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.
By convention, standard gauge is 1435 mm. It is designated as the standard by the UIC. Here, 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.
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Narrow gauge is obsolete.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.
Typical axle load ratings as of 2023:
Elements.
From top to bottom, the elements of classical railway track are:
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.
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.
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.
Embedded sleepers/hemisleepers.
Concrete is poured around the sleepers. The sleepers effectively become one with the pour.
Technologies:
Non-embedded sleepers/hemisleepers.
There are 2 subtypes:
Technologies:
Direct attachment to slab.
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.
Technologies:
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°).
Rail grinder working. (source).
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.
See also:
Source for the types: Functionality Analysis of Derailment Containment Provisions through Full-Scale Testing—I: Collision Load and Change in the Center of Gravity
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.
Can be open deck or closed deck.
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.
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 |
Type F couplers (source).
Rigid couplers.
Couplers can be:
The family of couplers used in North America includes:
Scharfenberg coupler (source).
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.
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:
General Electric steering bogies are described in the following references (non-exhaustive list):
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.
Loading gauge in India goes up to 3.660 m × 4.750 m (Indian Railways Schedule of Dimensions 1676 mm gauge, p. 23). However, double stack trains are higher.
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.
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.
Kicking.
Videos:
Humping.
Gravity.
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.
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.
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.
Links:
There are railways built with a much broader gauge for specific applications. For example: The Krasnoyarsk ship lift with a gauge of 9 m.
Region | Length | Speed | Electrified? | Typical axle load | Containers |
North America | Very long, ~2 km | Varies widely, from walking speed to ~90 km/h | Generally not electrified | 319 kN (32.5 t) | Double stack well cars |
Western Europe | Short, ≤ 780 m. | Fast | Mostly electrified | 221 kN (22.5 t) | Single stack flat cars |
Russia and ex-USSR | Long, 1.5 km. | Fast | Mostly electrified | 230 kN (23.5 t) | Single stack flat cars |
India | Medium, 1 km. | Fast | Significant electrification | ? | Double stack flat cars |
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.
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.
Details relevant to rail modeling.
Ties are painted white when they are over a drainage pipe.
Ref: Everything to know about the railroad & how to model it
In Russia the railway company builds platforms for train watching: https://www.youtube.com/watch?v=0j9iJMGtqa0.