TERM REPORT

DEPARTEMENT OF TRANSPORTATION ENGINEERING

UET, LAHORE

REG NO : 2020-MS-TE-111
SUBMITTED BY : IKRAM ULLAH
SUBMITTED TO : DR. Ammad Hassan Khan
DATE : 02-03-2021
 ML 1 Project
History of railway in Pakistan:
Rail transport in Pakistan began in 1855 during the British Raj. After creation of Pakistan,
1947 route miles (3,133 km) of the North Western Railways remained in India, leaving 5048
route miles (8,124 km) in Pakistan. Currently Pakistan Railways owns 11,881 kilometres
(7,383 mi) of track. All are 1,676 mm (5 ft 6 in) (broad gauge), except for some industrial
lines. The broad-gauge track axle load limit is 22.86 tonnes. The maximum speed on most
lines is 120 kilometres per hour (75 mph). Work is in progress to upgrade all main lines to
160 kilometres per hour (99 mph).
Proposed New lines:
New rail lines have been proposed by Pakistan Railways to connect Gwadar Port to Central
Asia, including:
 Karachi–Gwadar Railway Line (Makran Railway)
 Gwadar–Mastung Branch Line
 Basima–Jacobabad Branch Line
 Bostan–Zhob–Dera Ismail Khan Branch Line
 Islamabad–Muzaffarabad Branch Line
 Jhang Sadar–Risalewala Branch Line
 New rail track 1,872 kilometer in length will be laid out under the Main Line-1 (ML-1)
project, The Project will result in doubling of entire track from Karachi to Peshawar.

Railroad Network Capacity Enhancements:

Increasing railroad network capacity can be achieved without the construction of new rail
lines. In fact there are cheaper options that can help to gain efficiencies that maximize the
existing track configuration and train control technologies. However at a certain point these
improvements will no longer be able to cope with demand and therefore new construction
may be warranted. This section discusses some of the enhancements that railroads may
implement before considering new rail line construction.
1. Communications & Signaling [C&S] – For simplification, the C&S systems include
Warrant Control, Automatic Block Signaling (ABS), and Centralized Traffic Control
(CTC) (Cambridge Systematics, Inc, 2007). Each system offers increased capacity,
albeit with increasing costs. Installation of new C&S systems would be one of the
first options for capacity improvements, as it will decrease the degradation of the
weakest infrastructure elements, at a lower cost than other technologies such as
train or car specific technologies. Upgrading CTC from Warrant Control for one track
would cost $700,000 per mile, while upgrading the system from ABS to CTC for one
track would cost $500,000 per mile (Cambridge Systematics, Inc, 2007).
2. Rail car capacity – This involves the introduction of a rail car that is capable of
hauling greater loads as rated per axle. This increased capacity per car, would allow
more product for the same number of cars, but would result in operational changes
or improvements, such as additional locomotives to haul the train and rail hardware
upgrades to handle the increased weight. As a result, the cost for the increased
capacity rail cars, together with the cost of new rail hardware (tracks and ties) may
result in a considerable investment. In 2009, the average cost for a new freight car
on a Class I railroad was $98,090. If capacity were to increase, this would result in a
higher cost of the new car, as well as the potentially higher cost of increase
maintenance and replacement components (Association of American Railroads,
 2010). Electrification – This is the replacement of diesel-electric locomotives with
locomotives operating via an electrically-fed infrastructure parallel to the railway.
Some of the benefits of electrification include;
o Increased performance of acceleration and deceleration
o Closer headways
o Greater horsepower per locomotive
o Regenerative braking that results in energy normally lost as heat transferred
back into the electrical system
o Fewer moving parts resulting in fewer and less costly routine maintenance
inspections.
3. Facilities – These are the yards, sidings, maintenance, and facilities that allow trains
to navigate freight from origin to destination with minimal dwell time, and efficient
equipment utilization, thereby allowing reliable service. Investments in facilities can
include expanded and enlarged facilities, or even the construction of new facilities.
Both could be done strategically to allow the greatest utilization of the investment.
Examples of such facilities include the Union Pacific’s Bailey yard in Nebraska and
Global III Intermodal Terminal in Illinois, where optimization of operations within and
between railroads is done both tactically and strategically(Union Pacific).
4. Electronically controlled pneumatic brakes [ECPB] – This is a braking system on each
train car that is electronically controlled by the locomotive and results in faster brake
applications (Mandelbaum, 2009). The current method is controlled by the
locomotive and rather than waiting for the change in air pressure from one end of
the train to the other to start the application of brakes, ECPB simultaneously applies
brakes. The capacity (number of trains on a railway) would increase as trains
wouldrespond faster and have the ability to operate with smaller headways.
Estimates for the Powder River Basin operations of the Union Pacific and BNSF
suggest that these costs would be $432 million for 2,800 locomotives and 80,000
freight cars, with an annual benefit of $157million (Federal Railroad Administration,
2007).
5. Positive Train Control [PTC] – This locomotive computer monitoring allows
verification of current place, performance and adherence to train orders. This
monitoring results in a failsafe that may prevent accidents and offer greater control
of each train on the network, possibly resulting in smaller headway and increased
use of track (Federal Railroad Administration). The cost for PTC is estimated at $13.2
billion and is being federally mandated on all locomotives by 2015 (Association of
American Railroads).
6. Track realignment – This involves the redesigning of the route that a railway follows.
Whether it is rerouting for geographical or land use reasons, removing restrictive
curves, or decreasing grades, the potential benefit would be more consistent speeds
with less power requirements to haul the same train. The cost for track realignment
projects depends on numerous factors and therefore is difficult to estimate. Any
realignment would bring a benefit to only those trains that traversed the railway in
question.
 Why ML1 is on top Priority

