These are notes on important but little-know information about
railway engineering that is not found in most textbooks about railway
engineering. E.g.: Derailment containment.
Track supports the weight of the train and guides it. All types of
track are support structures for steel rails.
Gauge is the spacing between the inside face of
rails.
More specifically, gauge is defined and measured at 14 mm below the top
of the rail. This is usually below the curved top edge of the rail and
avoids gauge changing with slight wear.
By convention, standard gauge is
1435 mm. It is designated as the standard by the UIC. In this
case, the gauge came first and the standardization later. See https://www.grijalvo.com/Tf_Ancho_de_via/Myth_Standard_Gauge__Mark_I.htm.
The exact gauge is a result of historical accident,
rather than rationally chosen.
Standard gauge is indirectly the result of George Stephenson choosing
the gauge of mine carts when he built one of the first railways. He did
not posit this is optimal nor envisioned it would become a world-wide
standard. It is simply the gauge he was familiar with.
The existence of many gauges around the world is very unfortunate, as
trains can not normally pass between different gauges. In absence of a
centralized concerted effort to change gauge, existing gauges are
perpetuated because new equipment is built to the same gauge to be
compatible with existing equipment. See:
Curves built to a wider gauge.
When straight track is built, gauge is as close to nominal as
practicable. Some railways build curves to a slightly wider gauge with
the reasoning this will allow for better running.
From Influence
of gauge width on rail side wear on track curves:
According to the maintenance rules of Lithuanian railways, the width
of the gauge between rail head internal edges in the straight sections
and in the curves with radius ≥ 350 m, must be 1520 mm. In the curves
with smaller radius, the gauge width must be as follows: if radius is
from 349 m till 300 m – 1530 mm; if radius is ≤ 299 m – 1535 mm. The
gauge width in straight sections and curves must not broaden by more
than 6 mm and narrow down by more than 4 mm. In the sections with the
speed limitation of 50 km/h and higher, deviations must not exceed 10 mm
and 4 mm respectively. These norms are the same as in Russia and they do
not change since 1970.
See also Rules
of technical operation of railways of the Russian
Federation.
Gauge redefinition.
In the Russian Empire the gauge was 1524 mm. In the Soviet Union it was
redefined to 1520 mm. The difference is small enough that equipment is
interoperable and did not require immediate adjustment after the
redefinition.
Narrow gauges are obsolete.
Narrow gauge railways are like normal railways,
except they suck. They have less carrying capacity and less
stability for no real benefit. All existing narrow gauge railways should
be converted to Stephenson gauge.
It has been claimed that narrow gauge track is more suited for tight
curves. However, Stephenson gauge railways routinely pass through curves
with r = 100 m. If an application genuinely requires tighter
curves than what is possible with standard equipment, then the solution
is steerable bogies or independently rotating wheels, not using narrow
gauge. Tramways (incl. so-called light rail) routinely operate with
r ≤ 50 m using independently rotating wheels on Stephenson
gauge.
It has been claimed that narrow gauge saves cost. However, cost of
the track depends mostly on axle load and loading gauge. If saving such
construction costs is desired, build the track with standard gauge and
use a smaller axle load and loading gauge for that line.
Stephenson gauge is capable of very tight
curves.
For a graphical demonstration, see this video of a
ride along Mexican line L especially between Ébano, Tamaulipas and
Cárdenas, San Luis Potosí. This is using standard equipment, not even
steering bogies.
Grade.
The grade of a railway is defined as rise/run or equivalently,
F = tan α where α is the inclination
along the line of travel (0° is level track).
The longitudinal force due to the weight of the train is sin
α × weight. Note this is different from the grade (sine
instead of tangent), although in practical applications the difference
is negligible.
In most railways, grade is kept below 30 ‰.
Effect of grade on adhesion.
For a train on a grade the normal force on the track due to its weight
is F = cos α. Since α is small, cos
α is almost 1. Thus in railway engineering one neglects the
small reduction of adhesion due to grades. For example, for a grade of
5 ‰ we have cos α ≈ 0.9987
Stephenson gauge is wide enough in
practice.
Stephenson gauge gives the impression to both laypeople and railway
engineers that it is too narrow. Is that the case?
