High-speed rail
Technologies
### Technologies

[thumb\|High\-speed line on a viaduct to avoid ramp and road\-crossing, with a [British Rail Class 373](/wiki/British_Rail_Class_373 "British Rail Class 373") from [Eurostar](/wiki/Eurostar "Eurostar") in old livery crossing it.](/wiki/File:Viaduc_de_la_Haute-Colme_01_09.jpg "Viaduc de la Haute-Colme 01 09.jpg")

[thumb\|A German high\-speed line, with [ballastless track](/wiki/Ballastless_track "Ballastless track")](/wiki/File:Steigung_NIM.jpg "Steigung NIM.jpg")

[Continuous welded rail](/wiki/Continuous_welded_rail "Continuous welded rail") is generally used to reduce track vibrations and misalignment. Almost all high\-speed lines are electrically driven via [overhead lines](/wiki/Overhead_line "Overhead line"), have [in\-cab signalling](/wiki/In-cab_signalling "In-cab signalling"), and use advanced switches using very low entry and [frog](/wiki/Switch_frog "Switch frog") angles. HSR tracks may also be designed to reduce vibrations originating from high speed rail use.

#### Road\-rail parallel layout

[thumb\|A German high\-speed line being built along a highway](/wiki/File:NIM_Baustelle2001_Leidorf_Koeschinger_Forst.jpg "NIM Baustelle2001 Leidorf Koeschinger Forst.jpg")

The road\-rail parallel layout uses land beside highways for railway lines. Examples include Paris/Lyon and [Köln–Frankfurt](/wiki/K%C3%B6ln%E2%80%93Frankfurt_high-speed_rail_line "Köln–Frankfurt high-speed rail line") in which 15% and 70% of the track runs beside highways, respectively. There are [synergies](/wiki/Synergies "Synergies") to be achieved from such a setup as noise mitigation measures for the road benefit the railway and vice versa and furthermore less land must be taken through [expropriation](/wiki/Expropriation "Expropriation") as land may have already been acquired for the construction of the other infrastructure. In addition to that, habitats of local wildlife are disrupted only once (by the combined rail/road right of way) instead of at multiple points. However, downsides include the fact that roads usually allow steeper grades and sharper turns than high\-speed rail lines and thus co\-locating them may not always be suitable. Moreover, both roads and railways often make use of narrow river valleys or mountain passes which do not allow a lot of infrastructure to be sited next to each other.

#### Track sharing

In China, high\-speed lines at speeds between  may carry freight or passengers, while lines operating at speeds over  are used only by passenger CRH/CR trains.

In the United Kingdom, [HS1](/wiki/High_Speed_1 "High Speed 1") is also used by regional trains run by [Southeastern](/wiki/Southeastern_%28train_operating_company%29 "Southeastern (train operating company)") at speeds of up to , and occasionally freight trains that run to central Europe.

In Germany, some lines are shared with Inter\-City and regional trains at day and freight trains at night.

In France, some lines are shared with regional trains that travel at , for example [TER Nantes\-Laval](/wiki/TER_Pays_de_la_Loire "TER Pays de la Loire").

Mixing trains of vastly different speeds and/or stopping patterns on the same tracks drastically reduces capacity, so usually a temporal separation (e.g. freight trains use the high\-speed line only at night when no or only a few passenger trains operate) is employed or the slower train has to wait at a station or [passing siding](/wiki/Passing_siding "Passing siding") for the faster train to overtake \- even if the faster train is delayed, thus delaying the slower train, too.


Is it possible to build high-speed lines that do not use continuous welded rail?