Editing Channel Tunnel (section)

=== Railway design ===
[[File:ETunnelhoch.jpg|thumb|upright|Interior of the [[Eurotunnel Shuttle]], used to carry motor vehicles through the Channel Tunnel. These are the largest railway wagons in the world.<ref name="Anderson Story p xvi-xvii"/> ]]

====Loading gauge====

The [[loading gauge]] height is {{convert|5.75|m|ftin|abbr=on}}.<ref>{{cite web |url= https://intra.kth.se/polopoly_fs/1.273361.1397150299!/Menu/general/column-content/attachment/Fran-Scan%20(G2%20PC%20450)%20-%20A%20Hi-Cube%20Intermodal%20Corridor%20to%20Link%20Britain,%20France%20and%20Scandinavia%20-%20KTH%20Boysen%202011-11-30%20rev%201930.pdf |title= Fran-Scan (G2, P/C 450) – A Hi-Cube Intermodal Corridor to Link the UK, France and Scandinavia |last= Boysen |first= Hans |year= 2011 |department= Department of Transport Science Royal Institute of Technology |publisher= KTH Railway Group, Center for research and education in railway technology |page= 16 |access-date= 8 February 2019 |archive-url= https://web.archive.org/web/20190209124034/https://intra.kth.se/polopoly_fs/1.273361.1397150299!/Menu/general/column-content/attachment/Fran-Scan%20(G2%20PC%20450)%20-%20A%20Hi-Cube%20Intermodal%20Corridor%20to%20Link%20Britain,%20France%20and%20Scandinavia%20-%20KTH%20Boysen%202011-11-30%20rev%201930.pdf |archive-date= 9 February 2019 |url-status= dead }}</ref>

==== Communications ====
There are three communication systems:<ref name="Kirkland pp.129–132">Kirkland pp. 129–132</ref>
* Concession radio – for the tunnel operator's personnel and vehicles within the concession area (terminals, tunnels, coastal shafts)
* Track-to-train radio – secure speech and data between trains and the railway control centre
* Shuttle internal radio – communication among shuttle crew, and to passengers over car radios

==== Power supply ====
Power is delivered to the locomotives via an [[overhead line]] at [[25 kV AC railway electrification|{{nowrap|25 kV 50 Hz}}]]<ref name="Kirkland pp.134–148">Kirkland pp. 134–148</ref><ref name="wiki_railelectric">Article: Railway electric traction 9 August 2009</ref> with a normal overhead clearance of {{cvt|6.03|m|ftin|frac=2}}.<ref>{{cite web |url= https://www.getlinkgroup.com/content/uploads/2019/09/Eurotunnel-network-statement-2020.pdf#page=12 |title= Eurotunnel Fixed Link Usage Annual Statement – 2020 Working Timetable – |year= 2018 |page= 12 |access-date= 3 May 2021 |archive-url= https://web.archive.org/web/20210504060210/https://www.getlinkgroup.com/content/uploads/2019/09/Eurotunnel-network-statement-2020.pdf#page=12 |archive-date= 4 May 2021 |url-status= dead }}</ref> All tunnel services run on electricity, shared equally from English and French sources. There are two substations fed at 400 kV at each terminal, but in an emergency, the tunnel's lighting (about 20,000 light fittings) and the plant can be powered solely from either England or France.{{sfn|Foreign & Commonwealth Office|1994|p=9}}

The traditional railway south of London uses a 750&nbsp;V&nbsp;DC [[third rail]] to deliver electricity, but since the opening of [[High Speed 1]] there is no longer any need for tunnel trains to use it. High Speed 1, the tunnel and the [[LGV Nord]] all have power provided via overhead catenary at 25&nbsp;kV&nbsp;50&nbsp;Hz AC. The railways on "classic" lines in Belgium are also electrified by overhead wires, but at 3,000&nbsp;V&nbsp;DC.<ref name="wiki_railelectric"/>

==== Signalling ====
A cab signalling system gives information directly to train drivers on a display. There is a [[train protection system]] that stops the train if the speed exceeds that indicated on the in-cab display. [[Transmission Voie-Machine|TVM430]], as used on [[LGV Nord]] and [[High Speed 1]], is used in the tunnel.<ref name="Kirkland pp.149–155">Kirkland pp. 149–155</ref> The TVM signalling is interconnected with the signalling on the high-speed lines on either side, allowing trains to enter and exit the tunnel system without stopping. The maximum speed is {{Cvt|160|km/h}}.<ref name="wiki_de-eurotunnel">Article-de: Eurotunnel#Betrieb 9 August 2009</ref>

Signalling in the tunnel is coordinated from a control centre at the Folkestone terminal. A backup facility at the Calais terminal is staffed at all times and can take over all operations in the event of a breakdown or emergency.

