Cant (road and rail): Difference between revisions
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[[Image:Track cycling 2005.jpg|thumb|Cant in a [[velodrome]]]] |
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''Note to editors: has been incorporated with [[Cant (road/rail)]]'' |
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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 flanges [[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 inches 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 inches and <math>d</math> is the [[degree of curvature]] in degrees per 30 m <math>V_{max}</math> is in mph. |
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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 ([[cant deficiency]]) in the United States is restricted to {{convert|75|mm|in|0|abbr=on}}, though {{convert|102|mm|in|1|abbr=on}} is permissible by waiver. The maximum value for European railways vary by country, some of which have curves with over {{convert|280|mm|0|in|abbr=on}} of unbalanced superelevation to permit high-speed transportation. The highest values are only for [[tilting trains]], because it would be too uncomfortable for passengers.<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> |
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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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==={{anchor|Off-camber turn}}Off-camber=== |
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An '''off-camber corner''' is described as the opposite of a [[banked turn]], or a negative-bank turn, which is lower on the outside of a turn than on the inside.<ref name=Radlauer/><ref name=Bentley/> It is a major factor in skilled vehicle control, both single-track and automotive; both engine-powered and human-powered vehicles; both on and off closed courses; and both on and off paved surfaces. |
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Off-camber corners are both feared and celebrated by skilled drivers.<ref name=Spinelli/><ref name=Strouse/> On race courses, they are one of a handful of engineering factors a course designer has at his disposal to challenge and test drivers' skills,<ref name=McMillan/> described by a training guide for prospective racers as "the hardest corners you will encounter" on the track.<ref name=Koch/> On the street, they are a feature of some of the world's most celebrated paved roads, such as [[Deals Gap]]<ref name=Weemes/><ref name=Cannon/> and [[NC 226A|"The Diamondback" (NC 226A)]] in North Carolina,<ref>{{citation|title=Top motorcycling roads: the Deep South|author=Scot J. Marburger|year=2011|publisher=Gunsmoke Engineering|url=http://www.gunsmoke.com/motorcycling/great_roads.html#Anchor-The-49575}}</ref> [[Ohio State Route 78|Route 78]] in Ohio,<ref name=Harrison/> [[Pennsylvania Route 125|Route 125]] in Pennsylvania,<ref name=Miller/> [[California State Route 33|Route 33]] in California,<ref name=Huffman/> and Betwys-e-Coed Triangle at [[Snowdonia National Park]] in Wales.<ref>{{citation|title=The World's Best Motorcycle Routes |publisher=MCE Insurance|url=http://www.mceinsurance.com/resources/worlds-best-motorcycle-routes/}}</ref> |
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To mountain bikers and motorcyclists on trails and dirt tracks, off-camber corners are also challenging, and can be either an engineered course feature, or a natural feature of single-track trails.<ref name="Dirt Rider"/><ref name="MTB Techniques"/><ref name=Geall/><ref name=Trevitt/> |
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Camber in virtual race circuits is carefully controlled by [[Racing video game|video game]] [[Simulation video game|race simulators]] to achieve the designer's desired level of difficulty.<ref name=McMillan/> |
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== See also == |
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* [[Camber angle]] |
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* [[Profilograph]] |
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* [[Tilting train]] |
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==References== |
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{{Reflist|30em|refs= |
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<ref name=Radlauer> |
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{{citation|title=Motorcyclopedia | first=Ed | last=Radlauer | publisher=Bowmar | year=1973 | ISBN=9780837208855 | page=46 | url=http://books.google.com/books?id=JZHoaESiG6YC | quote=Off camber turn: An off camber turn is the opposite of a banked turn. It's lower on the outside of a turn than on the inside.}}</ref> |
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<ref name=Bentley> |
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{{cite book|first=Ross | last=Bentley | title=Speed Secrets | page=78 | publisher=Motorbooks | year=1998 | isbn=0760305188 | url=http://books.google.com/books?id=qUUSdi976hgC&pg=PA78}}</ref> |
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<ref name=Spinelli> |
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{{citation|title=The fastest corners at Mosport are off-camber, downhill and blind|author=Mike Spinelli| date=July 26, 2013 | work=/Drive|url=http://drive.jalopnik.com/the-fastest-corners-at-mosport-are-off-camber-downhill-925417450}}</ref> |
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<ref name=Strouse> |
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{{citation|author=Frank Strouse | title=State Route 112 - Washington | work=Motorcycleroads.us | publisher=Screaming Eagle Web Solutions | url=http://www.motorcycleroads.us/roads/wa112.html | quote=Tight turns and some off-camber curves make this road a delight. }}</ref> |
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<ref name=McMillan> |
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{{citation| title=A Rational Approach To Racing Game Track Design | author=Luke McMillan | work=[[Gamasutra]] | date=September 6, 2011 | url=http://www.gamasutra.com/view/feature/6477/a_rational_approach_to_racing_game_.php}}</ref> |
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<ref name=Koch> |
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{{citation|title=Kenton Koch on Driving Technical Corners | author=Kenton Koch|year=2013 | work=Mazdaspeed Motorsports Development | publisher=Mazda North American Operations | url=http://mazdamotorsports.com/webapp/wcs/stores/servlet/DisplayRacerStoryView?uniqueId=2415&storeId=10001&catalogId=10001|quote=Off camber corners: These corners are the hardest corners you will encounter...}}</ref> |
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<ref name=Weemes> |
