Railways.

Bull Headed Rails
The rail section whose head dimensions are
more than that of their foot is called bull-
headed rails. In this type of rail, the head is
made little thicker and stronger than the
lower part by adding more metal to it. This rail
s also require chairs for holding them in
position. Bull-headed rails are especially used
for making points and crossings.

MERITS:
• B.H. Rails keep better alignment and provide
smoother and stronger track.
• These rails provide longer life to wooden
sleepers and hence renewal of track is easy.
• These rails are easily removed from sleepers
and hence renewal of track is easy.
DEMERITS:
• B. H. Rails requires additional cost of iron chairs.
• These rails require heavy maintenance cost.
• B.H. Rails are of less strength and stiffness

Flat Footed Rails
The rail sections having their foot rolled to flat
are called flat-footed or Vignoles rails. The
foot is spread out to form a base. It distributes
the train load over a large number of sleepers
and is more cheaper than Bull Headed Rails.
These rails are most commonly used in India.
About 90% of the railway tracks in the world
are laid with this form of rails.

MERITS:
• Flat footed rails have more strength and
stiffness.
• These rails require less number of fastenings.
• The maintenance cost of the track formed with
F.F rails is less.
DEMERITS:
• The fittings get loosened more frequently.
• These rails are not easily removed and hence
renewal of track becomes difficult.
• It is difficult to manufacture points and
crossings using these rails.

Sleepers are members generally laid transverse to the rails on
which the rails are supported and fixed to transfer the load
from rails to the ballast and subgrade below.

FUNCTIONS OF SLEEPERS:
• To hold the rails to proper gauge.
• To transfer the loads from rails to the ballast.
• To support and fix the rails in proper position.
• To keep the rails at a proper level in straight
tracks and at proper super-elevation on curves.
• To provide elastic medium between the rails and
the ballast
• To provide stability to the permanent way on the
whole.

REQUIREMENTS OF GOOD SLEEPERS:
• The sleepers should be sufficiently strong to act as a beam under
loads.
• The sleepers should be economical.
• They should maintain correct gauge.
• They should provide sufficient bearing area for the rail.
• The sleepers should have sufficient weight for stability.
• Sleepers should facilitate easy fixing and take out of rails without
disturbing them.
• They should facilitate easy removal and replacement of ballast.
• They should not be pushed out easily of their position in any
direction under maximum forces of the moving trains.
• They should be able to resist impact and vibrations of moving trains.
They should be suitable for each type of ballast.
• If track-circuiting is done, it should be possible to insulate them from
the rails

TYPES OF SLEEPERS:
• WOODEN SLEEPERS
• METAL SLEEPERS (Cast Iron sleepers/ Steel
sleepers)
• CONCRETE SLEEPERS (RCC sleepers/ Pre-
stressed concrete sleepers)

Wooden sleepers
Wooden sleepers are regarded to be the best as
they fulfil almost all the requirements of an ideal
sleeper. The life of wooden sleepers depends
upon their ability to resist wear, decay, attack by
vermin, quality of timber used.

Advantages of wooden sleepers
• Timber is easily available in all parts of India.
• Fittings of wooden sleepers are few and simple
in design.
• These sleepers are able to resist the shocks and
vibrations due to heavy moving loads and
hence give less noisy track.
• Wooden sleepers are easy to lay, relay, pack,
lift and maintain.
• These sleepers are suitable for all types of
ballast.
• Wooden sleepers are economical.

Disadvantages
• These sleepers are subjected to wear, decay,
attack by white ants, spike killing, cracking, etc.
• It is difficult to maintain gauge in case of
wooden sleepers.
• Track is easily disturbed i.e. Alignment
maintenance is difficult.
• Maintenance of wooden sleepers is highest as
compare to other sleepers.
• Wooden sleepers have got minimum life (12-
15 yrs) as compare to other type of sleepers.

Metal sleepers
Due to growing scarcity of wooden sleepers,
their high cost and short life, metal sleepers are
now highly adopted in India.

Advantages of Metal Sleepers
• Metal sleepers are uniform in strength and
composition.
• The performance of fittings is better and hence
less creep occurs.
• Metal sleepers are economical and
maintenance is easier.
• They are not susceptible to fire hazards.
• They have a simple process of manufacturing.
• They have a good scrap value.
• Gauges are easily adjusted and maintained in
case of metal sleepers.

Disadvantages
• Fittings are greater on number.
• More ballast is required than other type of
sleepers.
• Prone to corrosion.
• Only suitable for stone ballast.
• Metal sleepers are unsuitable for bridges,
level crossings and in case of points and
crossings.

Concrete sleepers
They are made of strong homogenous material,
impervious to effects of moisture and is unaffected
by the chemical attack of atmospheric gases.

Advantages of R.C.C. Sleepers:
• Concrete sleepers have a long life, generally 40 to 60
years.
• These are free from natural decay and attack by
insects’ etc.
• These sleepers require fewer fittings.
• Track circuiting is possible in these sleepers.
• These sleepers provide more lateral and longitudinal
rigidity as compared to other sleepers.
• The maintenance cost is low.
• Due to higher elastic modulus, these can withstand the
stresses due to fast-moving trains.

Disadvantages:
• Due to heavyweight, handling and
transportation of these sleepers are Difficult.
• If not handled properly, the chance of
breaking is more.
• The renewal of track laid with these sleepers is
difficult.
• The scrap value is nil.

Pre-stressed Concrete Sleepers:
Pre-stressed concrete sleepers are nowadays
extensively used in Indian Railways. These
sleepers have high initial cost but are very
cheap in long run due to their long life. In these
sleepers, high tension steel wires are used.
These wires are stretched by hydraulic jack to
give necessary tension in the wires. The
concrete is then put under a very high initial
compression. These sleepers are heavily
damaged in case of derailment or accidents of
trains.

Spacing of sleepers
• The space between two adjacent sleepers determine the
effective span of the rail over the sleepers. The spacing of
sleepers therefore, in a track depends on the axle load
which the track is expected to carry and lateral thrust of
locomotive to which it is satisfied.
• The number of sleepers per rail length is defined as
Sleeper Density. Since sleepers provide lateral stability to
the tracks, so more the number of sleepers more is the
lateral stability.
• The number of sleepers however cannot be increased
indefinitely as the certain minimum space between the
sleepers is required for packing of ballast. In India this
minimum distance is 30.5 cms to 35.5 cms.

Sleeper density
• Sleeper density is the number of sleepers
Per rail length. It is specified as (M+x) or
(N+x), where M or N is the length of the rail
in meters and x is a number that varies
according to factors such as axle load,
speed, type & section of the rail etc.
• It varies in India from M+4 to M+7 for main
tracks.