The “ideal” gauge is often thought by railway engineers to be
slightly wider than Stephenson gauge. Nonwithstanding with that,
Stephenson gauge is not so narrow that it creates problems. From The
Gauge Question: Evils of a Diversity of Gauge and a Solution,
p. 33-34.
There is a notion prevalent with the public, that a [wagon] with a
wide gauge must be much safer than one with a
narrower gauge, because less liable to
[overtopple]. This fear, I need not say, is quite unfounded on a
railway; it never happens, except in the possible case getting
altogether off the rails when going at high velocity, in which event a
[wagon] may be dashed to pieces or hurled over an embankment or
bridge and a [broader gauge] will certainly not save it. [Isambard
Kingdom Brunel] says: “I certainly never thought of the danger of
[overtoppling] from the narrowness of the [Stephenson gauge]”
Instead, the limiting factor in the capacity of wagons is the loading
gauge and axle load rating. The shuttle train running in the tunnel
between Britain and France has one of the widest loading gauges, at >
4 m and runs on Stephenson gauge.
Elements.
From top to bottom, the elements of classical railway track are:
- Rails
- Fastening system
- Sleepers
- Ballast
- Subballast
- Trackbed
Subballast and trackbed are not always present.
Ballasted track is semi-permanent.
It requires maintenance in the span of years. This usually includes
tamping and ballast cleaning. In modern times, this proccess uses
dedicated machines and is almost entirely mechanized. Usually manual
work is only required to remove and restore electrical rail bonding, if
used.
Ballasted track is operationally flexible.
The track can be disassembled with relative ease, making available the
rail, fastening system, sleepers and ballast for a different track. The
geometry can be changed by tamping, the same as used for regular
maintenance. Switches are easily installed or uninstalled.
Ballast is liable to become contaminated by dirt or
sand.
Contaminated ballast can be cleaned and returned to the same track or
used in a different one. Fully-mechanized equipment is
available.
Grade crossings.
In at-grade crossings and street-running tracks full maintenance to
ballasted track requires breaking the road on top and rebuilding it
afterwards. This could be avoided by using liftable steel or concrete
panels to raise the gauge space instead of paving over.
Myth: Ballasted track does not allow road
vehicles to run along the track.
Reality: Panels can be used to cover the gauge space and over the
ballast shoulders or by simply paving over, as seen in many grade
crossings around the world.
Slab track uses a slab of concrete or asphalt to
distribute the load on the road bed.
Ballast is not used, hence that it is also referred to as “ballastless
track”.
Slab track requires much less regular
maintenance.
This is the main advantage over ballasted track. Cleaning ballast and
tamping is not required. Rail grinding and rail replacement are still
required.
Track in a station in Rheda, Germany. Photo from 2007. Source.
Slab track is permanent (in as much as an engineered
way for transportation can be said to be).
According to Freudenstein (2018) Ballastless tracks, the first
slab track was in the passenger train stations of Rheda, Germany, in
1972. As of 2022, it appears to be holding up unscathed.
When the soil is prone to subsidence, prior engineering
can prevent it.
Given that slab track is not easily readjusted, significant subsidence
would require complex corrective action. In soils prone to subsidence,
this can be solved with geotextiles or mixing in a small amount of
cement.
Slab track is suitable for both freight trains and high
speed passenger trains.
See:
Slab track avoids flying ballast.
The air currents created by high speed train operations make some
ballast pieces “fly”. This can hit people or cause cosmetic damage to
trains. A properly designed train will not be damaged by flying ballast.
Slab track entirely avoids flying ballast. However, the same problem can
be solved by mats on top of the ballast.
In practice, slab track is always built with continuously
welded rail.
Jointed rail would defeat the point of building slab track instead of
ballasted track.
Occasionally in bridges rail is fastened directly to a grider under
the rail that runs through the length of the bridge without gaps.
Rail is usually referred to by its linear
mass.
Typical values are around 60 kg/m. Note this is for a single rail, so
the total mass of rail in a track is 2 times as much.
All rail vehicles are compatible with all rail profiles
for general use.
The reasons different rail profiles are used is to vary the linear mass
and within the same linear mass, as a microoptimization of running
characteristics.
Standard rail profiles.
