What is “TGV” ?

TGV

TGV
TGV
TGV

The TGV is France’s high-speed rail service, operated by SNCF Voyages, the long-distance rail branch of SNCF, the national rail operator.

It was developed during the 1970s by GEC-Alsthom and SNCF. Originally designed to be powered by gas turbines, the prototypes evolved into electric trains with the petrol crisis of 1973. Following the inaugural service between Paris and Lyon in 1981 on the LGV Sud-Est (LGV (French: Ligne x Grande Vitesse, high-speed line)), the network, centred on Paris, has expanded to connect many cities across France and in adjacent countries on both high-speed and conventional lines.

The commercial success of the 1st LGV, the LGV Sud-Est, led to an expansion of the network to the south, and new lines in the west (LGV Atlantique), north (LGV Nord) and east (LGV Est). Eager to emulate the success, neighbouring countries such as Belgium, Italy, Spain and Germany built their own high-speed lines. TGVs link with Switzerland, Italy, Germany and Belgium; with Belgium, Germany and the Netherlands through the Thalys network; and the Eurostar network links France and Belgium with the United Kingdom. Several lines are planned, including extensions within France and to surrounding countries. Cities such as Tours have become part of a “TGV commuter belt” around Paris.

In 2007, SNCF generated profits of €1.1 billion driven largely by higher margins on the TGV network.

The idea of the TGV was 1st proposed in the 1960s, after Japan had begun construction of the Shinkansen in 1959. At the time the French government favoured new technology, exploring the production of hovercraft and the Axrotrain air-cushion vehicle. Simultaneously, SNCF began researching high-speed trains on conventional tracks. In 1976, the government agreed to fund the 1st line. By the mid-1990s, the trains were so popular that SNCF president Louis Gallois declared TGV “The train that saved French railways”.

It was originally planned that the TGV, then standing for trxs grande vitesse or turbine grande vitesse (high-speed turbine), would be propelled by gas turbines, selected for their small size, good power-to-weight ratio and ability to deliver high power over an extended period. The 1st prototype, TGV 001, was the only gas-turbine TGV: following the increase in the price of oil during the 1973 energy crisis, gas turbines were deemed uneconomic and the project turned to electricity from overhead lines, generated by new nuclear power stations.

In 1976 the French government funded the TGV project, and construction of the LGV Sud-Est, the 1st high-speed line, began shortly afterwards. The line was given the designation LN1, Ligne Nouvelle 1, (New Line 1).

After two pre-production trainsets had been tested and substantially modified, the 1st production version was delivered on 25 April 1980.

The LGV opened to the public between Paris and Lyon on 27 September 1981. Contrary to its earlier fast services, SNCF intended TGV service for all types of passengers, with the same initial ticket price as trains on the parallel conventional line. To counteract the popular misconception that the TGV would be a premium service for business travellers, SNCF started a major publicity campaign focusing on the speed, frequency, reservation policy, normal price, and broad accessibility of the service. This commitment to a democratised TGV service was enhanced in the Mitterrand era with the promotional slogan “Progress means nothing unless it is shared by all”. The TGV was considerably faster than normal trains, cars, or aeroplanes. The trains became widely popular, the public welcoming fast and practical travel.

High speed lines based on LGV technology connecting with the French network have been built in Belgium, the Netherlands and the United Kingdom.

On 28 November 2003 the TGV network carried its one billionth passenger, 2nd only to the Shinkansen’s five billionth passenger in 2000.

Excluding international traffic, the TGV system carried 98 million passengers during 2008, an increase of 8 million on the previous year.

