Over the past 30 years or so,Japan and Europe have in-vested heavily in networks

of high-speed trains to link major cities.They have turned to fast trains, exceed-ing 200 kilometers (roughly 125 miles)per hour, in part to relieve congestionon roads and at airports while minimiz-ing operating costs and pollution.

Of course, for trains to live up to theirfinancial and environmental promise,they must draw high numbers of pay-ing passengers. The Japanese and Euro-pean experience has shown that railwayscan often meet that demand if the rides

are comfortable, competitively pricedand able to deposit travelers at their des-tinations about as quickly as an airplanewould. Aircraft still go much faster thantrains, often exceeding 600 kph, butlong travel times to and from airportsoften cut significantly into time savings.

Engineers knew as early as the 1950sthat simply by using more power theycould force some conventional trains toreach 331 kph, much faster than the130-kph top speed of many Americanlong-distance trains today. But the high-er speeds were deemed infeasible forcommercial application because the fast-

moving vehicles damaged the tracks se-verely. High-speed trains, it seemed,would have demanded extensive, andthus prohibitively expensive, track main-tenance efforts.

Nevertheless, Japanese and Europeaninnovators soon found ways to exploitexisting technology to improve speedsto about 200 kph between some cities.For instance, without altering the trainsthemselves greatly, the Japanese design-ers achieved gains by such maneuvers asbuilding tracks that avoided tightcurves and steep grades. The huge pop-ularity of their original Shinkansen, or

How High-Speed Trains Make Tracks

In Europe and Japan, train manufacturers are gearing up to achieve ultrafast speeds routinely,

without relying on levitation

by Jean-Claude Raoul

100 Scientific American October 1997 How High-Speed Trains Make Tracks

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TRAIN À GRANDE VITESSE (TGV), shown in its double-decker (duplex) version, runs at up to 320 kilometers (almost

200 miles) per hour in France. The map displays the EuropeanCommunity’s master plan for a high-speed train network.

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bullet train, which began operation in1964 between Tokyo and Osaka,sparked new interest in overcoming thetechnological obstacles to operating rou-tinely at still higher speeds.

Those efforts have since resulted in anumber of trains that go significantlyfaster than 200 kph. Among the best-known examples are the Train à GrandeVitesse (TGV) series in France, the In-terCity Express (ICE) lines in Germanyand the Eurostar trains (linking Parisand Brussels with London by way of theEnglish Channel Tunnel (“Chunnel”).These trains and newer generations ofthe Shinkansen can all zoom at or near300 kph on dedicated high-speed tracks(although they go more slowly on oldertracks). And plans are under way at theFrench National Railway and at GECAlsthom, respectively the owner andbuilder of the TGVs, to produce anoth-er series of trains—dubbed the “newgeneration”—able to cruise regularly at

360 kph. These vehicles are the productof an intensive research effort involvingabout 50 university laboratories, mostlyin France but also in the U.S., Belgiumand Sweden.

Stability Is Critical

Reaching these milestones has re-quired innovation in all aspects of

railroad engineering, including the de-sign of tracks and signaling systems. Forinstance, as speeds rose, roadside signalsbecame useless for the drivers; the cabswent by the signals too fast. The trainsare now run with guidance from on-board computers that collate informa-tion emitted from monitoring and con-trol equipment in the tracks and in theindividual cars and from dispatchingstations; the computers can also forcethe train to stop if critical safety com-mands go unheeded. But some of themost interesting inventions have altered

components of the trains themselves.The design elements that the French

have introduced for the TGVs offer anexample of the kinds of technology thatmake wheel-on-rail travel at high speedspossible. Those solutions differ in somerespects from those chosen in othercountries, but they provide a sense ofthe work that has allowed speeds to in-crease steadily since the 1960s.

High-speed or not, most long-distancetrains have certain features in common.They are moved by one or two locomo-tives, cars containing the power-gener-ating equipment. This equipment con-verts energy from onboard fossil fuel orfrom an electrical feed into the specificform needed to move the train. In theU.S. many trains still run on diesel fuel.But in Europe most trains, and all high-speed trains, run on cleaner electricalpower; this power is usually drawn fromoverhead lines, or catenaries, through apantograph—a conducting rod—pro-

How High-Speed Trains Make Tracks Scientific American October 1997 101

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truding from the top of thetrain. The energy that is pro-duced allows traction mo-tors under the locomotivesto rotate the axles that joinpairs of driving wheels—

those that grip the track (usetraction) to propel the trainforward.