Modern use is Vignole (T-shaped) rail. This is a family of rail profiles
that are modified I-beam. The wide foot provides support against the
rail itself overturning from the wheel contact force, especially in
curves. The head provides a surface resilient to the very high wheel
contact force. The web increases second moment of area, therefore making
the rail spread the wheel contact forces among several sleepers.
For technical drawings of standard rail profiles see https://rails.arcelormittal.com/types-rails/transport-rails.
The international standard for rail is UIC 860: Technical
specification for the supply of rails.
The European standard for rail is EN 13674-1 Railway applications
- Track - Rail - Part 1: Vignole railway rails 46 kg/m and
above.
Rail inclination.
In common practice, rail is inclined towards the gauge. Inclination
(rise/run) varies between 1/40 (≈ 1.43°) and 1/20 (≈ 2.86°).
-
Corrugation and rail grinding.
As a result of passage of train, rail becomes corrugated. This is caused
by oscillations in the contact force from the wheels. Corrugation is
removed by grinding the face of the rails. Although this removes some
material, it restores the rail profile and prolongs the rail
life.
Railway containment systems keep the rail vehicles close to the track
in case of derailment. This reduces the damage to both the train and the
surroinding infrastructure.
Electric locomotives are cheaper, more powerful and more
efficient than diesel-powered locomotives. However, they require
electrified track.
Electric power can be conveyed by an overhead wire called a
catenary or by a third rail. In both cases, the running rails
are used to close the circuit.
Third rail is only used for urban passenger
transport.
The standard for overhead electrification is AC,
25 kV, mains frequency (50 Hz or 60 Hz).
Obsolete low-frequency AC.
A few obsolete systems at low-frequency AC remain.
These should be converted to the standard 25 kV,
mains frequency. The largest such system is 15 kV at 16.7 kHz
used in central Europe and Sweden. These systems date from the era
before power electronics, when commutator motors were used. Nowdays,
they are a technical burden since they require bigger transformers in
locomotives, converter stations or a separate power grid and have no
advantage.
Sections and phase alternation.
The classical way to try to balance the load among phases is to divide
the catenary in sections. Each section is several kilometres long and
connected between different phases. This reduces but does not eliminate
the phase unbalance, since each section can have diferent amount of
locomotives drawing different amounts of power and moreover this changes
quickly.
Neutral sections.
With phase alternation, there must exist neutral (dead) sections between
energized sections. If sections with different phases contacted, that
would be a short-circuit. Locomotives are unpowered while they traverse
neutral sections, relying on inertia to keep going.
Co-phase system.
A better way to solve unbalance is the co-phase system. The co-phase
system has the whole railway electrified at the same phase. Power
electronics in each traction substations convert the single-phase
railway load to a balanced 3-phase load to the electric transmission
network.
See Co-phase
Traction Power Supply with Railway Hybrid Power Quality
Conditioner.
Shunting is also known as switching, classification and
marshalling.
All current methods involve a shunting bowl.
Container sizes.
World-wide, containers are used in 12 m (40 ft) and 6 m (20 ft). 12 m
containers are the mainstay of international intermodal shipment. 6 m
containers are used for more dense loads. Typically, loaded 6 m
containers are as heavy as loaded 12 m containers despite having half
the volume.
In North America in addition to the above, 16 m containers (53 ft)
are used for shipments that do not go to sea. 17 m containers (60 ft) of
Canadian Tire are occasionally seen in Canada. All of these are
wider than 12 m containers.
Well cars.
In North America and Australia containers are usually transported in
well cars. Typicaly these are 3 units long for 16 m containers and 5
units long for 12 m containers. Single unit well cars almost always are
capable of carrying 16 m containers. Most well cars are made by Greenbrier. In the past, Thrall also
was an important manufacturer.
Center of gravity.
According to the AAR:
The COG for a double-stack car and the load in the platform must be
less than or equal to [2.489 m] at top of rail.
Source: The load
planning problem for double-stack intermodal trains.
Triple stack.
India experimented with shorter than usual intermodal containers and
stacked 3 on top of a flat car (source).
This was not adopted for operation. See https://dfccil.com/ for more information on intermodal
trains in India.
There are railways built with a much broader gauge for specific
applications. For example: The Krasnoyarsk ship
lift with a gauge of 9 m.
Details relevant to rail modeling.
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