Lignes à Grande Vitesse

The first French high-speed rail line opened in 1981, between Paris's and Lyon's suburbs. It was at that time the only high-speed rail line in Europe. As of December 2014, the French high-speed rail network comprises 2,037 km of Lignes à grande vitesse (LGV), and 670 km are under construction.

In 1976, the government agreed to fund the first line. The LGV opened to the public between Paris and Lyon on 27 September 1981.

Other LGVs are:

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

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 solutions in Japan and China, for example, or complete high-speed networks with a different gauge from the surrounding conventional networks, in Spain and Japan, for example.

TGV track construction 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 grades 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.

...
Wikipedia