The driving wheels, as wellas other wheels that simplycarry the weight of the trainand allow it to move smooth-ly along the tracks, reside insupport structures known asbogies. Bogies, also calledtrucks, consist of two or morepairs of wheels and theiraxles connected by a framethat supports the cars above.A suspension system linkingthe bogies and the cars holdsthe cars in place and cush-ions riders from vibrations.

When train speeds rise, thevibrations produced by con-tact between the wheels and the rails in-crease dramatically. These vibrationscan cause the bogies to become ex-tremely sensitive to imperfections in thetrack, to sway from side to side and, ul-timately, to jump the track. Moreover,as the 1950s tests showed, such rockingcan damage the rails and incur hugemaintenance costs. Hence, increasingride stability became an early priority.

In the early 1970s, when scientists atthe French National Railway and GECAlsthom first began aiming for speedsabove 200 kph, powerful computersimulation tools were not available. Butexperimentation and calculation indi-cated that increasing the distance be-tween axles in the bogies to three metersfrom the 2.5 meters of conventionaltrains would maintain stability even atspeeds in excess of 300 kph. Moreover,lengthening the distance would obviatethe need for adding a great deal of vi-bration-dampening equipment thatwould have to be monitored constantlyand replaced periodically.

Suspending traction motors from thebottom of the locomotive or passengercars, instead of mounting them as usualon the bogies, improved train stabilityas well. As bogies get heavier, the risk of

bogie instability and derailment increas-es. Moving the motors off the bogieslowered the weight of the trucks. Todayresearchers at GEC Alsthom, where Iam technical director, continuously testnew materials for the bogies—such asaluminum alloys or carbon fibers—look-ing for substances that will further re-

duce weight while retaining strength.In a key departure from conventional

construction, the designers of the TGVsalso altered the placement of the bogies.Most trains allot two bogies to each car,setting them some distance in from theends of the car. But with the exceptionof locomotives, TGV cars share bogies.

How High-Speed Trains Make Tracks102 Scientific American October 1997

HIGH-SPEED TRAINS operating in Japan and Germany are known, respectively, as theShinkansen, or bullet train (left), and the InterCity Express, or ICE (right). The commercial

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We fit one bogie between each car, sothat an individual car has a total of justone bogie (half a shared bogie at oneend, plus half at the other end). Thesebetween-car trucks knit adjacent carstogether semipermanently, preventingthem from pivoting away from one an-other on curves.

This tight coupling of all cars limitsmanagerial flexibility to an extent; carscannot be added or removed readily toadapt to changing passenger loadsthroughout a day. But such changes areinadvisable in any case, because thecomputer systems that monitor andcontrol every car on the train wouldhave to be reprogrammed constantly toaccommodate the rearrangements—aprocess that would require a great dealof labor and care.

The design of the suspension systemalso influences stability, and so investi-gators have tested several types. If sta-bility were the sole concern, the idealsystem would totally prevent cars from

swaying, but such a suspension wouldcause riders to feel every vibration un-derneath them. For the first generationof TGVs—running between Paris andLyon—engineers settled on a steel-springsuspension, in which the vertical springsbecome stiffer as the frequency of thevibration increases. Those trains beganoperation in 1981 at 270 kph and laterset a speed record when a test showedthey could accelerate to 380 kph.

Later we switched to a pneumaticsuspension: air cushions take the placeof some of the steel springs and providebetter insulation from vibrations. Thisnew suspension, in addition to makingfor a more comfortable ride, helped thesecond generation of TGVs—the Atlan-tique trains, serving areas west of Paris—to set a world speed record of 515.3 kphin 1990 and to operate commercially at300 kph.

In Germany, Sweden and other plac-es, the problem of stability is being ad-dressed somewhat differently than in

France. For instance, instead of alteringthe placement of the bogies, variousmanufacturers install tilt technology tocope with curves: the cars can pivot onthe bogies and lean to balance the forc-es acting on the train and on passengers.Tilt technology has allowed trains to goas fast as 220 kph on upgraded oldertracks, without forcing newer, straighterones to be built.

Optimizing Shape and Weight

In addition to ensuring that high-speed trains will be stable, designers

have to minimize the amount of fuel re-quired to run the vehicles, both to limitpollution from the power plant thatprovides the electricity and to save onthe costs of that electricity. To achievethe greatest speed for the lowest cost,the vehicles, above all, have to be aero-dynamically designed to minimize theamount of drag that is produced whenthey race down the track. For that rea-son, high-speed trains as a group havesmoother surfaces and fewer anglesthan standard trains do.