China-Pakistan Economic Corridor (CPEC):

In line with the government’s Vision 2025 for infrastructure development, Pakistan Railways
is to undertake necessary steps to increase its share in the overall transport sector of
Pakistan during the next 10 years. A priority project in this regard is China-Pakistan
Economic Corridor (CPEC) and upgradation of ML-1 route that connects Karachi, Lahore, and
Peshawar (main cities of Pakistan). China and Pakistan have signed memorandum of
understanding (MoU) to increase the speed of the railway connecting Karachi and Peshawar
as well as to upgrade its signal system and railway stations. This also includes efforts of
doubling the train tracks to control traffic. Doubling of track from Khanewal to Raiwind is
near to complete. Provision of signaling system on Lodhran-Khanpur-Kotri section and
centralized traffic control are also underway.
Freight Demand: Past, Current, and Future Trends
Rail freight demand is an important component of rail operations. The demand for rail
freight transport services are derived in nature just like the demand for many other inputs
such as labor, energy etc. by the firms. Freight transport is usually considered as an input to
the production process of firms and it is derived from the demand for goods spatially
differentiated from the locations of production. The main objective of rail freight transport
demand analysis is to identify the main factors that affect rail freight demand, which can
further be used for rail transport planning and demand management. The performance of
rail freight transport in Pakistan during the last two decades from 1997–98 to 2016–17 is
provided in Table 1. Rail freight transport is measured in both total tons (millions) and ton-
kilometers (millions). PR has carried a total of 5.97 million tons and 4447.3 million ton-
kilometers of freight in 1997–98, which, although not consistently, has increased to 7.23
million tons and 6187.3 million ton-kilometers after a decade. The improvement in most of
this period was due to the development projects implemented by PR to improve its services.
The freight analysis provided above are an alarm to Pakistan railway to increase its track
capability to cope the freight demands that may be increase in coming years.
Passenger Demand: Future Trends:

