High-speed rail
High-speed rail is a type of rail transport that operates significantly faster than traditional rail traffic, using an integrated system of specialized rolling stock and dedicated tracks. While there is no single standard that applies worldwide, new lines in excess of and existing lines in excess of are widely considered to be high-speed, with some extending the definition to include lower speeds in areas for which these speeds still represent significant improvements. The first such system began operations in Japan in 1964 and was widely known as the bullet train. High-speed trains normally operate on standard gauge tracks of continuously welded rail on grade-separated right-of-way that incorporates a large turning radius in its design.
Development of the TGV
The TGV (, high-speed train) is France's high-speed rail service. The idea of a high-speed train in France was born about twenty years before the first TGVs entered service. At that time, about 1960, a radical new concept was thought up; combining very high speeds and steep grades would allow a railway to follow the contours of existing terrain, like a gentle roller coaster. Instead of one or two percent grades which would be considered steep in normal applications, grades up to four percent would be feasible, thus allowing more flexible (and cheaper) routing of new lines. Over the next several years, this very general idea gave rise to a variety of high speed transportation concepts, which tended to move away from conventional "wheel on rail" vehicles. Indeed, the French government at the time favoured more "modern" air-cushioned or maglev trains, such as Bertin's Aérotrain; Steel wheel on rail was considered a dead-end technology. Simultaneously, SNCF (the French national railways) was trying to raise the speeds of conventional trains into the range 180 to 200 km/h (110 to 125 mph) for non-electrified sections, by using gas turbines for propulsion. Energy was reasonably cheap in those years, and gas turbines (originally designed for helicopters) were a compact and efficient way to fulfil requirements for more power. Following on the TGS prototype in 1967, SNCF introduced gas turbine propulsion with the ETG (Elément à Turbine à Gaz, or Gas Turbine Unit) turbotrains in Paris - Cherbourg service, in March 1970.