Ballast is a granular material usually broken stone or brick
placed and packed below and around the sleepers to
transmit load from sleeper to formation and at the same
time allowing drainage of the track.

FUNCTIONS OF BALLAST:
• To hold the sleepers in position and
preventing the lateral and longitudinal
movement.
• To distribute the axle load uniform from
sleepers to a large area of the formation.
• To provide elasticity to the track. It acts as
elastic mat between subgrade and sleepers.
• To provide easy means of maintaining the
correct levels of the rails in a track.
• To drain rainwater from the track.
• To prevent the growth of weeds inside the
track

CHARACTERISTICS OF GOOD BALLAST:
• It should have sufficient strength to resist crushing under heavy
loads of moving trains.
• It should be durable enough to resist abrasion and weathering
action.
• It should have a rough and angular surface so as to provide good
lateral and longitudinal stability to the sleepers.
• It should have good workability so that it can be easily spread of
formation.
• It should be cheaply available in sufficient quantity near and along
the track
It should not make the track dusty or muddy to its crushing to
powder under wheel loads.
• It should allow for easy and quick drainage of the track.
• It should not have any chemical action on metal sleepers and rails.

Capacity of a railway track
• Track Capacity is the hourly capacity of the track
to handle trains safely or in other words, it is the
number of trains that can be run safely on a track
per hour.
Track Capacity can be Increased:-
• By achieving faster movement of trains on a
track.
• By decreasing the distance between successive
trains.

Track Fixtures And Fastenings
• Fixtures and fastenings are fitting to require
for joining of rails end to end and also for
fixing the rails to sleepers on a track.

FUNCTIONS OF FIXTURES AND
FASTENINGS
• To join the rails end to end to form full length
of track
• To fix the rails to sleepers.
• To maintain the correct alignment of the track.
• To provide proper expansion gap between
rails.
• To maintain the required tilt of rails.
• To set the points and crossings in the proper
position.

TYPES OF FIXTURES AND FASTENING:
• Fish plates
• Bearing plates
• Spikes
• Chairs
• Bolts
• Keys
• Anti-creepers

Fish plate
Fish plates are used in the rail joints to maintain the
continuity of the rails and to allow for any expansion or
contraction of rails caused by temperature variations. At one
particular joint there is 2 fish plates and 4 bolts and 4 nuts.

Rail Joints
• Supported Rail Joint
• Suspended Rail Joint
• Bridge Joint
• Base Joint
• Welded Rail Joint
• Staggered or Broken Joint
• Square or Even Joint
• Compromise Joint
• Insulated Joint
• Expansion Joint

Insulated Joint Expansion Joint

Creep of Rails
• Creep is defined as the longitudinal movement
of the rail with respect to the sleepers.

Indications of creep
• Closing of successive expansion spaces at rail
joints in the direction of creep and opening
out of joints at the point where the creep
starts.
• Marks on the rail flanges and webs made by
spike heads by scrapping or scratching at the
rail slide.

Disadvantages of creep
• Sleepers move out of position thereby the rail
gauge.
• Position of points and crossings are disturbed.
• Interlocking mechanism gets disturbed.

Remedies of prevention of creep
• Pulling back the rails:-
If the creep is distinctively visible, the remedy is to pull back
the rails. For doing this, first inspect the track, note the
extent of pulling back and determine the point from which
to begin.
• Provision of Anchors and Anti-creepers:-
Anchors are fastened to the foot of the rails and are in
absolute content with the side of sleeper on the side
opposite to the direction of the creep.
• Use of steel sleepers:-
sleepers should be of such a type with such fittings that
they prevent the rail from creeping on them. Steel trough
sleepers are best for this purpose.

Coning of wheels
The tread or rim of the railway vehicles are
not made flat but are sloped and this sloping
surface along the circumference forms part
of a cone (with a slope of about 1 in 20). This
is known as coning of wheels.

Theory of coning
On a level track, as soon as the axle moves
towards one rail, the diameter of the wheel
tread over the rail increases, while It
decreases over the other rail. This prevents
to further movement And axle retreats back
to its original position (with equal dia or
both rails and equal pressure on both rails).

Advantages of coning of wheels
• It helps the vehicle to negotiate curves
smoothly.
• It reduces wear and tear of wheel flanges.
• To keep the train just in central position in a
level track.
• To prevent wheels from slipping to some
extent.

Disadvantages
• The pressure of the horizontal component of
the force near the near edge of rails has the
tendency to wear the rail quickly.
• If no base plates are provided, sleepers under
the outer edge of the rails may get damaged.

Adzing of sleepers
A groove (having angle 1 in 20) is being cut
on the top of the sleeper. The rail is being
seated into this groove in such a manner
that it remains fixed in this location. This
sort of angle making in sleepers so as to
seat the rail is known as Adzing of sleepers.

Gradient:
The gradient is the rate of rising or fall off the
track. It is expressed as the ratio of vertical
distance to horizontal distance or as the
percentage of rising or fall. If any track rises 1 m
100 m horizontal length, its gradient is
expressed as 1 m 100 or 1 percent. If another
track falls by 1 m 50 m length, its gradient is 1
in 50 or 2 percent.
Gradient design should be such as to provide
maximum efficiency in the traffic operation
with maximum safety at reasonable cost.

Gradients are provided to the formation of rail
track to serve the following purpose:
• To reduce the cost of earthwork
• To provide uniform rate or fall as far as practicable.
• To reach the stations situated at different elevations.
• To drain off rainwater
Factors which affect the selection of gradient are the
following:
• Nature of the ground
• Safety required
• Drainage required
• Total height to be covered
• Hauling capacity of railway engines

Types of Gradient:
• Ruling gradient
• Momentum gradient
• Pusher gradient
• Station yard gradient

Ruling Gradient:
• The ruling gradient is the maximum gradient to which the track
may be laid in a particular section. It depends on the load of the
train and additional power of the locomotive. The ruling
gradients adopted:
• In plains – 1 in 150 to 1 in 200
• In Hilly tracks – 1 in 100 to 1 in 150
Momentum Gradient:
• Gradient which is steeper than ruling gradient and where the
advantage of momentum is utilized is known as momentum
gradient. A train gets momentum when moving in down-
gradient and this momentum can be utilized for up-gradient. A
train while coming down a gradient gains sufficient momentum.
This momentum gives additional kinetic energy to the moving
train which would help the train to rise a steeper gradient than
the ruling gradient for a certain length of the track. This rising
gradient is called momentum gradient. In such gradients, no
signals are provided to stop the train.