Railway transport demand may be divided into passenger and freight

demand. Passenger demand
consists of intercity demand and commuting demand. Intercity demand is
based on business activities or
leisure. The same holds for commuting, but all components of commuting
demand has similar character-
istics and for this reason there is no difference between business and
leisure. Freight demand is almost
always part of the industrial process. It is under the great influence of type
of goods, geographical and
socio-economic parameters, pricing policy, seasonality, etc
Railway transport demand may be divided into passenger and freight
demand. Passenger demand
consists of intercity demand and commuting demand. Intercity demand is
based on business activities or
leisure. The same holds for commuting, but all components of commuting
demand has similar character-
istics and for this reason there is no difference between business and
leisure. Freight demand is almost
always part of the industrial process. It is under the great influence of type
of goods, geographical and
socio-economic parameters, pricing policy, seasonality, etc
Railway transport demand may be divided into passenger and freight
demand. Passenger demand
consists of intercity demand and commuting demand. Intercity demand is
based on business activities or
leisure. The same holds for commuting, but all components of commuting
demand has similar character-
istics and for this reason there is no difference between business and
leisure. Freight demand is almost
always part of the industrial process. It is under the great influence of type
of goods, geographical and
socio-economic parameters, pricing policy, seasonality, etc
Considering railway demand forecasting, one classification of forecasting methods concerns
the time in the future they cover. Long-term forecasts look ahead 5 to 10 years. Medium-
term forecasts extend from 2 to 5 years into the future and short-term forecasts involve
predictive intervals within 6 to 18 months. Short and medium-term forecasts are required
for activities that range from operations management to budgeting and selecting new
research and development projects in railway transport. Long term forecasts impact issues
such as strategic planning in the domain of railway infrastructure and mobile capacities.The
time horizon affects the choice of forecasting method because of the availability and
relevance of historical data, time available to make the forecast, cost involved, seriousness
of errors, effort considered worthwhile (Waters, 2008). Despite the wide range of problem
situations that arise in the field of railway transportation (railway operations management,
marketing, finance and risk management) there are only two types of forecasting
techniques – qualitative and quantitative methods.
Qualitative forecasting techniques are often subjective in nature and require judgment on
the part of experts. These techniques are often used in situations where there is little or no
historical data (Figure 1).
Quantitative forecasting methods for the future railway demand are used in case a
company has records of past sales and knows the factors that affect them. Quantitative
methods may be classified into two broad categories (Figure 2).
Pakistan Railway passengers, 1995 - 2018: For that indicator, we provide data for Pakistan
from 1995 to 2018. The average value for Pakistan during that period was 21392 million
passengers times km's with a minimum of 17555 million passengers times km's in 1995 and
a maximum of 26446 million passengers times km in 2007 (chart 1).
 chart 1

Introduction High Speed Rail Systems

Within the general concept of HSR, there are multiple maximum speeds that require
differentiation. Each speed is able to offer certain benefits for associated costs, allowing a
mix of service options to best fit the need of the area in question. Classifications of service
by speed have been done by agencies such as the FRA, which defined them as Emerging (up
to 90mph), Regional (90 –125mph) and Core Express (125 - 250mph). This classification may
be appropriate for distinguishing the service as expected by the ridership, but in terms of
railway construction, a new set of classifications is necessary. The classification used in this
research includes; Conventional (79 - 90mph), Incremental (110mph), Higher-Speed
(125mph), High-Speed (150mph), and Very High Speed (220mph). This reclassification allows
the planner to analyze an individual service, rather than grouping of services as denoted by
the FRA definitions (Federal Railroad Administration, 2011).
1. Conventional - represent passenger operations at 79mph to 90mph on existing
infrastructure alongside freight services. In most instances, these conventional
services are operated upon the private freight railroad right-of-way (ROW) as a
tenant. Therefore, improvements in capacity will be provided by the freight
railroads. Nearly all commuter and Amtrak services are considered conventional
(Peterman, et al., 2009), (SunRail, 2011), (Morlock, et al, 2004).
2. Incremental - represent projects that operate at 110mph maximum speed on
existing track along with existing freight services or alone. The maximum speeds
attained are low enough that safe operation with the appropriate communications
and signaling (C&S) system allows mixing of services. Above this speed level, the
speed differential is too great to justify the mixing of services and a dedicated and
separate infrastructure is needed (White, 2000).
3. Higher-Speed and High-Speed - represent projects that operate at 125mph and
150mph. The speed differential with freight services is too great at this speed,
requiring a separate infrastructure to operate above conventional passenger service
speeds. Amtrak’s North East Corridor is the only example of High-Speed service in
the United States, with only portions of the Washington DC to Boston line allowing
the maximum designed speed of 150mph to be reached (Amtrak, 2010). The
California High Speed Rail Authority has a master plan that includes a 220 - mph
service connecting Los Angeles to San Francisco and Sacramento and San Diego
(California High-Speed Rail Authority, 2009).

