High-Speed Rail in FranceHigh-Speed Rail in FranceFrance has a large network of high-speed rail lines. As of June 2021, the French high-speed rail network comprises 2,800 km (1,740 mi) of tracks, making it one of the largest in Europe and the world. As of early 2023, new lines are being constructed or planned. The first French high-speed railway, the LGV Sud-Est, linking the suburbs of Paris and Lyon, opened in 1981 and was at that time the only high-speed rail line in Europe. In addition to serving destinations across France, the high-speed rail system is also connected to the United Kingdom, Spain, Belgium, the Netherlands, Luxembourg, Germany, Switzerland, and Italy. The SNCF, France's state-owned rail company, operates both a premium service (TGV inOui) and a budget service (Ouigo). The French national high-speed rail network follows the spoke-and-hub model, centered on Paris. Besides its main operator, the SNCF, it is also used by Eurostar, Thalys, Deutsche Bahn, Trenitalia France, RENFE, and the Swiss Federal Railways. France High-Speed Rail Tracks The newest high-speed lines allow speeds of 320 km/h (199 mph) in normal operation: originally LGVs were defined as lines permitting speeds greater than 200 km/h (124 mph), revised to 250 km/h (155 mph). Like most high-speed trains in Europe, TGVs also run on conventional tracks (French: lignes classiques), at the normal maximum speed for those lines, up to 220 km/h (137 mph). This allows them to reach secondary destinations or city centres without building new tracks all the way, reducing costs compared to the magnetic levitation train project in Japan, for example, or complete high-speed networks with a different gauge from the surrounding conventional networks, in Spain and Japan, for example. High-Speed Rail in France Track Design High-speed railway track construction in France has a few key differences from normal railway lines. The radii of curves are larger so that trains can traverse them at higher speeds without increasing the centripetal acceleration felt by passengers. The radii of LGV curves have historically been greater than 4 km (2.5 mi): new lines have minimum radii of 7 km (4.3 mi) to allow for future increases in speed. 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 quickly without greatly increasing energy consumption. The Paris-Sud-Est LGV has gradients of up to 3.5% (on the German NBS high-speed line between Cologne and Frankfurt they reach 4%). 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 (UIC 60) 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 points/switches are different from those on the lignes Classique's. Every LGV set of points incorporates a swingnose crossing (coeur à pointe mobile or 'moveable point frog'), which eliminates the gap in rail support that causes shock and vibration as wheels of a train pass over the 'frog' of conventional points. Eliminating these gaps makes the passage of a TGV over LGV switches imperceptible to passengers, reduces stresses on wheels and track, and permits much higher speeds, 160 km/h (99 mph). At junctions, such as the junction on the TGV Atlantique where the line to Le Mans diverges from the line to Tours, special points designed for higher speeds are installed which permit a diverging speed of 574 km/h (357 mph). 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 and noise pollution such as tunnel boom, which can be problematic at TGV speeds. High-Speed Rail in France Traffic Limitations LGVs are reserved primarily for TGVs. One reason for this is that line capacity is sharply reduced when trains of differing speeds are mixed, as the interval between two trains then needs to be large enough that the faster one cannot over-take the slower one between two passing loops. 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 ('surface') 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. The only freight trains that are generally permitted are 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 special design efforts were needed (a 'hunt for kilograms', chasse aux kilos) to keep the mass of the double-deck TGV Duplex trains within the 17 t limit when they were introduced in the 1990s. The steep gradients common on LGVs would limit the weight of slow freight trains. Slower trains would also mean that the maximum track cant (banking on curves) 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 currently under construction Nîmes/Montpellier branch of the LGV Mediterranée. 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 Outside France, LGV-type lines often carry non-TGV intercity traffic, often as a requirement of the initial funding commitments. The Belgian LGV from Brussels to Liège carries 200 km/h (124 mph) loco-hauled trains, with both the Dutch HSL-Zuid and British High Speed 1 planned to carry 200 and 225 km/h (124 and 140 mph) domestic intercity services respectively and 300 km/h (186 mph) international services. The Channel Tunnel is not an LGV, but it uses LGV-type TVM signalling for mixed freight, shuttle and Eurostar traffic at between 100 and 160 km/h (60 and 100 mph). The standard pathway for allocation purposes is the time taken by a Eurotunnel shuttle train (maximum speed 140 km/h (87 mph)) to traverse the tunnel. A single Eurostar running at 160 km/h (99 mph) occupies 2.67 standard paths, a second Eurostar running 3 minutes behind the first "costs" only a single additional path, so Eurostar services are often flighted 3 minutes apart between London and Lille. A freight train running at 120 km/h (75 mph) occupies 1.33 paths, at 100 km/h (62 mph) 3 paths. This illustrates the problem of mixed traffic at different speeds. Train Class Speed Paths
LGVs are all electrified at 25 kV 50 Hz AC. Catenary wires are kept at a greater mechanical tension than normal lines because the pantograph causes oscillations in the wire, and the wave must travel faster than the train to avoid producing standing waves that would cause the wires to break. This was a problem when rail speed record attempts were made in 1990, tension had to be increased further still to accommodate train speeds of over 500 km/h (311 mph). On LGVs only the rear pantograph is raised, avoiding amplification of the oscillations created by a front pantograph. The front power car is supplied by a cable along the roof of the train. Eurostar trains are long enough that oscillations are damped sufficiently between the front and rear power cars (British designers were wary of running a high-power line through passenger carriages, thus the centrally located power cars in the ill-fated Advanced Passenger Train), so the two power cars could be connected without a high voltage cable through passenger vehicles. The same applies when two TGVs run in multiple. On lignes classiques, slower maximum speeds prevent oscillation problems, and on DC lines both pantographs must be raised to draw sufficient current. High-Speed Rail in France Separation LGVs are fenced to prevent trespassing by animals and people. Level crossings are not 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. | |||||
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