Pusher Gradient:
• Pusher gradient is the gradient where an extra engine is
required to push the train. These are steeper gradient than
ruling gradient and are provided at certain places of mountains
to avoid heavy cutting or to reduce the length of the track. A
pusher gradient of 1 in 37 on Western Ghats with B.G. track is
provided. On Darjeeling Railway with N.G. track, a ruling
gradient of 1 in 25 is provided.
Station yard Gradient:
• Station yard gradient is the minimum gradient provided in
station yard for easy draining of rainwater. Gradients are avoided
as far as possible in station yard due to following reasons
• In station yard, Bogies standing on gradients may start moving
due to heavy wind and may cause an accident.
• The locomotives will require an extra force of pull the train on
gradients at the time of starting the trains.
• In station yards, the maximum limit of the gradient is fixed as 1
in 400 and minimum gradient recommended is 1 in 1000 for
easy drainage of rainwater.

GRADE COMPENSATION OF CURVES:
Grade compensation on curves is the reduction
in gradient on a curved portion of a track. On
curves, the extra pull is required to pull the
train due to more tractive resistance.
Therefore, if gradients are to be provided on
curves some compensation should be given in
ruling gradients to overcome the increased
tractive resistance to a certain limit and to pull
the trains with the same speed. It is expressed
as the percentage per degree of curve. The
grade compensation provided on
B.G. curves – 0.04percent /degree.

Radius & degree of curve
• The main curved portion of a railway track is
kept circular i.e. The radius at every point of
the curve is same. The radius of the railway
curve can be represented by the degree of the
curve.
• The degree of the curve is defined as the
angle subtended at the centre of the curve by
an arc or chord of length 100ft (30.5m)

Superelevation in rails:
Superelevation is the raised elevation of the outer
rail above the inner rail at a horizontal curve. It is
denoted by ‘e’. When a vehicle moves on the curve it
is subjected to a centrifugal force. The centrifugal
force exerts a horizontal force on the outer rail and
the weight on the outer rail increases. This
horizontal force and uneven load on rails will cause
the derailment. This centrifugal force can be
countered by introducing the centripetal force by
raising the outer rail with respect to the inner rail.
This raising of outer rail with respect to inner rail is
known as ‘superelevation’ or ‘canting’.

Objects of Providing
Superelevation:
• To introduce centripetal force to counteract
the centrifugal force to avoid derailment
and reduce the side wear of rails.
• To distribute the wheel loads equally on the
two rails. This reduces the top wear of rails
and results in saving of maintenance cost.
• To ensure the comfortable ride for
passengers and safe movements of goods

Cant Deficiency:
• Cant deficiency is the difference between the actual cant
provided and equilibrium cant necessary for the maximum
permissible speed on a curve. Cant deficiency should be as low
as possible and is limited due to following reasons:
• Higher discomfort to passengers due to higher cant deficiency
• Higher cant deficiency results in higher unbalanced centrifugal
force and hence extra pressure and lateral thrust on the outer
rails, requiring strong track and more fastening for stability.
• Side wear and creep of outer rails of the track are more due to
higher cant deficiency. Maximum values of cant deficiency as
prescribed on Indian Railways On BG
For speeds up to 100kmph = 76mm
For speeds up to higher than 100kmph = 100mm

NEGATIVE CANT:
On curves, branch line meets the main line at
certain places. The outer rail of the main line of
curves meets the inner rail of the branch line. As
the superelevation is provided on the main line,
the outer rail of the main line is at the higher
level than the inner rail. The inner rail of branch
line will have to be kept at the higher level than
inner rail. But here as the outer rail in branch
line is at lower level than inner rail, the
superelevation is known as ‘Negative
superelevation’ or ‘Negative cant’.

Equilibrium speed
• When the speed of a vehicle negotiating a
curved track is such that the resultant force of
the weight of the vehicle and the radial
acceleration is perpendicular to the plane of
the rails, the vehicle is not subjected to any
unbalanced radial acceleration and is said to
be in equilibrium. This particular speed is
called the equilibrium speed.

Maximum permissible speed on the curve
The maximum permissible speed on a curve is taken as the
minimum value of the speed calculated by the following
methods:-
• Maximum sanctioned speed of the section:- This is the
maximum speed authorised by additional commissioner of the
Railway based upon the track condition and standards of
signalling and interlocking.
• Safe speed over the curve:- This is the speed calculated by
Martin’s Formulae of safe speeds for different gauges.
• Speed based upon the consideration of the super-elevation:-
This is calculated for Formula of super-elevation where the
value of super-elevation is sum of full amount of cant deficiency
and the actual super-elevation.

necessity of geometric design
Most of the trains derailment are due to:-
• Track Defects
• Vehicular Defects
• Operational Defects
The civil engineers are mainly concerned
with the track defects and how to remove
these defects so that no derailment takes
place.

Track defects
• Improper Gradients
• Defective Gauge
• Improper Super-elevation
• Improper Radius of Curve
• Improper design Speed
• Unequal distribution of loads on two rails
• Improper Points & Crossings

Transition curves
• As soon as a train commences motion on a circular curve from
a straight line track, it is subjected to a sudden centrifugal
force, which not only causes discomfort to the passengers, but
also distorts the track alignment and affects the stability of the
rolling stock. In order to smoothen the shift from the straight
line to the curve, transition curves are provided on either side
of the circular curve so that the centrifugal force is built up
gradually as the super-elevation slowly runs out at a uniform
rate.
• A transition curve is, therefore, the cure for an uncomfortable
ride, in which the degree of the curvature and the gain of
super-elevation are uniform throughout its length, starting
from zero at the tangent point to the specified value at the
circular curve.

Vertical curves
• Summit curves
• Sag or Valley curves
• Whenever, there is a change in the gradient of the track, an angle is
formed at the junction of the gradients. This vertical kink at the
junction is smoothened by the use of curves, so that bad lurching is
not experienced. The effects of change of gradient cause variation in
the draw bar pull of the locomotive.
• When the train climbs a certain upgrade at a uniform speed and
passes over the summit of the curve, an acceleration begins to act
upon it and makes the train to move faster and increases the draw bar
pull behind each vehicle, causing a variation in the tension in the
couplings.
• When the train passes over the sag, the front of the train ascends an
upgrade while rear vehicles tend to compress the couplings and
buffers, and when the whole train has passed the sag, the couplings
are again in tension causing a jerk. Due to above reasons, it is essential
to introduce a vertical curve at each sag and at each summit or apex.

Points & Crossings
• Points and crossings provide flexibility of
movement by connecting one line to
another according to requirements.
• They also help for imposing restrictions over
turnouts which necessarily retard the
movements.
• From safety aspect, it is also important as
points and crossings are weak kinks or
points in the track and vehicles are
susceptible to derailments at these places.

Crossing:
The crossing is a device provided at the
intersection of two running rails to permit the
wheel flanges, moving along one to pass across
the other.