Stages of construction of the railway

In order to establish constructive relations with the contractor and ensure maximum
effective interaction during the construction of the access rail track, the customer must be
well aware of the types of work required, their sequence, resource intensity and
approximate duration. Below is an approximate sequence of steps necessary for the
construction of an access Railway track after the election and registration of rights to the
land

1. Preliminary engineering and geodetic survey: Obtaining technical specifications (TU)

from road management enterprises: stations for connecting the railway (DS), track
distances (IF), signaling and communication distances (SCH), power supply distances
(EF), etc. Coordination of technical specifications in the departments (traffic, roads,
communications and signaling, power supply), from the chief engineer of the road
departments, in the road (traffic, way, connection and signaling, power supply)
 management services and their approval by the chief engineer (NG) in the road
management.
2. Final engineering-geodetic and engineering-geological surveys: Obtaining technical
conditions from owners of engineering networks crossing the access road or passing
in close proximity to it: gas pipelines, power lines, communication lines, water supply
networks, cable networks, highways, etc.
3. Design Approval Process: After the aforementioned documents have been approved
by the District, the District Railroad Coordinator forwards them on to the Contract
Specialist who then coordinates the review of the documents with the proper
Division personnel. Division reviews may include:
 Bridge Design
 Grade Crossing Warning Devices
 Traffic Signal Preemption
 Track Design
 Hydraulics
 Roadway Design
 Pedestrian Elements
 Landscape Architecture.
After all comments have been resolved from the divisions, the Contract Specialist
forwards the documents to the railroad company for review.
4. Construction works:
 Excavation: excavation of the embankment or excavation device, movement of the
soil along the front of the work, leveling, compacting (tamping) and, if necessary,
dehumidification of the future roadbed (drainage of groundwater, etc).
 Installation of artificial structures: laying culverts, drainage trays, etc. (Carried out
before or after excavation).
 Laying of the upper structure of the path: the formation of a ballast prism, the laying
of the under-rail base (sleepers), the laying and joining of rails, the laying of turnouts
and deaf intersections.
 Ballasting and alignment of the path.
 Arrangement of railway crossings.
 Construction of buildings, structures, platforms, elevated paths:
 Formation of a commission composed of: representative of the customer,
representative of the contractor, representative of the contiguity infrastructure, (the
commission is collected by the customer, the director of the customer enterprise
presides, the commission is appointed for 1-2 weeks).

Concept of Industry Life Cycle:

An industry life cycle analysis allows for firms within the industry to frame policies and
nature of an industry changes as the industry moves through its life cycle. The main views of
how firms and industries progress are as follows: as some businesses mature and the source
of competition shifts from product innovation to process innovation. The idea of industry
life cycle was presented by Michael in 1980 and, according to this concept, the industry is
the most important part of a firm. The criteria for differentiating changes of individual
stages are an increase or decrease in product and innovation process.

Different Phases of Industry Life Cycle

The basic idea of life cycle theory comes from biology parallel with the life cycle of an
organism. According to industry life cycle, all industries go through four different phases,
where each particular phase requires a policy that will effectively absorb the specific
situations of the phase. Industrial life cycle curve can usually be a sales revenue on the
vertical axis and time on the horizontal axis. It is generally divided into four stages,
introduction, growth, maturity, and decline, and the industry life cycle analysis allows the
management to adjust the business according to the needs of industry.

 Introduction Stage: Evolving industries are new and product appears on the market
in the introduction stage. There is small market demand and customers are not
aware of its potential benefits, so advertising is usually necessary and investments
are needed to build upmarket.
 Growth Stage: In growth stage, the product has been successful and there is rapid
spread of awareness and use of the product. With the development of new
technologies, the unit cost is reduced, quality is improved, and demand is increasing,
in addition to growth in profits.
 Maturity Stage: In the maturity stage, the market share reaches a certain level but,
at the same time, market demand is relatively slow and stable and industry is in
recession. This transition from a phase of growth to maturity is an almost critical
period for firms in the industry. This is the period during which fundamental changes
are taking place in the company and are induced and also followed by a number of
trends.
 Decline Stage: Decline phase is characterized by falling profit margins, reduction in
production, lower investment, and fewer competitors. In this phase of the industry
life cycle, the strategic choice is the harvesting strategy as a strategic management
decision to reduce investment in the business with the hope of reducing costs or
improving cash flow. Customers have been attracted to other products, due to the
fact that products and services cannot meet the market demand or lower prices of
alternative products, making profit margins decline and outputs start to decrease
and industry will enter the decline stage of the industry life cycle.

