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| [[Image:Track cycling 2005.jpg|thumb|Cant in a [[velodrome]]]]
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| The '''cant''' of a [[railway]] track (also referred to as '''superelevation''') or a [[road]] (sometimes referred to as [[cross slope]] or [[camber angle|camber]]) is the difference in elevation (height) between the two edges. This is normally done where the railway or road is curved; raising the outer rail or the outer edge of the road providing a [[banked turn]], thus allowing vehicles to maneuver through the curve at higher speeds than would otherwise be possible if the surface was flat or level.
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| == Rail ==
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| {{further2|[[Rail tracks]]}}
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| {{See also|Track class (United States)|Cant deficiency}}
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| [[Image:Überhöhung NBS.jpg|thumb|The ''cant'' in a curve of the [[Nuremberg-Munich high-speed rail line|Nuremberg–Ingolstadt line]]]]
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| [[Image:Rail track lubricator.jpg|thumb|right|Track lubrication on a reverse curve in an area prone to movement due to wet beds]]
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| On railways, cant helps a train steer around a curve, keeping the wheel flanges from touching the rails, minimising friction and wear.
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| The main functions of cant are to:
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| * Better distribute load across both rails
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| * Reduce rail- and wheel-wear
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| * Neutralise the effect of lateral forces
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| * Improve passenger comfort
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| [[File:Railway superelevation at Dunbar, July 2012.jpg|thumb|right|Railway superelevation at work.]]
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| The necessary cant in a curve depends on the expected speed of the trains and the [[radius]]. However, it may be necessary to select a compromise value at design time, for example if slow-moving trains may occasionally use tracks intended for [[high-speed trains]].
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| Generally the aim is for trains to run without [[flange]] contact, which also depends on the [[tyre profile]] of the wheels. Allowance has to be made for the different speeds of trains. Slower trains will tend to make flange contact with the inner rail on curves, while faster trains will tend to ride outwards and make contact with the outer rail. Either contact causes [[wear and tear]] and may lead to derailment. Many high-speed lines do not permit slower freight trains, particularly with heavier [[axle load]]s. In some cases, the impact is reduced by the use of flange [[lubrication]].
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| Ideally, the track should have sleepers ([[railroad tie]]s) at a closer spacing and a greater depth of [[Track ballast|ballast]] to accommodate the increased forces exerted in the curve.
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| At the ends of a curve, the amount of cant cannot change from zero to its maximum immediately. It must change ([[wikt:ramp|ramp]]) gradually in a [[track transition curve]]. The length of the transition depends on the maximum allowable speed—the higher the speed, the greater length is required.
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| In the United States, maximum speed is subject to specific rules. The maximum speed of a train on curved track for a given cant deficiency or unbalanced superelevation is determined by the following formula:<ref>{{cite web|url=http://www.highspeed-rail.org/Documents/305%20PRIIA%20Tilt%20presentation.pdf|title=Cant Deficiency, Curve Speeds and Tilt|last=Marquis|first=Brian |accessdate=2011-10-14}}</ref>
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| :<math>V_{max}=\sqrt{\frac{E_a + E_u}{0.0007d}}</math>
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| where <math>E_a</math> is the height in cm that the outside rail is "superelevated" above the inside rail on a curve, <math>E_u</math> is the unbalanced superelevation or cant deficiency in cm and <math>d</math> is the [[degree of curvature]] in degrees per 30 m <math>V_{max}</math> is in km/h.
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| For the United States standard maximum unbalanced superelevation of {{convert|75|mm|in|0|abbr=on}}, the formula is:
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| :<math>V_{max}=\sqrt{\frac{E_a + 3}{0.0007d}}</math>
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| The maximum value of cant (the height of the outer rail above the inner rail) for a [[standard gauge]] railway is about {{convert|150|mm|in|0|abbr=on}}.{{Citation needed|date=February 2007}} For high-speed railways in Europe, maximum cant is {{convert|180|mm|in|0|abbr=on}} (when slow freight trains are not allowed).<ref>2002/732/EC. *, Commission Decision of 30 May 2002 concerning the Technical Specification for Interoperability</ref> | |
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| Track unbalanced superelevation in the United States is restricted to {{convert|75|mm|in|0|abbr=on}}, though {{convert|10|mm|in|1|abbr=on}} is permissible by waiver. There is no general maximum set for European railways, some of which have curves with over {{convert|280|mm|0|in|abbr=on}} of unbalanced superelevation to permit high-speed transportation.<ref>{{cite web|url=http://Zierke.com/shasta_route/pages/05curve-curve.html|title=Comparison of upgrades needs to recognize the difference in curve speeds|last=Zierke|first=Hans-Joachim |accessdate=2008-04-10}}</ref> There are country-specific regulations that may apply, though.
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| === Examples ===
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| In Australia, [[Australian Rail Track Corporation|ARTC]] is increasing speed around curves sharper than an {{convert|800|m|ft|0|adj=on}} radius by replacing wooden sleepers with concrete ones so that the cant can be increased.<ref>{{cite journal|title=North South – strategy for growth Craven AU$421.6 million Investment for Sydney Brisbane Corridor|journal=Links|date=August 2005 |issue=11|url=http://web.archive.org/web/20090929145144/http://www.artc.com.au/library/Links%2011.pdf|accessdate=22 November 2012|publisher=Australian Rail Track Corporation Ltd.|quote=Concrete re-sleepering of all curves of less than an 810-metre radius, using some 220,000 sleepers to increase cant deficiency and super-elevation, will be undertaken allowing for increased train speeds and further reducing transit times.}}</ref>
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| === Rail cant ===
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| The rails themselves are now usually canted inwards by about 10 to 5 per cent.
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| In 1925 about 15 of 36 major railways had adopted this practice.<ref>{{cite news |url=http://nla.gov.au/nla.news-article25099255 |title="KNOCK-KNEED" RAILS. |newspaper=[[The Queenslander|The Queenslander (Brisbane, Qld. : 1866 - 1939)]] |location=Brisbane, Qld. |date=7 February 1925 |accessdate=20 November 2011 |page=9 |publisher=National Library of Australia}}</ref>
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| == Roads ==
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| ''See also [[Geometric design of roads]]''
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| In [[civil engineering]], cant is often referred to as [[cross slope]] or camber. It helps rainwater drain from the road surface. Along straight or gently curved sections, the middle of the road is normally higher than the edges. This is called "normal crown" and helps shed rainwater off the sides of the road. During road works that involve lengths of temporary carriageway, the slope may be the opposite to normal – i.e. with the outer edge higher – which causes vehicles to lean towards oncoming traffic: in the UK this is indicated on warning signs as 'adverse camber'.
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| On more severe bends, the outside edge of the curve is raised, or '''superelevated,''' to help vehicles around the curve. The amount of superelevation increases with its [[design speed]] and with curve sharpness.
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| == See also ==
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| * [[Banked turn]]
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| * [[Camber angle]]
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| * [[Cant deficiency]]
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| * [[Profilograph]]
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| * [[Tilting train]]
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| == References ==
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| {{reflist}}
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| {{Rail tracks}}
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| {{Railway track layouts}}
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| {{DEFAULTSORT:Cant (Road Rail)}}
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| [[Category:Track geometry]]
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| [[Category:Road infrastructure]]
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