Component Parts of a Crossing:
• A Vee piece
• A point rail
• A splice rail
• Two check rails
• Two wing rails
• Heel blocks at throat, nose, and heel of
crossing
• Chairs at crossing, at toe and at heel

REQUIREMENTS OF IDEAL CROSSING:
• Crossing assembly should be rigid enough to
withstand severe vibrations.
• Wing rails and nose crossing should be able to
resist heavy wear due to movement of wheels,
hence should be manufactured of special
steel(alloy steel)
• The nose of crossing should have adequate
thickness to take all stresses acting on the
crossing.

Types Of Crossing:
• On the basis of shape of crossing
• square crossing
• Acute angle or V-crossing or Frog
• Obtuse angle or Diamond crossing
• On the basis of assembly of crossing
• Ramped crossing
• Spring or movable crossing

Square Crossing:
Square Crossing is formed when two straight tracks of
same or different gauge, cross each other at right
angles. This type of crossing should be avoided on
main lines because of heavy wear of rails.

Acute Angle Crossing:
Acute angle crossing is formed when left-hand
rail of one track crosses right-hand rail of
another track at an acute angle or vice versa.
This type of crossing consists of a pair of wing
rails, a pair of check rail and a splice rail. This
crossing is widely used. This is also called V-
crossing or frog.

Obtuse Angle Crossing:
The obtuse crossing is formed when left-hand
rail of one track crosses right-hand rail of
another track at an obtuse angle or vice versa.
This type of crossing consists mainly of two
acute and two obtuse angle crossings. This is
also called Diamond crossing.

Turnout:
Turnout is an arrangement of points and
crossings with lead rails by which trains may
be diverted from one track to another
moving in the facing direction. A turnout is
left handed or right handed as the train
taking the turnout in the facing direction is
diverted to the left or right of the main line.

Component parts of a turnout and their
functions:
A pair of tongue rails:
• The tongue rails along the stock rails in a turnout form a pair of points or
switches. The tongue rails facilitate the diversion of a train from the
main track to branch track.
A pair of Stock Rails:
• They are the main rails to which the tongue rails fit closely. The stock
rails help in the smooth working of tongue rails.
Two Check Rails:
• Check rails are provided adjacent to the lead rails, one in main track and
another in branch rack. These rails check the tendency of wheels to
climb over the crossing.
Four Lead Rails:
• Outer straight lead rail, outer curve lead rail, inner straight lead rail and
inner curve lead rail are the four lead rails provided in a turnout. The
function of these rails is to lead the track from heel of switches to the
toe of the crossing.

A Vee Crossing:
• A Vee Crossing is formed by two wing rails, a point rail, and a
splice rail. It provides gaps between the rails so that wheel
flanges pass through them without any obstruction.
Slide Chairs:
• Slide chairs are provided to support the tongue rail throughout
their length and to allow lateral movement for changing of
points.
Stretcher Bar:
• Stretcher bar connects toes of both the tongue rails so that each
tongue rail moves through the same distance while changing the
points.
A pair of Heel Blocks:
• These keep the heel ends of both the tongue rails a fixed
distance from their respective stock rails.
Switch Tie Plate:
• The function of switch tie plate is to hold the track rigidly to the
definite gauge at the toe of switches. These are provided below
the slide chairs.

KNOWLEDGE OF SIGNALLING:
Shunt signal: This is meant for signalled shunting in the interlocked station
section performed with a locomotive. The shunt signal leads movement
from one shunt signal to the next shunt or stops signal whichever falls
first on the route. When a shunt signal is mounted on the same post as
that of a running signal, both the main or shunt signal cannot be taken
off at the same time. Either the main signal shall be taken off or the
shunt signal at any one time.
Back Locking: After the train has passed the signal, it is important to put
back the signal to ‘On’ which in turn shall release entire route ahead,
which was kept locked by the signal level or approach locking circuits so
far. When a track circuit is provided ahead of the signal, the signal is
replaced back by the occupation of the track circuit. In case of
mechanical signal the reverser provided with the signal is released
putting back the signal to ‘On’ and in case of the color light signal, the
signal is put back to ‘On’ by the occupation of track circuit through
selection circuits. Occupation of this track circuit also simultaneously
initiates back locking circuits.

Track Locking:
• It is holding the points locked while it is under the wheels
of a train. Mechanically it is done by attaching a lock bar
to the facing point lock. The length of the lock bar is kept
as such to cover the maximum distance between the two
successive wheel bas3s of any vehicle. The length of lock
bar is accordingly dept to be 42 feet. The lock barf
attached to the facing point lock plunger moves to-and-
fro along with the plunger through a radial guide, due to
which the lock bar has to lift up to rail top level.
• The unlocking movement of the plunger is not possible if
a wheel is over the lock bar as the flange of the wheel
shall not allow the lock bar to be lifted to the level of rail
top. Electrically, the track locking is also provided through
track circuits in the entire point zone. The occupation of
the track circuit detects the presence of a train over the
point zone, which keeps the point locked through
selection circuits.

Classification & types of signals
Based on Operation Characteristics
• Detonating Signals:- During foggy and cloudy weather
when hand or fixed signals are not visible, detonators are
placed on the rails which explode with loud sound when
the train passes over them.
• Hand Signals:- hand signals are given either by flags fixed to
a wooden handle or by bare arms when the flags are not
available, during the daytime. During night time, lamps are
used in which movable glass slides of green, red and yellow
shades are provided.
• Fixed Signals:- They are usually of Semaphore type fixed at
place.

Based on Functional Characteristics
• Stop or Semaphore type signals
• Warner Signals
• Shunting Signals
• Coloured lights Signals
Based on Location Characteristics
• Reception Signals (Outer Signals, Home Signals)
• Departure Signals (Starter, Advanced Signals)
Based on Special Characteristics
• Repeater or co-acting Signals
• Routing Signals
• Calling Out
• Point Indicators
• Miscellaneous Signals

Coloured-light Signals
Shunting Signals
Semaphore type Signals
Detonating Signals

• Semaphore type or stop signal:- The principle of design
of this type of signal is to show the stop position of any
failure that happens to be in the apparatus. The signal
mechanism is so arranged that in the normal position it
indicates the stop position.
• Dock signal:- This signal leads the train to the dock
platform. In this case, the semaphore reception signal is
provided with a stencil-cut letter 'D' on the signal for use.
• Trap indicator:- A trap is a device fitted on the track,
which in its open position derails the vehicle that passes
over it. When the trap is closed, the vehicle passes over it
as it would over a normal track. A trap indicator reveals
whether the trap is in an 'open' or 'closed' position.

Railway station
• The selected place on a railway track where
trains are stopped for exchange of
passengers, goods and control of train
movements, are known as Railway Stations.