To reach speeds of 360 kph, more de-sign changes will be needed. Diverseanalytical tools—including sophisticatedcomputer simulation programs, scale-model tests in wind and water tunnels,and analyses of wind flow around full-size trains on tracks—all show that mostof the drag impeding the forward mo-tion of current high-speed trains derivesfrom the bogies and other equipmentunder the frame. Future generations ofTGVs will therefore have smoother un-derframe contours.

Although some people might suspectthat a train’s weight would affect fuelconsumption as much as its shapewould, weight actually has little influ-ence on that aspect of the operation ofhigh-speed trains. But a heavy trainstresses the tracks more than a lighterone does and consequently increasesmaintenance costs. Therefore, to pro-tect the tracks, fast trains need to weighas little as possible.

The novel arrangement of the bogiesin TGVs helps to keep down the weight;by providing one bogie per passengercar instead of two, we almost halve thenumber of bogies in the train. We also

How High-Speed Trains Make Tracks Scientific American October 1997 103

success of the first Shinkansen, which began running in 1964, stimulated the later develop-ment of still faster trains, including TGVs, ICEs and subsequent Shinkansen generations.

DUPLEX TRAIN has several features that enable current TGVs to reach high speeds withoutdestroying the tracks. They include aerodynamic styling; lightened materials throughout thetrain, including in the transformer (in the locomotive), the car frames and the bogies; sharedbogies between passenger cars (instead of two bogies per car); use of a single pantograph (in-stead of the many used in other trains); and a pneumatic suspension (detail at left). The bear-er ring in the suspension puts the weight of the cars on the air cushions, and the ball-and-sock-et joint links the cars. The dampers keep the cars aligned with one another and prevent themfrom rotating around their various axes.

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craft the cars from lighter material thanhas been incorporated into convention-al trains. Use of such materials in thepassenger cars has made it possible toproduce double-decker (duplex) vehi-cles that weigh no more than the single-deck Atlantique trains, even though theduplexes boast seats for 45 percent morepassengers. Thanks to aerodynamicstyling, the duplexes also run as fast astheir one-level counterparts but con-sume less energy.

The motors directly responsible forturning the driving wheels—the tractionmotors—have been lightened, too, with-out sacrificing power. The first TGVswere equipped with motors that eachproduced 535 kilowatts of power; thesecond generation uses motors that gen-erate 1,100 kilowatts. Motors on thefaster, new-generation trains will eachput out 1,100 kilowatts but will be 40percent lighter than the latest TGV mo-tors. These weight reductions have beenachieved by design changes as well asby using lighter materials.

On a per-seat basis, the TGVs areamong the lightest trains in the world,but researchers continue to examine allparts of the train for other ways to re-duce the load on the tracks. For exam-ple, transformers, which convert elec-tricity of different power levels into volt-ages and frequencies required by thetrain’s motors, are among the heaviestparts of the train. By building transform-ers from cobalt-alloyed steel and alu-minum sheets instead of from copperwires, we have recently brought themass of those devices down to 7.5 met-ric tons from 11 metric tons.

New-generation trains will carry thelighter transformers. They will also saveon the weight of their electronic equip-ment, through use of a compact new de-vice known as an insulated gate bipolartransistor. Such transistors will precise-ly control the electricity delivered to thetraction motors. This is the first timethis kind of transistor has been used toproduce such high-power outputs. Wehave put a lot of work into the seats as

well. To save a few kilograms per seat,those in new-generation TGVs will bemade of carbon fibers, magnesium andcomposites.

Stop Smoothly, Go Quietly

Innovations that encourage high speedshave to be accompanied by technolo-

gies that enable the train to stop efficient-ly without jolting passengers or derail-ing the train. The first generation ofTGVs employed a disc-braking systemresembling those found in racing cars.It was advanced for its time and quieterthan conventional brakes, but it still re-lied on friction—that is, on somethingpressing on the discs (which themselvesare on the axles) to dissipate kinetic en-ergy and thus stop the rotation of thewheels. Operating such brakes consumesenergy and also causes wear and tear onthe braking components and the bogies.

To save on fuel and on maintenanceexpenses, the newer TGVs complementdisc brakes with state-of-the-art “dy-namic” braking systems. These help tostop the train by converting mechanicalenergy from the traction motors backinto electricity. This electricity can thenusually be recycled—passed to the over-head catenaries for use by moving trainsup or down the line or perhaps to theair-conditioning or to other electricalcomponents of the train. In the new-generation trains the braking system willdissipate some unneeded electricity byfeeding it safely into the tracks as heat.More than 90 percent of the decelera-tion in the new-generation trains willbe achieved through the dynamic brak-ing systems.