LGVs can incorporate steeper gradients than normal. This facilitates planning and reduces their cost of construction. The high power/weight and adhesive weight/total weight ratios of TGVs allow them to climb much steeper grades than conventional trains. The considerable momentum at high speeds also helps to climb these slopes very fast without greatly increasing their energy consumption. The Paris-Sud-Est LGV has grades of up to 3.5%. On a high-speed line it is possible to have greater superelevation (cant), since all trains are travelling at the same (high) speed and a train stopping on a curve is a very rare event. Curve radii in high-speed lines have to be large, but increasing the superelevation allows for tighter curves while supporting the same train speed. Allowance for tighter curves can reduce construction costs by reducing the number and/or length of tunnels or viaducts and the volume of earthworks.

Track alignment is more precise than on normal railway lines, and ballast is in a deeper-than-normal profile, resulting in increased load-bearing capacity and track stability. LGV track is anchored by more sleepers/ ties per kilometre than normal, and all are made of concrete, either mono- or bi-bloc, the latter consisting of two separate blocks of concrete joined by a steel bar. Heavy rail is used and the rails are more upright, with an inclination of 1 in 40 as opposed to 1 in 20 on normal lines. Use of continuously welded rails in place of shorter, jointed rails yields a comfortable ride at high speed, without the “clickety-clack” vibrations induced by rail joints.

The diameter of tunnels is greater than normally required by the size of the trains, especially at entrances. This limits the effects of air pressure changes, which could be problematic at TGV speeds.

LGVs are reserved primarily for TGVs. One reason for this is that capacity is sharply reduced when trains of differing speeds are mixed. Passing freight and passenger trains also constitute a safety risk, as cargo on freight cars could be destabilised by the air turbulence caused by the TGV.

The permitted axle load on LGV lines is 17 t, imposed to prevent heavy rolling stock from prematurely damaging the very accurate track alignment required for high-speed operation. Conventional trains hauled by locomotives are generally not allowed, since the axle load of a typical European electric locomotive exceeds 20 t. Freight trains are generally not permitted except for mail trains run by the French postal service, using specially adapted TGV rolling stock. TGV power cars, the lightweight streamlined locomotives at both ends of TGV trainsets, are within the 17 t limit, but when the double-deck TGV Duplex trains were introduced in the 1990s special design efforts were needed (a ‘hunt for kilograms,’ chasse aux kilos) to reduce weight to ensure that they conformed to the 17 t limit.

The steep gradients common on LGVs would limit the weight of slow freight trains. Slower trains would also mean that the maximum track cant would be limited, so for the same maximum speed a mixed-traffic LGV would need to be built with curves of even larger radius. Such track would be much more expensive to build and maintain.

Some stretches of less-used LGV are routinely mixed-traffic, such as the Tours branch of the LGV Atlantique and the planned Nxmes/Montpellier branch of the LGV Mediterranxe. The British High Speed 1 from the Channel Tunnel to London has been built with passing loops to support freight use, but this facility is used infrequently.

Maintenance on LGVs is carried out at night, when no TGVs are running.

LGVs are fenced to prevent trespassing by animals and people. Level crossings aren’t permitted and overbridges have sensors to detect objects that fall onto the track.

All LGV junctions are grade-separated, the tracks crossing each other using flyovers or tunnels, eliminating crossings on the level.

Because TGVs on LGVs travel too fast for their drivers to see and react to traditional lineside signals, an automated system called TVM, “Transmission Voie-Machine” is used for signalling. Information is transmitted to trains by electrical pulses sent through the rails, providing speed, target speed, and stop/go indications directly to the driver via dashboard-mounted instruments. This high degree of automation does not eliminate driver control, though there are safeguards that can safely stop the train in the event of driver error.

Two versions, TVM-430 and TVM-300, are in use. TVM-430 was 1st installed on the LGV Nord to the Channel Tunnel and Belgium, and supplies trains with more information than TVM-300. Among other benefits, TVM-430 allows a train’s onboard computer to generate a continuous speed control curve in the event of an emergency brake activation, effectively forcing the driver to reduce speed safely without releasing the brake by displaying the Flashing Signal Aspects on the speedometer. When the flashing signal is displayed, the driver must apply the brake and target speed will be more constrained at the next block section.

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