Purpose of railway stations
• Exchange of passengers and goods
• Control of train movement
• To enable train moving in opposite direction
for a single line track to cross each other.
• To enable the following express train to
overcome a slow moving goods train.

Site selection for railway station
• Station site should be close to the towns or village which could be
served.
• Station site should have fairly level ground.
• Site should provide good drainage facility.
• Site should have good approach to roads connecting the nearby
village or town.
• Station site should fulfil the civil as well as military requirements.
• The site should provide amenities such as drinking water, etc. the
availability of sufficient quantity of drinking water from nearby
source is very essential.
• Sufficient land area for the provision of single track or double track,
additional lines, stations, buildings, platforms, staff quarters and for
future development of stations should be available at the site.

Track Drainage
Track drainage can be defined as the interception, collection,
and disposal of water from, upon, or under the track. It is
accomplished by installing a proper surface and sub-surface
drainage system.

Need of Proper Drainage
• Settlement of Embankment
• Reduction in bearing capacity
• Failure of Embankment
• Formation of Ballast Pocket
• Shrinkage and Cracking of Bank
• Adverse affect of black cotton soil
• Formation of Slash

Airport is a facility where
passengers connect from
ground transportation to air
transportation.
Air transportation is one system
of transportation which tries to

Airport Authority of India
• Controls overall air navigation in India
• Constituted by an act of parliament and it came into being on 1st
April, 1995
• Formed by merging NAA (National Airport
• Authority) and IAAI (International Airport Authority of India)
• AAI manages 125 airports, which include 18 international
airports, 7 custom airports, 78 domestic airports and 26 civil
enclaves at defence airfields.
Functions of AAI
• Control and management of the Indian airspace extending
beyond the territory limits
• Design, development and operation of domestic and international
airports
• Construction and management of facilities

International civil aviation
organisation
• In 1944, US invited all allied nations for a conference on post war civil
aviation in the world. The result of discussion was the Chicago
Convention on civil aviation. With the signing of a treaty in December
1944, ICAO was created as an inter-governmental organisation and in
1947 it became a specialised agency in relationship with the UN.
• 52 countries signed the Chicago Convention on international civil
aviation in Chicago on 7 Dec, 1944.
• ICAO is active in infrastructure management, including communication,
navigation and surveillance/ air traffic management systems, which
employ digital technologies in order to maintain a seamless global air
traffic management system.
• ICAO also standardizes certain functions for use in the airline industry,
such as AMHS (Aeronautical Message Handling Systems). Every country
should have an accessible Aeronautical Information Publication (AIP),
based on standards defined by ICAO.

Objectives/ functions of ICAO
• Ensure the safe and orderly growth of international
civil aviation throughout the world.
• Encourage the art of aircraft design and operation for
peaceful purposes.
• Encourage the development of airways, airports and air
navigation facilities for international aviations.
• Meet the needs of the people of the world for safe,
regular, efficient, and economical air transport.
• Prevent economic waste by unreasonable competition.
• Promote safety of flight in international air navigation.
• Avoid discrimination between contracting states.

International air transport association
(IATA)
• It is a trade association of world’s airlines
consisting of 278 airlines, representing 117
countries.
• IATA supports airline activity and helps
formulate industry policy and standards.
• Safety is the number one priority for IATA.
• IATA provides consulting and training
services in many areas crucial to aviation.

Airport System Plan
The airport system plan provides both broad and specific policies, plans, and programs required to
establish a viable and integrated system of airports to meet the needs of the region. The objectives
of the system plan include:-
• The orderly and timely development of a system of airports adequate to meet present and future
aviation needs and to promote the desired pattern of regional growth relative to industrial,
employment, social, environmental, and recreational goals.
• The development of aviation to meet its role in a balanced and multimodal transportation system to
foster the overall goals of the area as reflected in the transportation system plan and comprehensive
development plan.
• The protection and enhancement of the environment through the location and expansion of
aviation facilities in a manner which avoids ecological and environmental impairment.
• The provision of the framework within which specific airport programs may be developed consistent
with the short- and long-range airport system requirements.
• The implementation of land-use and airspace plans which optimize these resources in an often
constrained environment.
• The development of long-range fiscal plans and the establishment of priorities for airport financing
within the governmental budgeting process.
• The establishment of the mechanism for the implementation of the system plan through the normal
political framework, including the necessary coordination between governmental agencies, the
involvement of both public and private aviation and non aviation interests, and compatibility with
the content, standards, and criteria of existing legislation. The airport system planning process must
be consistent with state, regional, or national goals for transportation, land use, and the
environment.

Airport Classification
• International Airports
• Custom Airports
• Model Airports
• Other Domestic Airports
• Civil Enclaves in Defence Airport

SITE SELECTION
The emphasis in airport planning is normally on the expansion and
improvement of existing airports. However if an existing airport cannot
be expanded to meet the future demand or the need for a new airport is
identified in an airport system plan, a process to select a new airport site
may be required.
• Identification
• Screening
• Operational capability
• Capacity potential
• Ground access
• Development costs
• Environmental consequences
• Compatibility with area-wide planning
• Readily accessible to the users
• Natural protection from air-raids

AIRPORT MASTER PLAN
• An airport master plan is a concept of the ultimate development of
a specific airport.
• The term development includes the entire airport area, both for
aviation and non-aviation uses, and the use of land adjacent to the
airport. It presents the development concept graphically and
contains the data and rationale upon which the plan is based.
• Master plans are prepared to support expansion and modernization
of existing airports and guide the development of new airports.
• The overall objective of the airport master plan is to provide
guidelines for future development which will satisfy aviation
demand in a financially feasible manner and be compatible with the
environment, community development, and other modes of
transportation.

IMAGINARY SURFACES
• In order to determine whether an object is an obstruction to air
navigation, several imaginary surfaces are established with relation to
the airport and to each end of a runway. The size of the imaginary
surfaces depends on the category of each runway (e.g., utility or
transport) and on the type of approach planned for that end of the
runway (e.g., visual, non precision instrument, or precision
instrument).
• Primary surface. The primary surface is a surface longitudinally
centered on a runway. When the runway is paved, the primary surface
extends 200 ft beyond each end of the runway. When the runway is
unpaved, the primary surface coincides with each end of the runway.
The elevation of the primary surface is the same as the elevation of
the nearest point on the runway centerline.
• Horizontal surface. The horizontal surface is a horizontal plane 150 ft
above the established airport elevation, the perimeter of which is
constructed by swinging arcs of specified radii from the center of each
end of the primary surface of each runway and connecting each arcs
by lines tangent to those arcs.

