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.
1 Track
Track supports the weight of the train and guides it. All types of track are support structures for steel rails.
1.1 Gauge
Gauge is the spacing between the inside face of rails.
The exact gauge is a result of historical accident, rather than rationally chosen.
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.
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.
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Narrow gauge is obsolete. Narrow gauge railways are like normal railways, except they suck. They have less carrying capacity and less stability for no real benefit. It has been claimed that narrow gauge track is more suited for tight curves. However, standard 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 trucks or independently rotating wheels, not using a non-standard gauge.
All existing narrow gauge railways should be converted to standard gauge.
Standard 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.
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.
Standard gauge is wide enough.
The “ideal” gauge is often thought by railway engineers to be slightly wider than today’s standard gauge, roughly around 1676 mm. Nonwithstanding with that, standard gauge is not “too narrow”. 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 gauge”
Instead, the limiting factor in the capacity of wagons is the loading gauge and axle load rating. The Britain-France tunnel shuttle train has one of the widest loading gauges, at > 4 m and runs on standard gauge.
1.2 Axle load rating
Typical axle load ratings as of 2023:
North America: 319 kN (32.5 t)
Western Europe: 221 kN (22.5 t)
Russia, Belarus, Ukraine, etc. (CIS): 230 kN (23.5 t)
1.3 Ballasted track
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.
1.3.1 Sleepers
Concrete sleepers are the most common.
They are made of concrete with prestressed longitudinal reinforcement bars.
Steel sleepers are occasionally used.
They are much lighter than concrete sleepers. They have more possibility of corrosion.
Although wood sleepers are obsolete, they are still found in some old tracks.
In Mexico, uniquely in railways, some tracks use a regular mix of concrete and wood sleepers.
Example: In this video is visible a patter of 6 concrete sleepers followed by 6 wood sleepers. This is done for lack of budget to upgrade the whole track to concrete sleepers.
1.4 Slab track
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.
1.4.1 Types of slab track
Embedded sleepers/hemisleepers.
Concrete is poured around the sleepers. The sleepers effectively become one with the pour.
Continuously-supported.
There are no sleepers. The rail foot and part of the web is embedded in a continuous support of elastomer, which is in turn embedded in the concrete slab.
Occasionally in bridges rail is fastened directly to a grider under the rail that runs through the length of the bridge without gaps.
1.6 Rail
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.
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.
Type 1. Installed between rails. Contacts derailed wheels.
Type 2. Installed outside of rails. Contacts derailed wheels.
Type 3. Installed outside of rails. Contacts derailed trucks at the axle level.
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.
All track should be protected by derailment containment. However, mediocre practice usually limits it to bridges. Derailments are especially problematic on bridges because the train can fall over the sides or hit and damage structural elements. The latter also applies to tracks under bridges.
Open deck: The sleepers are supported directly by the bridge.
Closed deck: Any track construction method can be used. Ballasted or slab track.
Direct attachment: Sleepers are not used.
In open deck bridges with ballasted track, superelevation can be given by difference in height of the bridge members that support it, shims above or below sleepers, by wedge-shaped sleepers or different daping on each side.
1.10 Tramway track
Minimum radius of curve.
To fit around and on existing infrastructure, especially roads, tramways are constructed with much sharper curves. According to Esveld (Modern Railway Track, Esveld 2001, p. 228) Roughly, curves as sharp as 25 m radius are allowed. For vertical curves, a minimum of 1000 m is recommended.
2 Rail vehicles
Height in rail vehicles is always from the top of the rail.
The only part below 0 mm height is a part of the flange of the wheels.
Hanging equipment.
Apart from the wheel flanges, any part of a rail vehicles below top-of-rail height is anomalous and called “hanging equipment”. Hanging equipment detectors signal (usually by radio) their presence.
Loading gauge height.
In North America, railway wagons are up to 6.17 m high. The only wagons to reach this height are some autoracks and well cars loaded with 2 hi-cube containers.
Greater Freigher wagons in Australia (the 3 wagons after single passenger wagon) Source.
Greater Freigher boxcars.
In Australia, some boxcars are approx. 5.7 m tall (visual estimation), higher than North American F plate boxcars. These are called “Greater Freighter”. See https://youtu.be/niCBcVdcYuE?t=632.
