Looking down the track at very fast trains

Key text

Some people say we should use 'tilt' trains, which are faster than current Australian trains (but still slow by world standards) and can use existing tracks (Box 1: The centrifugal effect and tilt trains). But most train enthusiasts know that when it comes to real speed, there are only two contenders: the current crop of 'very fast trains' that have wheels and run on steel tracks; and the more imaginative magnetically levitated trains, which excite the mind but are yet to be tested commercially.

How fast is very fast?

The fastest trains in commercial operation today are the French train à grande vitesse (TGV), the Japanese shinkansen  (or bullet train) and the German InterCity Express  (ICE). The TGV routinely travels at 300 kilometres per hour through the French countryside and has been clocked at 515 kilometres per hour in test runs. The bullet train averages 262 kilometres per hour between stations and has recorded 443 kilometres per hour in test runs, while the ICE has a top operational speed of 280 kilometres per hour and has recorded 408 kilometres per hour in trials.

These trains have several things in common:

• They all use electric motors (some very fast trains still run on diesel, but these are slower than their electric counterparts).

• They all have steel wheels that run on steel tracks.

• They have aerodynamic designs to decrease wind resistance - in some ways they look like long, thin aeroplanes without wings.

• They all require special lines to achieve their maximum operating speeds – in particular, these need to be as straight as possible, because very fast trains and tight bends don't mix well (Box 1). Nevertheless, these trains can also run on conventional lines at reduced speeds, a great advantage when approaching major urban centres.

Let's look at one of the most successful of these trains, the TGV, in slightly more detail.

Innovations in the TGV

Many of the innovative aspects of the TGV are in the design and placement of bogies. Bogies consist of two or more pairs of wheels, their axles and a connecting frame that supports the carriages (usually called cars) above. At high speeds, the vibrations produced by contact between the wheels and the rails increase dramatically. This can cause the bogies to sway from side to side, which in turn can damage the track and, in severe cases, derail the train.

While developing the TGV, engineers found that increasing the distance between axles in the bogies could reduce this instability. In addition, since instability increased with increasing bogie weight, they moved the electric motors, usually mounted on the bogies, and suspended them from the bottom of the cars.

Bogie placement was also changed. Conventional train carriages have two bogies each, one towards each end. In the TGV, cars are attached to each other semi-permanently, with the front end of one car and the back end of the next car resting on a common bogie. In this way, each car effectively uses only one bogie (two halves).

Efforts are continually being made to reduce the overall weight of the train, largely because the lighter the train, the less stress there is on the track (therefore lowering maintenance costs). Reducing the number of bogies saves weight. In addition, new, lighter materials are used in the construction of the trains. Even the seats are now made of lightweight carbon fibres, magnesium and composite materials.

Wheels on tracks or levitated

While the TGV, the bullet train and the ICE all use established technology – electric motors and steel wheels – revolutionary technology has produced a high speed train which floats on a magnetic cushion of air above a special track.

Maglev

The maglev differs radically from its more conventional high-speed cousins. It doesn't have wheels and it doesn't run on a steel track. It doesn't even have an on-board motor. The motor that propels the maglev is in the special track, and the propulsion comes from magnets.

In maglev technology, electromagnets (devices that become magnetic when fed an electric current) are mounted on the train and in the track (usually called a guideway). The electromagnets levitate, guide and propel the train along the guideway (Box 2: How the maglev works).

Maglev vs conventional high speed trains

Maglev technology has several theoretical advantages over conventional high-speed trains. Since there is no wheel-to-track contact, less energy is lost due to friction and the trains create less noise. Maglevs also use less energy to achieve the same speed as conventional very fast trains.

In addition, since the motor is in the guideway rather than on the train, it is possible to increase its power on steep sections. This means that maglevs can climb steeper grades than conventional high-speed trains, reducing the need for tunnels.

Despite such advantages, maglevs remain commercially unproven. In comparison, trains like the TGV, the bullet train and the ICE have been formidably successful. Millions of people have travelled on them; hundreds of thousands use them each day. Each new generation of train gets faster, and they boast an impressive safety record.

One of the biggest barriers to maglevs is the need for a whole new infrastructure. Their guideways need to be constructed from scratch, a costly and financially risky venture, at least in the early stages. In contrast, conventional high-speed trains can run on existing tracks through urban areas, and the high-speed portions can be constructed in stages.

Safety of very fast trains

Very fast trains are safe compared to most other forms of motorised transport. For example, the TGV, which commenced operation in 1981, travels about 10 million passenger kilometres each year. It is yet to have an on-board fatality, although a number of people have died in collisions at road crossings.

But this is not to say that major disasters are impossible. In June 1998, an InterCity Express, travelling at about 200 kilometres per hour, derailed near Eschede in Germany, killing 102 people and injuring hundreds more. The cause of the accident is still under investigation.

The future of high speed trains

Commentators seem to agree that very fast trains – the conventional ones, at least – will form a significant part of the international transportation scene in coming decades.

But Australia is something of a special case. With our small population dispersed in relatively small towns and middle-sized cities across vast distances, the commercial viability of very fast trains remains in doubt. There is no shortage of ideas: some people talk of a high-speed train network linking Melbourne to Brisbane (via Canberra), and another, linking Melbourne and Darwin, has also been proposed.