However, if the industry after recession comes through certain industrial innovations and
upgradations, the output of the industry will stop to decline and may revive the industry and
may bring a new round of industry life cycle.

DESIGN CONSIDERATIONS

1. Alignment Design

In a perfect world, all railway alignments would be tangent and flat, thus providing for the
most economical operations and the least amount of maintenance. Though this is never the
set of circumstances from which the designer will work, it is that ideal that he/she must be
cognizant to optimize any design.
From the macro perspective, there has been for over 150 years, the classic railway location
problem where a route between two points must be constructed. One option is to
construct a shorter route with steep grades. The second option is to build a longer route
with greater curvature along gentle sloping topography. The challenge is for the designer to
choose the better route based upon overall construction, operational and maintenance
criteria.

Suffice it to say that in today s environment, the designer must also add to the decision
model environmental concerns, politics, land use issues, economics, long-term traffic levels
and other economic criteria far beyond what has traditionally been considered. These
added considerations are well beyond what is normally the designer s task of alignment
design, but they all affect it. The designer will have to work with these issues occasionally,
dependent upon the size and scope of the project.

On a more discrete level, the designer must take the basic components of alignments,
tangents, grades, horizontal and vertical curves, spirals and superelevation and construct an
alignment, which is cost effective to construct, easy to maintain, efficient and safe to
operate. There have been a number of guidelines, which have been developed over the
past 175 years, which take the foregoing into account. The application of these guidelines
will suffice for approximately 75% of most design situations. For the remaining situations,
the designer must take into account how the track is going to be used (train type, speed,
frequency, length, etc.) and drawing upon experience and judgment, must make an
educated decision. The decision must be in concurrence with that of the eventual owner or
operator of the track as to how to produce the alignment with the release of at least one of
the restraining guidelines.

Though AREMA has some general guidance for alignment design, each railway usually has its
own design guidelines, which complement and expand the AREMA recommendations.
Sometimes, a less restrictive guideline from another entity can be employed to solve the
design problem. Other times, a specific project constraint can be changed to allow for the
exception. Other times, it is more complicated, and the designer must understand how a
train is going to perform to be able to make an educated decision. The following are brief
discussions of some of the concepts which must be considered when evaluating how the
most common guidelines were established.

Trains, and in this example the chain, will always have longitudinal forces acting along their
length as the train speeds up or down, as well as reacting to changes in grade and curvature.
It is not unusual for a train to be in compression over part of its length (negative longitudinal
force) and in tension (positive) on another portion. These forces are often termed buff
(negative) and draft (positive) forces. Trains are most often connected together with
couplers (Figure 6-10). The mechanical connections of most couplers in North America have
several inches (up to six or eight in some cases) of play between pulling and pushing. This is
termed slack.

A freight train is most commonly comprised of power and cars. The power may be one or
several locomotives located at the front of a train. The cars are then located in a line behind
the power. Occasionally, additional power is placed at the rear, or even in the center of the
train and may be operated remotely from the head-end.
As the chain is pulled in a straight line, the remainder of the chain follows an identical path.
However, as the chain is pulled around a corner, the middle portion of the chain wants to
deviate from the initial path of the front-end. On a train, there are three things preventing
this from occurring. First, the centrifugal force, as the rail car moves about the curve, tends
to push the car away from the inside of the curve. When this fails, the wheel treads are
both canted inward to encourage the vehicle to maintain the course of the track. The last
resort is the action of the wheel flange striking the rail and guiding the wheel back on
course. Attempting to push the chain causes a different situation. A gentle nudge on a short
chain will generally allow for some movement along a line. However, as more force is
applied and the chain becomes longer, the chain wants to buckle in much the same way an
overloaded, un-braced column would buckle (See Figure 6-12). The same theories that
Euler applied to column buckling theory can be conceptually applied to a train under heavy
buff forces. Again, the only resistance to the buckling force becomes the wheel/rail
interface.

If one considers that a long train of 100 cars may be 6000’ long, and that each car might
account for six inches of slack, it becomes mathematically possible for a locomotive and the
front end of a train to move fifty feet before the rear end moves at all. As a result, the
dynamic portion of the buff and draft forces can become quite large if the operation of the
train, or more importantly to the designer, the geometry of the alignment contribute
significantly to the longitudinal forces.