• Conical surface. The conical surface is a surface
extending outward and upward from the periphery of
the horizontal surface at a slope of 20 horizontal to 1
vertical for a horizontal distance of 4000 ft.
• Approach surface. The approach surface is a surface
longitudinally centered on the extended runway
centerline and extending outward and upward from
each end of a runway at a designated slope based upon
the type of available or planned approach to the
runway.
• Transitional surface. Transitional surfaces extend
outward and upward at right angles to the runway
centerline plus the runway centerline extended at a
slope of 7 to 1 from the sides of the primary surface up
to the horizontal surface and from the sides of the
approach surfaces. The width of the transitional surface
provided from each edge of the approach surface is
5000 ft.

AIRCRAFT CHARACTERISTICS
• Type of propulsion of aircraft
• Size of aircraft
• Minimum turning radius
• Minimum circling radius
• Speed of the aircraft
• Aircraft capacity
• Weight of aircraft and wheel configuration
• Jet blast
• Fuel Spillage
• Noise

Important Components of An Airport
Layout
• Runway
• Terminal Building
• Apron
• Taxiway
• Aircraft Stand
• Hanger
• Control Tower
• Parking

RUNWAY
A runway is a rectangular area on the airport surface
prepared for the takeoff and landing of aircraft. An
airport may have one runway or several runways
which are sited, oriented, and configured in a
manner to provide for the safe and efficient use of
the airport under a variety of conditions. Several of
the factors which affect the location, orientation,
and number of runways at an airport include local
weather conditions, particularly wind distribution
and visibility, the topography of the airport and
surrounding area, the type and amount of air traffic
to be serviced at the airport, aircraft performance
requirements, and aircraft noise.

Runway Configurations
The term ―runway configuration‖ refers to the
number and relative orientations of one or more
runways on an airfield. Many runway
configurations exist. Most configurations are
combinations of several basic configurations.
The basic configurations are
• Single runways
• Parallel runways
• Intersecting runways
• Open-V runways

Runway orientation
Runway is usually oriented in the direction of
the prevailing winds. The head wind i.e. The
direction of wind opposite to the direction of
landing and take-off, provides greater lift on
the wings of the aircraft when it is taking off.

FACTORS AFFECTING RUNWAY
ORIENTATION
• WIND
• AIRSPACE AVAILABILITY
• ENVIRONMENTAL FACTORS
• OBSTRUCTIONS TO NAVIGATION
• AIR TRAFFIC CONTROL VISIBILITY
• WILD LIFE HAZARDS
• TERRAIN AND SOIL CONSIDERATION

Wind direction indicator
• It may be a wind cone, usually placed at the centre
of the segmented circle marker. This helps the pilot
in locating the airport and the wind direction
indicator. The panel forming the segmented circle
markers are gable roof shaped with a pitch of at
least 1 to 1. this enhances the visibility of the
segmented circle and the pilot will be able to detect
it from a considerable distance ahead. In most of
the cases, the panels are painted white so as to
obtain a distinctive colour contrast between the
marker and its surroundings and to protect them
against weather.

Wind rose
• The wind data i.e. Direction, duration and
intensity are graphically represented by a
diagram called wind rose.
• The data should usually be collected for a period
of at least 5 years and preferably of 10 years, so
as to obtain an average data with sufficient
accuracy.
• Wind rose diagrams can be plotted in two types
1. showing direction and duration of wind
2. Showing direction duration and intensity of
wind.

• Type – I: This type of wind rose is illustrated in fig. the radial lines
indicate the wind direction and each circle represents the duration of
wind. The values are plotted along the north direction in fig similarly
other values are also plotted along the respective directions. All plotted
points are then joined by straight lines.
• The best direction of runway is usually along the direction of the longest
lone on wind rose diagram. If deviation of wind direction up to 22.5º +
11.25ºfrom their direction of runway is thus along NS direction of landing
and take off is permissible the percentage of time in a year during which
runway can safely be used for landing and take off will be obtained by
summing the percentages of time along NNW, N, NNE, SSE, S and SSW
directions. This comes to 57.6 percent. The total percentage of the time
therefore comes to 57.0 + 13.5 = 70.5. This type of wind rose does not
account for the effect of cross wind component.

• Type – II : this type of wind rose is illustrated in fig. the wind data as in the
previous type is used for this case. Each circle represents the wind
intensity to some scale. The values entered in each segment represent the
percentage of time in a year during which the wind having a particular
intensity blows from the respective direction. The procedure for
determining the orientation of runway from this type of wind rose is
described.
• Draw three equi spaced parallel lines on a transparent paper strip in such a
way that the distance between the two near by parallel lines is equal to
the permissible cross wind component. This distance is measured with the
same scale with which the wind rose diagram is drawn the permissible
cross wind component is 25kph. Place the transparent paper strip over the
wind rose diagram in such a way that the central line passes through the
centre of the diagram. With the centre of wind rose rotate the tracing
paper and place it in such a position that the sum of all the values
indicating the duration of wind within the two outer parallel lines is the
maximum. The runway should be thus oriented along the direction
indicated by the central line. The wind coverage can be calculated by
summing up all the percentages

Basic Runway Length
• The basic runway length is determined form the
performance characteristics of aircraft using
airport. The following cases are usually
considered Normal landing case, Normal takeoff
case, Engine failure case.
• Runway length is an important factor for
adequate aircraft performance and cost of airport
layout. The short range aircraft needs lesser
runway length than the long range type, since
there is a smaller fuel requirement.

Correction for elevation, temperature
and gradient
• Airports are constructed in different elevation
different atmospheric temperature and
gradient, in contrast to the assumption made
for basic runway length. Therefore correction
required for changes in each components.

Correction in elevation
• All other things being equal, the higher the field
elevation of the airport, results the less dense the
atmosphere, requiring longer runway lengths for
the aircraft to get to the appropriate
groundspeed to achieve sufficient lift for takeoff.
For airports at elevation above sea level, the
design runway length is 300 ft plus 0.03 ft for
every foot above sea level. ICAO recommends the
basic runway length should increase at rate of 7%
per 100 m rise in elevation over MSL.

Correction in temperature
• With rise of reference temperature same effect is there as
that of elevation. The airport reference temperature
defined as monthly mean of average daily temperature (Ta)
for the hottest month of the year plus one third the
difference of this temperature and monthly mean of the
maximum daily temperature(Tw) for same month of the
year. Reference Temperature = Ta + (Tw – Ta)/3
• ICAO recommends the basic runway length after have
been corrected for elevation, should further increase at the
rate of 1% for every 10C increase of reference temperature.
If both correction increases more than 35% ICAO
recommended specific site study should be conducted.

Correction for gradient
• Steeper gradient require greater consummation
of energy and longer length of runway to attain
the desired speed. ICAO does not recommend
any correction. FAA recommend after correction
for elevation and temperature a further increase
in runway length at arte of 20% for every 1
percent effective gradient. Effective gradient is
defined taking maximum difference between
elevation between lowest point and highest point
in the runway divided by length of the runway.

