HSR is still a grounded, guided and low grip transport system: it could be considered to be a railway subsystem. The most important change comes from the speed. As travel times had to be reduced for commercial purposes, speed emerged as the main factor. HSR means a jump in commercial speed and this is why UIC considers a commercial speed of 250 km/h to be the principal criterion for the definition of HSR.

However, a secondary criterion is admitted on average distances without air competition, where it may not be relevant to run at 250 km/h, since a lower speed of 230 or 220 km/h or at least above 200 km/h (since under this speed conventional trains can do) is enough to catch as many market shares as a collective mode of transport can do. This also applies in very long tunnels whose construction cost depends on the diameter linked to the square of the speed, at least. For such speeds above 200 km/h, the infrastructure can be categorized in “High-Speed” if the system in operations, complies with:

• track equipment,
• rolling stock (generalisation of trainsets),
• signalling systems (abandonment of trackside signals),
• operations (long-range control centres),
• the geographical or temporal separation of freight and passenger traffics,
• and more globaly with the standards for High-Speed.