2. Sleeper Design

A railway sleeper is a rectangular object used as a base for railroad tracks. Ties are members
generally laid transverse to the rails, on which the rails are supported and fixed, to transfer
the loads from rails to the ballast and subgrade, and to hold the rails to the correct gauge.

key parameter having a large influence on buckling strength is the sleeper-ballast lateral
resistance. This resistance has three contributing components, and indicated by Kish (2011):
bottom friction (Fb), side friction (Fs), and end or shoulder restraint (Fe).

New shapes for the sleepers were proposed to be studied. The designs were based on the
addition of prominent wings around the sleeper in order to increase some of the
contributing components of the lateral resistance.

3. Joints and Crossing Design

The track on a railway or railroad, also known as the permanent way, is the structure
consisting of the rails, fasteners, railroad ties (sleepers, British English) and ballast (or slab
track), plus the underlying subgrade. It enables trains to move by providing a dependable
surface for their wheels to roll upon. For clarity it is often referred to as railway track (British
English and UIC terminology) or railroad track (predominantly in the United States). Tracks
where electric trains or electric trams run are equipped with an electrification system such
as an overhead electrical power line or an additional electrified rail.

There are different types of modern track used in Railway engineering.

 1. Jointed track:

Jointed track is made using lengths of rail, usually around 20 m (66 ft) long (in the UK) and
39 or 78 ft (12 or 24 m) long (in North America), bolted together using perforated steel
plates known as fishplates (UK) or joint bars (North America).

Fishplates are usually 600 mm (2 ft) long, used in pairs either side of the rail ends or bolted
together (usually four, but sometimes six bolts per joint). The bolts have alternating
orientations so that in the event of a derailment and a wheel flange striking the joint, only
some of the bolts will be sheared, reducing the likelihood of the rails misaligning with each
other and exacerbating the derailment. This technique is not applied universally; European
practice being to have all the bolt heads on the same side of the rail.

Small gaps which function as expansion joints are deliberately left between the rail ends to
allow for expansion of the rails in hot weather. European practice was to have the rail joints
on both rails adjacent to each other, while North American practice is to stagger them.
Because of these small gaps, when trains pass over jointed tracks they make a "clickety-
clack" sound. Unless it is well-maintained, jointed track does not have the ride quality of
welded rail and is less desirable for high speed trains. However, jointed track is still used in
many countries on lower speed lines and sidings, and is used extensively in poorer countries
due to the lower construction cost and the simpler equipment required for its installation
and maintenance.

A major problem of jointed track is cracking around the bolt holes, which can lead to
breaking of the rail head (the running surface). This was the cause of the Hither Green rail
crash which caused British Railways to begin converting much of its track to continuous
welded rail.

2. Insulated Joints:

Where track circuits exist for signalling purposes, insulated block joints are required. These
compound the weaknesses of ordinary joints. Specially-made glued joints, where all the
gaps are filled with epoxy resin, increase the strength again. As an alternative to the
insulated joint, audio frequency track circuits can be employed using a tuned loop formed in
approximately 20 m (66 ft) of the rail as part of the blocking circuit. Some insulated joints
are unavoidable within turnouts.

Another alternative is the axle counter, which can reduce the number of track circuits and
thus the number of insulated rail joints required.

3. Continuous Welded Rail (CWR):

Most modern railways use continuous welded rail (CWR), sometimes referred to as ribbon
rails. In this form of track, the rails are welded together by utilising flash butt welding to
form one continuous rail that may be several kilometres long. Because there are few joints,
this form of track is very strong, gives a smooth ride, and needs less maintenance; trains can
travel on it at higher speeds and with less friction. Welded rails are more expensive to lay
than jointed tracks, but have much lower maintenance costs. The first welded track was
used in Germany in 1924. and has become common on main lines since the 1950s.
The preferred process of flash butt welding involves an automated track-laying machine
running a strong electric current through the touching ends of two unjoined rails. The ends
become white hot due to electrical resistance and are then pressed together forming a
strong weld. Thermite welding is used to repair or splice together existing CWR segments.
This is a manual process requiring a reaction crucible and form to contain the molten iron.