Actual length of Runway
• F.A.A. specifies a gradient correction of the rate of
20% of the length corrected for altitude &
temperature for each 1% of the effective runway
gradient. This is determined by dividing the
maximum difference in the runway centreline
elevation by the total length of runway.
• As per recommendation of ICAO under the
minimum clearances, 60m additional length on
either end of the runway should be graded. The
total length of landing strip therefore comes to
(L+120m) where L is the basic runway length.
• According to ICAO recommendations total
correction percentage for altitude and temperature
should not exceed 35%.

Runway geometrics (ICAO)
Airport
Types
Basic Runway Length Runway
Pavement Width
Max.
longitudinal
grade %Maximum Minimum
m ft m ft m ft
A 2100 7000 45 150 1.5
B 2099 6999 1500 5000 45 150 1.5
C 1490 4999 900 3000 30 100 1.5
D 899 2999 750 2500 22.5 75 2.0
E 749 2499 600 2000 18 60 2.0

Taxiways
• Taxiways are defined paths on the airfield surface which are
established for the taxiing of aircraft and are intended to
provide a linkage between one part of the airfield and another.
Basically it established the connection between runway,
terminal building and hanger.
• The main function of the taxiway is to provide access to
aircrafts from the runway to the loading apron or service
hanger and back.
• Taxiways are arranges such that the aircraft which have just
landed and are taxiing towards the apron, do not interfere with
the aircrafts taxiing for take-off.
• At busy airports, these are located at various points along the
runways. As far as possible, the intersection of taxiway and
runway should be avoided.
• The taxiway route should be shortest possible distance to
minimise terminal delay.

Exit Taxiway
• The function of exit taxiways, or runway turnoffs
as they are sometimes called, is to minimize
runway occupancy by landing aircraft.
• Exit taxiways can be placed at right angles to the
runway or some other angle to the runway. When
the angle is on the order of 30°, the term high-
speed exit is often used to denote that it is
designed for higher speeds than other exit
taxiway configurations.

Location of Exit Taxiways
• The location of exit taxiways depends on the mix of aircraft, the
approach and touchdown speeds, the point of touchdown, the
exit speed, the rate of deceleration, which in turn depends on
the condition of the pavement surface, that is, dry or wet, and
the number of exits.
• While the rules for flying transport aircraft are relatively
precise, a certain amount of variability among pilots is bound to
occur especially in respect to braking force applied on the
runway and the distance from runway threshold to touchdown.
The rapidity and the manner in which air traffic control can
process arrivals is an extremely important factor in establishing
the location of exit taxiways.
• The location of exit taxiways is also influenced by the location of
the runways relative to the terminal area.

Holding Aprons
• Holding aprons, holding pads, run-up pads, or holding
bays as they are sometimes called, are placed adjacent
to the ends of runways.
• The areas are used as storage areas for aircraft prior to
takeoff. They are designed so that one aircraft can
bypass another whenever this is necessary.
• For piston-engine aircraft the holding apron is an area
where the aircraft instrument and engine operation can
be checked prior to takeoff.
• The holding apron also provides for a trailing aircraft to
bypass a leading aircraft in case the takeoff clearance of
the latter must be delayed for one reason or another, or
if it experiences some malfunction.

Hanger
• The primary function of hanger is to provide an
enclosure for servicing, over hauling and doing
repairs of the aircrafts.
• They are usually constructed of steel frames and
covered with G.I. sheets.
• They are also provided with machine shops and
stores for repair parts.
• The size of hanger depends upon the size of aircraft
and its turning radius. The number of hangers
depend upon the peak hour volume of aircrafts and
demand of hangers on rental basis by different
airline agencies.

Terminal building
• The terminal area is the major interface between the
airfield and the rest of the airport. It includes the facilities
for passenger and baggage processing, cargo handling, and
airport maintenance, operations, and administration
activities.
• The purpose of airport building or terminal building is to
provide shelter and space for various surface activities
related to the air transportation. As such they are planned
for maximum efficiency, convenience and economy.
• The extent of building area in relation to the landing area
depends upon the present and future anticipated use of
airport.

Aircraft parking
• Apron size and gate area are very much dependent
upon the manner in which aircrafts are parked, with
respect to terminal building and the manner aircrafts
manoeuvre in and out of parking position in the gate.
• Five basic aircraft parking patterns are as follows:
 Nose-in Parking
 Nose-out Parking
 Angle nose-in Parking
 Angle nose-out Parking
 Parallel Parking

AIRPORT MAKING AND LIGHTING
• Visual aids assist the pilot on approach to an airport,
as well as navigating around an airfield and are
essential elements of airport infrastructure.
• As such, these facilities require proper planning and
precise design. These facilities may be divided into
three categories: lighting, marking, and signage.

Approach lighting or surface
lighting
Specific lighting systems include:
• Approach lighting
• Runway threshold lighting
• Runway edge lighting
• Runway centerline and touchdown zone
lights
• Runway approach slope indicators
• Taxiway edge and centerline lighting

Obstruction Lighting
• Obstructions are identified by fixed,
flashing, or rotating red lights or beacons.
All structures that constitute a hazard to
aircraft in flight or during landing or takeoff
are marked by obstruction lights having a
horizontally uniform intensity duration and
a vertical distribution design to give
maximum range at the lower angles (1.5°
to 8°) from which a colliding approach
would most likely come

Approach Lighting
• Approach lighting systems (ALS) are designed
specifically to provide guidance for aircraft
approaching a particular runway under night
time or other low-visibility conditions. While
under night time conditions it may be possible
to view approach lighting systems from
several miles away, under other low-visibility
conditions, such as fog, even the most intense
ALS systems may only be visible from as little
as 2500 ft from the runway threshold.

Threshold Lighting
• During the final approach for landing, pilots must make
a decision to complete the landing or execute a missed
approach. The identification of the threshold is a major
factor in pilot decisions to land or not to land. For this
reason, the region near the threshold is given special
lighting consideration. The threshold is identified at
large airports by a complete line of green lights
extending across the entire width of the runway, and at
small airports by four green lights on each side of the
threshold. The lights on either side of the runway
threshold may be elevated. Threshold lights in the
direction of landing are green but in the opposite
direction these lights are red to indicate the end of the
runway.