“ton” rating of North American bogies
The US-American, stupid as they are, label train bogies (trucks) in a counterintuitive way. The “ton” rating is supposed to be the max. net load of the wagon, assuming it uses 2 such trucks. None of the max. weight in a wagon, bogie, axle or wheel equals the “ton” rating.
Most rail wagons use bogies with 914 mm wheels. Articulated well cars use bogies with 965 mm wheels between articulated sections, and with 914 mm wheels in the ends.
US-American bogie name
Axle load
Wheel diameter
100 ton
319 kN (32.5 t)
914 mm
125 ton
350 kN (35.7 t)
965 mm
2.1 Couplers
Couplers are the devices at the end of rail vehicles that join it with the previous and/or next vehicle in the same train.
DAC4EU.
The DAC4EU project intends to replace the screw coupler used in Western Europe with Scharfenberg couplers. It has the medium-term goal of enabling automatic pneumatic, electrical and digital connections and automatic uncoupling.
The research project was intended to be completed by early 2023. However, as of January 2023, it is overdue.
2.2 Bogies
Bogies are called steering when they are able to steer the axles (making them non-parallel) to better follow the track in curves.
Myth: Steering bogies actively steer.
All steering bogies used in freight railways are passive. That is, they contain no motors, pistons or actuators regarding steering. They merely allow the natural steering motion of axles, which is given by wheel conicity. A steering force exists in all bogies in curves, but this only leads to steering movement in specially designed bogies.
EMD steering bogies are described in the following references (non-exhaustive list). They were developed starting in the 1980s by David Jason Godling et al., who has commented in forums about them. Note that the patents are for different stages of development:
Loading gauges are given as width × height. This refers to the maximum width and height. Note that the loading gauge is usually not rectangular, but instead it tapers near the top (for tunnels) and the bottom (for platforms).
Region
Max. width (mm)
Max. height (mm)
North America
3251
6172
Russia and ex-USSR
3400
5300
India
3660
?
Loading gauge in North America goes up to 3.251 m × 6.147 m.
Extrapolating from experience in narrow gauge railways, Collins (1932) suggests that width can be up to 3 times the track gauge and height up to 4 times the track gauge. On standard track gauge, this gives 4.3 m × 6.5 m. This height is remarkably close to the maximum height of North American loading gauge, 6.172 m, used for double stack well cars and some autoracks. The width in North America is lower mostly because it has become entrenched in track spacing, tunnel cross sections and station platforms.
3 Shunting
Shunting is also known as switching, classification and marshalling.
All methods involve a shunting bowl.
Methods:
Flat. This is the most frequent and most straightforward method.
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.
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.
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.
Security.
In Mexico, some train runs are protected by armed guards, especially intermodal trains (example).
Securing containers.
Containers must be secured by twistlocks. In United Kingdom, non-secured containers in single stack have been blown by the wind, while the wagon remained in the track. See The Aerodynamics of a Container Freight Train, p. 4.
Wind turbine blades.
Wind turbine blades are often transported segmented by railway. As of 2023, flexible blades that can bend to follow the curature of the tracks are a possible development. See Flexing the Limits of Land-Based Wind Turbine Rotor Growth. Of course, the complication can be avoided completely by using nuclear energy.
Magnetic suspension is inherently energy-expensive and requires active components, unlike railways.
Switches are very expensive and complex to built.
This makes unfeasible to share tracks among different transport lines in a single station.
Maglev is non-standardized, hindering exchange.
9 Rail modeling
Any rail model can be seen as a model or as a tiny railway on its own right.
Use 1:160 scale (N) or 1:220 scale (Z).
Ignore all scales bigger than 1:160. They are too big to build a realistic model in a reasonable space. Specifically, the curves become too tight by necessity. Rail models are the ideal size to show the engineering of the rial system. 1:87 (HO) is too big for that; it is for toy trains.
Use flex track from the start.
Sectional track constrains design and discourages experimentation.
Instead of benchwork use several off-the-shelf tables put together.
Use body-mounted couplers.
Truck-mounted couplers interfere with the self-aligning mechanism of axles, especially in lengthwise compression of the train. Some model vehicles come with truck-mounted couplers. Replace them with body-mounted couplers.
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