==== Track system ====
Conventional ballasted tunnel track was ruled out owing to the difficulty of maintenance and lack of stability and precision. The Sonneville International Corporation's track system was chosen because it was reliable and also cost-effective. The type of track used is known as Low Vibration Track (LVT), which is held in place by gravity and friction. Reinforced concrete blocks of {{Convert|100|kg|abbr=on}} support the rails every {{convert|60|cm||1|abbr=on}} and are held by {{convert|12|mm||2|abbr=on}} thick closed-cell polymer foam pads placed at the bottom of rubber boots. The latter separates the blocks' mass movements from the concrete. The track provides extra overhead clearance for larger trains.<ref name="bonnett782">Bonnett 2005, p. 78</ref> UIC60 (60&nbsp;kg/m) rails of 900A grade rest on {{convert|6|mm|4=2|abbr=on}} rail pads, which fit the RN/Sonneville bolted dual leaf-springs. The rails, LVT-blocks and their boots with pads were assembled outside the tunnel, in a fully automated process developed by the LVT inventor, Roger Sonneville. About 334,000 Sonneville blocks were made on the Sangatte site.

Maintenance activities are less than projected. The rails had initially been ground on a yearly basis or after approximately 100MGT of traffic. Maintenance is facilitated by the existence of two tunnel junctions or crossover facilities, allowing for two-way operation in each of the six tunnel segments, and providing safe access for maintenance of one isolated tunnel segment at a time. The two crossovers are the largest artificial undersea caverns ever built, at {{cvt|150|m}} long, {{cvt|10|m}} high and {{cvt|18|m}} wide. The English crossover is {{convert|8|km||abbr=in}} from Shakespeare Cliff, and the French crossover is {{convert|12|km||abbr=in}} from Sangatte.{{sfn|Foreign & Commonwealth Office|1994|p=14}}

==== Ventilation, cooling and drainage ====
The ventilation system maintains greater air pressure in the service tunnel than in the rail tunnels, so that in the event of a fire, smoke does not enter the service tunnel from the rail tunnels. There is a normal ventilating system and a supplementary system. Twin fans are mounted in vertical shafts where digging for the tunnel began, on both sides of the channel: two in [[Sangatte]], France, and two more at [[Shakespeare Cliff Halt railway station|Shakespeare Cliff]], UK. The normal ventilating system is connected direct to the service tunnel and provides fresh air through the cross- passages into the running tunnels, where it is dispersed by the piston effect of the train and shuttle movements. Only one fan on each side is ever running, the second being available as a backup. The supplementary ventilating system is a separate emergency system and can be used to control smoke or supply emergency air within the tunnels. On both systems, the fans are normally run on supply mode, pulling in air from the outside, but they can also be used in extraction mode to remove smoke or fumes from the tunnels.<ref>{{Cite web |last=Dodge |first=Terence M. |title=Ventilating the English Channel Tunnel |url=https://www.aivc.org/sites/default/files/airbase_7421.pdf }}</ref>

Two cooling water pipes in each rail tunnel circulate chilled water to remove heat generated by the rail traffic. Pumping stations remove water in the tunnels from rain, seepage, and so on.{{sfn|Foreign & Commonwealth Office|1994|p=8}}

During the design stage of the tunnel, engineers found that its aerodynamic properties and the heat generated by high-speed trains as they passed through it would raise the temperature inside the tunnel to {{convert|50|C|F}}.<ref name="CoolingPost">{{Cite news|title=HFO chillers to cool the Channel Tunnel|date=14 September 2016|work=Cooling Post|url=https://www.coolingpost.com/world-news/hfo-chillers-to-cool-the-channel-tunnel/|accessdate=12 June 2016}}</ref> As well as making the trains "unbearably warm" for passengers, this also presented a risk of equipment failure and track distortion.<ref name=CoolingPost/> To cool the tunnel to below {{convert|35|C|F}}, engineers installed {{convert|480|km|mi|abbr=in}} of {{convert|61|cm|in|1|abbr=on}} diameter cooling pipes carrying {{convert|84|e6l|e6impgal|abbr=off}} of water. The network—Europe's largest cooling system—was supplied by eight [[York International|York Titan]] chillers running on [[Chlorodifluoromethane|R22]], a [[hydrochlorofluorocarbon]] (HCFC) refrigerant gas.<ref name=CoolingPost/><ref name="CoolingPost2">{{Cite news|title=Tunnel vision proves R1233zd efficiency|date=1 June 2018|work=Cooling Post|accessdate=12 June 2018|url=https://www.coolingpost.com/features/tunnel-vision-proves-r1233zd-efficiency/}}</ref>

Due to R22's [[ozone depletion potential]] and high [[global warming potential]], its use is being phased out in developed countries. Since 1 January 2015, it has been illegal in Europe to use HCFCs to service air-conditioning equipment; broken equipment that used HCFCs must be replaced with equipment that does not use it. In 2016, [[Trane]] was selected to provide replacement chillers for the tunnel's cooling network.<ref name=CoolingPost/> The York chillers were decommissioned and four "next generation" Trane Series E CenTraVac large-capacity (2,600&nbsp;kW to 14,000&nbsp;kW) chillers were installed—two in Sangatte, France, and two at Shakespeare Cliff, UK. The energy-efficient chillers, using [[Honeywell]]'s non-flammable, ultra-low GWP [[1-Chloro-3,3,3-trifluoropropene|R1233zd(E)]] refrigerant, maintain temperatures at {{convert|25|C|F}}, and in their first year of operation generated savings of 4.8{{nbsp}}[[GWh]]—approximately 33%, equating to €500,000 ($585,000)—for tunnel operator [[Getlink]].<ref name=CoolingPost2/>