Are we on the cusp of a transport revolution in Australia, or are our trains destined to remain plodders? Should we launch straight into technology, or should we consider the tried-and-true alternatives? Expect the debate to continue, full steam ahead.

Box 1. The centrifugal effect and tilt trains

Similar things will happen if a train takes a bend too fast. Standing passengers will lurch over and luggage may fall down from racks. If the centrifugal effect is strong enough (and it has to be very strong), the train itself might fall off the tracks.

Smoothing out the bends

Train companies wish to avoid disturbing their customers with centrifugal effects, so they adopt strategies for 'smoothing' out the bends and corners that a train inevitably has to take.

The centrifugal effect is proportional to the square of the velocity of the train and inversely proportional to the radius of the bend in the track. This means that if you want to double the velocity of the train but keep centrifugal effects constant, you must increase the radius of the bend four-fold.

Tilting the train

Another strategy for coping with centrifugal effects is to tilt the train itself – this is used, for example, by the Swedish X2000 series that can travel up to 200 kilometres per hour. If the train is tilted, and with it all the tables, seats and passengers, then the tendency for everything to slide down this slope can exactly balance the centrifugal tendency for them to move towards the outer wall of the carriage, and everything feels normal.

The actual tilting of the train is done by pivoting individual carriages on their bogies using pistons. The pistons are controlled by computer and move up or down depending on the strength of centrifugal effect. By counteracting the centrifugal effect in this way, 'tilt' trains can travel up to 40 per cent faster around curves than conventional trains.

Tilting technology was tried in Australia on the Sydney-Canberra line for a 2-month period in 1995. A trip that usually takes 4 hours and 5 minutes on the XPT was reduced to 3 hours and 25 minutes, a timesaving of about 16 per cent. A new tilt train service is to be introduced later this year between Brisbane and Rockhampton. The service should reduce travelling time from 9.5 hours to 7 hours.

Related sites

• Force: Centripetal vs centrifugal (Public Broadcasting Service and Turner Adventure Learning)

• Tilting trains (Oliver Keating)

Box 2. How the maglev works

Levitating the maglev

The attraction or repulsion of electromagnets is used to levitate a maglev. On one breed of maglevs, the Transrapid, levitation magnets fitted to the train are attracted to support magnets on the underside of the guideway. A computer-controlled system ensures that the vehicle levitates – via this attractive force at a constant distance from its guideway. In other words, the two magnets attract each other and thus lift the carriage, but the attraction is not strong enough so that the two magnets make contact with each other. The train therefore 'floats', making no physical contact with the guideway.

Some other types of maglev use the repelling force of magnets with the same polarity to levitate the train. In all types, guidance magnets ensure that the train remains at the appropriate distance from the vertical edge of the guideway.

Propelling the maglev

Electromagnets also propel maglev trains. A series of electromagnets are laid out in a line along the guideway and electromagnets are installed on the train.

An electromagnet on the guideway pulls a train magnet towards it because it has an opposite polarity. As the train passes over the guideline magnet, the polarity of the magnet is reversed so it matches that of the train magnet, thus repelling the train magnet. As the train hurtles along, the electromagnets in the guideway switch on and off and reverse polarity as required. Electric current activates the guideway electromagnets only when the train passes over them.

Related sites

• How maglev trains will work (How Stuff Works, USA)

• Maglevs (magnetically levitated trains) (Oliver Keating)

Activities

• University of Virginia (USA)
  • How things work: Magnetically levitated trains
    Clear answers to a number of questions about magnetism and electromagnets, as well as a few suggestions for related demonstrations.

• How Stuff Works (USA)
  • How electromagnets works: Experiments to try
    

• Jefferson Lab (Southeastern Universities Research Association, Inc and US Department of Energy)
  • Magnets and electromagnets

• Illinois Institute of Technology, USA
  • Magnets, electromagnets and fields of force

• Kyrene School District (Arizona, USA)
  • Magnetic levitation vehicles
    Students design, build and test a magnetic levitation transportation system.

• The European Railway Server
  • TGV card models

Further reading

Useful sites

Describes a variety of very fast trains, including maglevs and tilt trains.
http://www.o-keating.com/hsr/

The TGVweb (European Railway Server)

'Introduction' includes background information, history of the TGV before 1981 and frequently asked questions. 'The future TGV' includes recent TGV research and development.
http://www.railfaneurope.net/tgv/tgvindex.html

Australian very fast trains – a chronology (Australian Parliamentary Library)

Outlines the various proposals to build high speed rail lines in Australia.
http://www.aph.gov.au/library/pubs/bp/1997-98/98bp16.htm

Glossary

polarity. Describes a situation in which there are opposing physical properties at different points in an object or system. When this refers to magnetic poles, the two opposite poles are called ‘North’ and ‘South’; when it refers to electric charges, the two opposite properties are called positive and negative. Unlike poles (and charges) attract; like poles (and charges) repel.

transformer. A device consisting of two coils of wire wound on a soft iron core which is used to change the voltage of an alternating current. Transformers can either increase the voltage (a step-up transformer) or decrease the voltage (a step-down transformer). TV receivers have a step-up transformer that increases the voltage enough to operate the picture tube, and also a step-down transformer to reduce the supply voltage (240 volts) to the 5 volts needed to run transistors.