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{{citation|title=Deals Gap | author=D. H. Weemes | year=2007 | ISBN=9780595433209 | page=48 | url=http://books.google.com/books?id=_NeKB1HRL7QC&pg=PA48|quote=The road is alien and contains every type of turn and corner known to man. Its ridiculous make-up contains banked turns, U turns, S turns, off camber curves, blind corners, and a short straight or two thrown in for good measure.}}</ref> |
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<ref name=Cannon> |
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{{citation|journal=Super Streetbike|publisher=[[Bonnier Group]] | title=Deals Gap Revealed—Tail of the Dragon | author=Darryl Cannon |date=September 25, 2012 | url=http://www.superstreetbike.com/features/deals-gap-revealed-tail-dragon|quote=[One of] the two worst corners [is] "Guardrail cliff," a sharp off-camber left ...}}</ref> |
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<ref name=Huffman> |
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{{citation |
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| title=The 10 Best Fourth of July Road Trips: Great Places and the Great Roads To Get You There |
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| date=June 28, 2013 |
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| author=John Pearley Huffman |
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| work=[[Edmunds.com]] |
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| url=http://www.edmunds.com/car-reviews/features/the-10-best-fourth-of-july-road-trips.html |
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| quote=Route 33 has everything. It rolls across the Santa Ynez Mountains and plunges into the Cuyama Valley in relentlessly interesting ways. That includes midcorner elevation changes, off-camber hairpins, tightening-radius sweepers and straights long enough to hit terminal velocity. It's 72 miles of pure entertainment. |
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}}</ref> |
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<ref name=Harrison> |
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{{citation |
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| title=Riding Roller-Coaster Roads on History's Trail |
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| author=Greg Harrison |
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| journal=American Motorcyclist |
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| publisher=[[American Motorcyclist Association]] |
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| date=July 2001 |
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| pp=31-32 |
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| url=http://books.google.com/books?id=EvsDAAAAMBAJ&pg=PA31 |
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| quote=[It] offers all types of curves—off-camber tight stuff, sweepers and esses that make me scramble from one side of the bike to the other while my foot stabs for the right gear. |
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}}</ref> |
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<ref name=Miller> |
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{{cite book |
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| title=Motorcycle Road Trips (Vol. 14) Roads & Road Houses – Tour de Gastronomy |
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| editors =Backroad Bob, Robert H. Miller |
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| year=2010 |
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| ISBN = 9781452460512 |
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| contribution=PA125 - A Reptilian Tour on PA's Best Road |
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| author=Robert H. Miller (1997) |
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| page=4 |
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| url=http://books.google.com/books?id=A-bPVmBwU2UC&pg=PT4 |
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| quote=Changing elevation a thousand feet at a time as it snakes over six mountain passes it offers no rest from decreasing radius, off-camber, blind and switchback curves. |
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}}</ref> |
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<ref name=Geall>{{cite book|title=The Ultimate Guide to Mountain Biking|authors=Steve Geall, Robin Kitchin, Greg Minaar|page=57|publisher=Globe Pequot|year=2001|ISBN=9781585743032|url=http://books.google.com/books?id=nkbDw6wP58oC&pg=PT57}}</ref> |
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<ref name=Trevitt>{{citation|journal=[[Sport Rider]]|title=Riding skills series: Camber and Elevation—Using Both to Your Advantage|author=Andrew Trevitt|date=October 3, 2011|url=http://www.sportrider.com/sportbike-riding/riding-skills-series-camber-and-elevation}}</ref> |
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<ref name="MTB Techniques">{{citation|publisher=MTB Techniques|title=Advanced Off Camber|url=http://www.mtbtechniques.co.uk/AdvancedOffCamber.html}}</ref> |
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<ref name="Dirt Rider"> |
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{{citation|journal=Dirt Rider|title=Riding Off-Camber Corners Over A Rise With Andrew Short – Pro Secrets – Dirt Rider Magazine|date=July 21, 2009|url=http://www.dirtrider.com/features/protips/riding/141_0907_pro_secrets_off_camber_corners_andrew_short/}}</ref> |
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}} <!-- end of references--> |
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==Further reading== |
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*{{citation|journal=Road & Track| title=What's It Really Like Out There? | first=Paul | last=Van Valkenberg | volume=35 | date=October 1983 | pp=67–69 | url=http://books.google.com/books?ei=pi92VMmOEsquogTfmoHoBg&id=rR9QAAAAYAAJ | quote=course with no isolated textbook turns: Every corner is either combined with another, or banked, off-camber, rising or falling. }} |
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*{{cite book | title=Destination Highways: Washington | isbn=0968432816 | first1=Brian | last1=Bosworth | first2=Michael | last2=Sanders | publisher=Twisted Edge Publishing | location=Vancouver, B.C. | year=2003 | url=http://washington.destinationhighways.com}} — includes camber in evaluating engineering of roads, one of six numerical factors modeled to determine desirability for [[motorcycle touring]] |
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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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Revision as of 22:47, 1 December 2014
Note to editors: has been incorporated with Cant (road/rail)