CWR is laid (including fastening) at a temperature roughly midway between the extremes
experienced at that location. (This is known as the "rail neutral temperature".) This
installation procedure is intended to prevent tracks from buckling in summer heat or pulling
apart in the winter cold. In North America, because broken rails (known as a pull-apart) are
typically detected by interruption of the current in the signaling system, they are seen as
less of a potential hazard than undetected heat kinks.Joints are used in the continuous
welded rail when necessary, usually for signal circuit gaps. Instead of a joint that passes
straight across the rail, the two rail ends are sometimes cut at an angle to give a smoother
transition.

4. Bed Foundation Design:

Railway tracks are generally laid on a bed of stone track ballast or track bed, which in turn is
supported by prepared earthworks known as the track formation. The formation comprises
the subgrade and a layer of sand or stone dust (often sandwiched in impervious plastic),
known as the blanket, which restricts the upward migration of wet clay or silt. There may
also be layers of waterproof fabric to prevent water penetrating to the subgrade. The track
and ballast form the permanent way. The foundation may refer to the ballast and formation,
i.e. all man-made structures below the tracks.

Some railroads are using asphalt pavement below the ballast in order to keep dirt and
moisture from moving into the ballast and spoiling it. The fresh asphalt also serves to
stabilize the ballast so it does not move around so easily. Additional measures are required
where the track is laid over permafrost, such as on the Qingzang Railway in Tibet. For
example, transverse pipes through the subgrade allow cold air to penetrate the formation
and prevent that subgrade from melting.

MAINTENANCE

If ballast is badly fouled, the clogging will reduce its ability to drain properly. That, in turn,
causes debris to be sucked up from the sub-ballast, causing more fouling. Therefore,
keeping the ballast clean is essential. Bioremediation can be used to clean ballast.

It is not always necessary to replace the ballast if it is fouled, nor must all the ballast be
removed if it is to be cleaned. Removing and cleaning the ballast from the shoulder is often
sufficient, if shoulder ballast is removed to the correct depth. While that job was done
historically by manual labour, that process is now, as with many other railway maintenance
tasks, a mechanised one, with a chain of specially-designed railroad cars handling the task.
One wagon cuts the ballast and passes it via a conveyor belt to a cleaning machine, which
washes the ballast and deposits the dirt and ballast into other wagons for disposal or re-use.
Such machines can clean up to two kilometres (1.2 mi) of ballast in an hour.

Cleaning, however, can only be done a certain number of times before the ballast is
damaged to the point that it cannot be re-used. Furthermore, track ballast that is
completely fouled can not be corrected by shoulder cleaning. In such cases, it is necessary to
replace the ballast altogether. One method of "replacing" ballast, if necessity demands, is to
simply dump fresh ballast on the track, jack the whole track on top of it, and then tamp it
down. Alternatively, the ballast underneath the track can be removed with an under cutter,
which does not require removing or lifting the track.

The dump and jack method cannot be used through tunnels, under overbridges, or where
there are platforms. Where the track is laid over a swamp, such as the Hexham swamp in
Australia, the ballast is likely to sink continuously, and needs to be topped up to maintain its
line and level. After 150 years of topping up at Hexham, there appears to be 10 m (33 ft) of
sunken ballast under the tracks. Chat Moss in the United Kingdom is similar.

Regular inspection of the ballast shoulder is important. As noted earlier, the lateral stability
of the track depends upon the shoulder. The shoulder acquires some amount of stability
over time, being compacted by traffic, but maintenance tasks such as replacing ties,
tamping, and ballast cleaning can upset that stability. After performing those tasks, it is
necessary either for trains to run at reduced speed on the repaired sections, or to employ
machinery to compact the shoulder again.

If the track bed becomes uneven, it is necessary to pack ballast underneath sunken ties to
level the track again, which is usually done by a ballast tamping machine. A more recent,
and probably better, technique is to lift the rails and ties, and to force stones, smaller than
the track ballast particles and all of the same size, into the gap. That has the advantage of
not disturbing the well-compacted ballast on the track bed, which tamping is likely to do.
The technique is called pneumatic ballast injection (PBI), or, less formally, "stone blowing".
However, it is not as effective with fresh ballast, because the smaller stones tend to move
down between the larger pieces of ballast.