None of these innovations would beof any value if manufacturers failed tocontrol the substantial noise generatedby speeding trains. Most of the soundderives from the interaction of wheelsand the rail and from wind passing overand under the train. At high speeds, thesound level increases exponentially. Therise caused by aerodynamic effects is es-pecially huge, proportional to the sixthpower of the speed.

The least noisy shape is the smoothestone, and so we strive to limit edges notonly to reduce drag but to minimize theannoyance to passengers and people wholive near train lines. But not all compo-nents can be made to have smooth con-tours, including the bogies. To cope withthese realities, we shield underframe de-vices with aerodynamic deflectors thatreduce wind resistance.

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WATER-TUNNEL STUDIES of scale-model trains have informed efforts to op-timize the aerodynamic properties of fu-ture TGVs. The relatively straight linesformed by green dye on the model belowmean the model has a good configura-tion. Beyond enhancing speed, an aerody-namic design limits noise. Noise levelsjump abruptly at some critical speed thatvaries for each train but is often in theneighborhood of 300 to 350 kph (graph).

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We also use only one pantograph in-stead of the multiple pantographs foundon more conventional trains. It is situ-ated on the rear locomotive, and a ca-ble brings electricity to the second pow-er unit, at the front of the train. To re-duce noise further, we have redesignedthe pantographs for the new-generationTGVs, giving them fewer edges. TheJapanese, however, have another solu-tion for the pantographs: encasing themin aerodynamic chimneys.

Contact between the wheels and therails contributes to the noise level byproducing vibrations that are capableof exciting both elements. Guided bycomputer simulations, we have nowsubtly altered the design and, in places,the thickness of the wheels to reduce thenoise without increasing their heft; theimproved wheels, which have been test-

ed extensively, will roll on future TGVs.In France, existing high-speed trains

rarely pass through tunnels. But else-where in the world, railroads sometimeshave to be routed through such passage-ways. As the vehicles enter tunnels, theycreate pressure waves that run the lengthof the tunnel and back again at the speedof sound. These waves created by high-speed trains can cause pain to eardrumsand can potentially shatter glass.

Computer simulations and other ex-periments indicate that the intensity ofthe waves can be minimized by chang-ing the shape of the trains, such as giv-ing them a longer nose. Other ways toensure passenger comfort include mak-ing trains airtight and controlling cabinpressure internally. Optimizing the shapeof the tunnel can help as well.

Research on the new-generation trains

has demonstrated that speeds of up to360 kph are technically and economi-cally realistic. And we are already con-structing a locomotive for testing in1999 that will move a full train at 400kph. Indeed, in anticipation of success,track systems under construction inFrance are already being built to handleequipment rolling at that higher rate.Even 400 kph could conceivably bebettered, although whether the fuel re-quired to achieve significantly higherspeeds will be worth the cost is an openquestion.

In Europe, financial considerations arenow slowing the pace at which plannedhigh-speed rail lines are being construct-ed. But building does continue. It seemsreasonable to predict that speeds of 400kph could be commonplace on the newtracks early in the next century.

How High-Speed Trains Make Tracks Scientific American October 1997 105

The Author

JEAN-CLAUDE RAOUL, who joinedGEC Alsthom in 1983, is technical direc-tor of GEC Alsthom Transport in Paris.He is also coordinator for industry andinteroperability of the high-speed net-work in Europe and a member of the sci-entific councils of the Mechanical Labo-ratory of Lille and INRETS, the FrenchNational Research Institute for Trans-portation Systems.

Further Reading

Research Determines Super-TGV Formula. François Lacôte in Railway Gazette Interna-tional, Vol. 149, No. 3, pages 151–155; March 1993.

Europe’s High-Speed Trains: A Study in Geo-Economics. Mitchell P. Strohl. Praeger,Westport, Conn., 1993.

Supertrains: Solutions to America’s Transportation Gridlock. Joseph Vranich. St.Martin’s Press, 1993.

The 21st Century Limited: Celebrating a Decade of Progress. High-Speed Rail/Mag-lev Association. Reichman Frankle, Englewood Cliffs, N.J., 1994.

High-Speed Rail: Another Golden Age? Tony R. Eastham in Scientific American, Vol.273, No. 3, pages 100–101; September 1995.

PRESSURE WAVES, which can cause pain in a passenger’s ears, arise whena train enters a tunnel; the waves travel the length of the tunnel and backagain. Such waves have been measured in computer simulations; red indi-cates the highest pressure, followed by yellow and green. The results of re-cent simulations indicate that long noses on trains can help minimize thewaves, as can certain modifications in the shape of the tunnel itself.

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