Runway Lighting
• After crossing the threshold, pilots must complete a touchdown and
roll out on the runway. The runway visual aids for this phase of
landing are be designed to give pilots information on alignment,
lateral displacement, roll, and distance. The lights are arranged to
form a visual pattern that pilots can easily interpret.
• At first, night landings were made by floodlighting the general area.
Various types of lighting devices were used, including automobile
headlights, arc lights, and search lights. Boundary lights were added to
outline the field and to mark hazards such as ditches and fences.
Gradually, preferred landing directions were developed, and special
lights were used to indicate these directions. Floodlighting was then
restricted to the preferred landing directions, and runway edge lights
were added along the landing strips. As experience was developed,
the runway edge lights were adopted as visual aids on a runway. This
was followed by the use of runway center line and touchdown zone
lights for operations in very poor visibility.

Runway Edge Lights
• Runway edge lighting systems outline the edge of runways during night
time and reduced visibility conditions. Runway edge lights are classified by
intensity, high intensity (HIRL), medium intensity (MIRL), and low intensity
(LIRL). LIRLs are typically installed on visual runways and at rural airports.
MIRLs are typically installed on visual runways at larger airports and on
non-precision instrument runways, HIRLs are installed on precision-
instrument runways. Elevated runway lights are mounted on frangible
fittings and project no more than 30 in above the surface on which they
are installed. They are located along the edge of the runway not more
than 10 ft from the edge of the full-strength pavement surface. The
longitudinal spacing is not more than 200 ft. Runway edge lights are white,
except that the last 2000 ft of an instrument runway in the direction of
aircraft operations these lights are yellow to indicate a caution zone.

Runway Center line and Touchdown
Zone Lights
• As an aircraft traverses over the approach lights, pilots are
looking at relatively bright light sources on the extended
runway center line. Over the runway threshold, pilots continue
to look along the center line, but the principal source of
guidance, namely, the runway edge lights, has moved far to
each side in their peripheral vision. The result is that the
central area appears excessively black, and pilots are virtually
flying blind, except for the peripheral reference information,
and any reflection of the runway pavement from the aircraft‘s
landing lights. Attempts to eliminate this ―black hole‖ by
increasing the intensity of runway edge lights have proven
ineffective. In order to reduce the black hole effect and provide
adequate guidance during very poor visibility conditions,
runway center line and touchdown zone lights are typically
installed in the pavement.

Runway End Identifier Lights
• Runway end identifier lights (REIL) are
installed at airports where there are no
approach lights to provide pilots with positive
visual identification of the approach end of
the runway. The system consists of a pair of
synchronized white flashing lights located on
each side of the runway threshold and is
intended for use when there is adequate
visibility.

Taxiway Lighting
• Either after a landing or on the way to takeoff, pilots must maneuver the
aircraft on the ground on a system of taxiways to and from the terminal and
hangar areas. Taxiway lighting systems are provided for taxiing at night and
also during the day when visibility is very poor, particularly at commercial
service airports.
• In order to avoid confusion with runways, taxiways must be clearly identified.
• Runway exits need to be readily identified. This is particularly true for high-
speed runway exits so that pilots can be able to locate these exits 1200 to
1500 ft before the turnoff point.
• Adequate visual guidance along the taxiway must be provided.
• Specific taxiways must be readily identified.
• The intersections between taxiways, the intersections between runways and
taxiways, and runway-taxiway crossings need to be clearly marked.
• The complete taxiway route from the runway to the apron and from the
apron to the runway should be easily identified. There are two primary types
of lights used for the designation of taxiways. One type delineates the edges
of taxiways and the other type delineates the center line of the taxiway.

Taxiway Edge Lights
• Taxiway edge lights are elevated blue colored bidirectional lights
usually located at intervals of not more than 200 ft on either
side of the taxiway. The exact spacing is influenced by the
physical layout of the taxiways. Straight sections of taxiways
generally require edge light spacing in 200-ft intervals, or at
least three lights equally spaced for taxiway straight line
sections less than 200 ft in length.
• Closer spacing is required on curves. Light fixtures are located
not more than 10 ft from the edge of full strength pavement
surfaces. Taxiway centerline lights are in-pavement bidirectional
lights placed in equal intervals over taxiway centerline
markings.
• Taxiway centreline lights are green, except in areas where the
taxiway intersects with a runway, where the green and yellow
lights are placed alternatively.

Runway and Taxiway Marking
• In order to aid pilots in guiding the aircraft on
runways and taxiways, pavements are marked
with lines and numbers. These markings are of
benefit primarily during the day and dusk. At
night, lights are used to guide pilots in landing
and maneuvering at the airport.
• White is used for all markings on runways
and yellow is used on taxiways and aprons.

Runway Threshold Markings
• Runway threshold markings identify to the pilot the
beginning of the runway that is safe and available for
landing.
• Runway threshold markings begin 20 ft from the runway
threshold itself. Runway threshold markings consist of
two series of white stripes, each stripe 150 ft in length
and 5.75 ft in width, separated about the centerline of
the runway. On each side of the runway centerline, a
number of threshold marking stripes are placed.
• For example, for a 100-ft runway, eight stripes are
required, in two groups of four are placed about the
centerline. Stripes within each set are separated by 5.75
ft. Each set of stripes is separated by 11.5 ft about the
runway centerline.

Runway Centerline Markings
• Runway centerline markings are white, located on
the centerline of the runway, and consist of a line of
uniformly spaced stripes and gaps.
• The stripes are 120 ft long and the gaps are 80 ft
long. Adjustments to the lengths of stripes and gaps,
where necessary to accommodate runway length,
are made near the runway midpoint.
• The minimum width of stripes is 12 in for visual
runways, 18 in for non precision instrument runways,
and 36 in for precision instrument runways.
• The purpose of the runway centerline markings is to
indicate to the pilot the centre of the runway and to
provide alignment guidance on landing and takeoff.

Touchdown Zone Markings
• Runway touchdown zone markings are white and consist of groups of
one, two, and three rectangular bars symmetrically arranged in pairs
about the runway centerline.
• These markings begin 500 ft from the runway threshold. The bars are
75 ft long, 6 ft wide, with 5 ft spaces between the bars, and are
longitudinally spaced at distances of 500 ft along the runway.
• The inner stripes are placed 36 ft on either side of the runway
centerline. For runways less than 150 ft in width, the width and
spacing of stripes may be proportionally reduced.
• Where touchdown zone markings are installed on both runway ends
on shorter runways, those pairs of markings which would extend to
within 900 ft of the runway midpoint are eliminated.

Taxiway Centerline and Edge
Markings
• The centerline of the taxiway is marked with a single
continuous 6-in yellow line.
• On taxiway curves, the taxiway centerline marking
continues from the straight portion of the taxiway at a
constant distance from the outside edge of the curve.
• At taxiway intersections which are designed for aircraft to
travel straight through the intersection, the centerline
markings continue straight through the intersection.
• At the intersection of a taxiway with a runway end, the
centerline stripe of the taxiway terminates at the edge of
the runway

Railway and Airport Engineering

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