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 TGV Basics

TGVweb > Introduction > TGV Basics

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The TGV (Train à Grande Vitesse) is the French high speed train. Of course, there is no such thing as the TGV; there are many significant differences among the 350-odd trainsets in service today, and the name TGV refers to much more than just the trains. Indeed, the TGV is a system which comprises train, track, and signalling technologies that when combined make high speeds (typically 300 km/h, or 186 mph) possible. The TGV system is owned and operated by SNCF, the French national railways, and is an integral part of French rail travel.

Historical Overview

The TGV program was launched in the late 1960s. In its early stages, the program was considered a technological dead end. Conventional wisdom at the time held that steel wheel on steel rail technology had been explored and understood to its fullest, and it was time to move on to more innovative technologies like magnetic levitation and jet-powered hovertrains. As a result, the project did not originally receive any government funding.

SNCF's idea for the TGV was to develop a high speed rail system that remained compatible with the existing railway infrastructure. This had the important benefit of allowing high speed trains to use existing facilities in the heart of many cities, where building any new tracks or stations would have been prohibitively expensive. Another advantage was the possibility of running TGV trains to many destinations over existing trackage, after a high speed dash on a dedicated trunk line. Clark Kent on conventional track, and Superman on special dedicated track. Finally, having a high speed rail system that fully integrates into the existing rail network makes it possible to build new high speed lines gradually, opening them section by section.

The first prototype train, the TGV 001, started an extensive testing program in the early 70's. The TGV 001 (photo by Jean-Paul Lescat) was powered by a gas turbine, and on 8 December 1972, it set the world speed record for a train in autonomous traction, at 318 km/h (198 mph). This record still stands, 23 years later. (The world's fastest diesel train is a Russian TEP80 locomotive, with 273 km/h (147 mph). The TGV 001 made more than 175 runs at speeds in excess of 300 km/h (186 mph) and along with other prototype trains provided valuable engineering data for the development of the production TGV. A more detailed history can be found elsewhere in these pages.

A completely new line was built beginning in the late seventies, running from Paris most of the way to Lyon. On 27 September 1981, the first section of the line was opened to revenue service by president François Mitterrand, and the streamlined, bright orange trains became instant celebrities. It helped that just a few months before, one of the new trainsets had smashed the world speed record (held since 1955 by a pair of French electric locomotives) with a run at 380 km/h (236 mph).

The new TGV was incredibly successful, and gutted the Paris-Lyon airline business. It became one of the few parts of SNCF that turned a significant profit, and completely payed for itself (including construction costs) in only a decade. The French government, faced with this success, hailed the new system and offered its backing for further development of the nascent high speed rail network. The TGV had become a technological symbol associated with France.

Since then, new TGV lines and trains have been built, and improvements made with each generation. In 1989, the TGV Atlantique made its debut, serving points west of Paris. The trains incorporated many improvements over the earlier Sud-Est generation, a sign of the continuing research and development being conducted by SNCF and its contractors. Most notably, the 1981 record was pushed to 515.3 km/h (320.3 mph) on 18 May 1990, using the newer generation equipment. This is also the subject of other documents in these pages.

Today, there are three major trunk lines radiating out of Paris, the most recent one being the Nord-Europe line, opened in 1993 and connects Paris to Lille, Belgium, the Netherlands, Germany, and Britain through the Channel tunnel. Extensions continue to be built, although budgetary constraints have slowed the momentum of the TGV expansion.

TGV technology has been a contender in many export ventures, to Spain (operating), South Korea (under construction), the United States (awarded), Taiwan (awarded), China, etc. TGV trains now visit many parts of Europe, including Germany, Britain, Italy, Belgium, the Netherlands, and Switzerland.

What Makes the Train Special?

Looking at the train itself, the most striking aspect, to the newcomer, is the aerodynamic styling of the nose. But that is not where the innovation lies. Perhaps the most interesting feature of a TGV trainset is its articulation. The cars are not merely coupled together; instead, they are semi-permanently attached to each other, with the ends of two adjacent cars resting on a common two-axle truck. It is thus more appropriate to speak of 'trailers' than of 'cars'.

There are several good reasons for this design. Perhaps the most obvious is that the TGV was designed from the beginning to be a very lightweight train; even with an axle load limit of only 17 metric tons, it made sense to reduce the number of axles. Placing the wheels between the trailers also reduces interior noise levels, provides more space and a higher plane for the suspension, and improves aerodynamics (due to the lower height and small inter-trailer gaps). Articulation of the train also allows adjacent trailers to be dynamically coupled by dampers, and makes possible a clean, quiet passage from one trailer to the next. Articulation has also proved to be an important safety feature, preventing TGV trains from jack-knifing in a collision as a conventional train might.

TGV trainsets are essentially symmetric and reversible, with a locomotive, also called power unit or power car, coupled at each end. the trailing power unit collects power from the overhead electric catenary, and feeds power to the leading power unit through a cable running along the roof of the train. This single-pantograph arrangement prevents one pantograph from disturbing the wire and thus disrupting the contact for the following pantographs. The pantographs themselves are among the most sophisticated, some featuring active damping.

The brakes are suited for running at high speed. They are capable of dissipating a very large amount of energy. The locomotives each have dynamic brakes, in addition to brake shoes for emergency stops. The trailers are equipped with four disks per axle, and in some cases backup brake shoes. Future models might include magnetic induction track brakes.

Another innovation in the TGV system is the exclusive use of in-cab signalling for high speed running. TGV lines do not have lineside signals; they are too difficult to read at speed. All signalling information is transmitted to the train through the rails, and appears to the engineer in the cab. In general, TGV trainsets are heavily computerized, and many important functions are controlled digitally.

What Makes the Tracks Special?

Dedicated TGV lines use no special technology-- just welded rails laid on hybrid steel and concrete ties, over a thicker than usual bed of ballast. The greatest difference lies in the combination of curve radii and superelevation that make high speed possible; a 5 km (3 mi) radius would be considered tight. The track centers are spaced further apart than usual, to reduce the blast of two crossing trains. Signalling blocks measure 1500 m (5000 ft) and certain lines allow one train every three minutes. The catenary is of completely standard design, essentially identical to 25 kV equipment on other French lines. The track and catenary are aligned and tuned specially for high speed.

Safety, as usual in railways, is a top concern. High speed lines are completely fenced off, and grade separated. Rolling stock is maintained in top condition. The TGV safety record speaks for itself; there have been no casualties in 17 years of daily operation at speeds up to 300 km/h (186 mph). That is not to say there have not been incidents... The most spectacular of which was the December 1993 derailment of a TGV-Réseau trainset, at a speed of 294 km/h (183 mph). This, and all other major incidents, are detailed elsewhere in these pages.

More background about the TGV and its context in railway history can be found in the Encyclopedia Britannica.

What's in TGVweb

For more specific information regarding the various aspects of the TGV program as described above, go back to the table of contents and select the topic you wish to explore in more depth.

TGVweb > Introduction > TGV Basics

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