View source for Level junction

{{Short description|Type of railway junction}}
{{Distinguish|Level crossing}}
{{More citations needed|date=February 2008}} 
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 | caption1  = Flat junction: trains have to wait to cross the 'diamond' at the center

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 | caption2  = A schematic diagram of a [[dual gauge]] diamond crossing

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 | caption3  = Several diamond crossings (now obsolete after removal of one track direction) in the [[Port of Mainz]], [[Germany]]

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 | caption4  = A fully assembled level junction used where the [[Union Pacific Railroad|Union Pacific]] and [[Kansas and Oklahoma Railroad|Kansas & Oklahoma]] tracks cross

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A '''level junction''' (or in the [[United Kingdom]] a '''flat crossing''') is a [[Junction (rail)|railway junction]] that has a track configuration in which merging or crossing railroad lines provide track connections with each other that require trains to cross over in front of opposing traffic [[At-grade intersection|at grade]] (i.e. on the level).

The cross-over structure is sometimes called a '''diamond junction''' or '''diamond crossing''' in reference to the diamond-shaped center. The two tracks need not necessarily be of the same [[Rail gauge|gauge]].
A diamond crossing is also used as a component of a [[double junction]], like the one illustrated on the right.

The opposite of a level junction is a [[flying junction]], where individual tracks rise or fall to pass over or under other tracks.

== Risks ==
Conflicting routes must be controlled by [[Interlocking|interlocked]] [[Railway signal|signals]] to prevent collisions.

Level junctions, particularly those of fine angles or near right angles, create [[derailment]] risks and impose speed restrictions. The former can occur as the flanges of the wheels are momentarily unsupported and unguided and can slip through the gaps in the rails, and the latter because the assembly contains elements that can break or vibrate loose.

Level junctions are considered a maintenance issue by railroad companies as the inherent gaps tend to be hard on locomotive and rolling stock wheelsets. [[Double junction#Switched diamond|Switched diamond]]s partially solve these problems, but introduce new ones.

== Examples ==
Flat crossings are particularly common in the [[United States]] where the lines of one company cross the lines of another company, and there is no particular need for the lines to be connected for through traffic.

Some examples of two tracks crossing another two tracks:
* At [[Rochelle Railroad Park]] in the [[United States]], the double track [[Union Pacific Railroad]] main line crosses the double track [[BNSF Railway]] main line forming four diamond crossings altogether at this location.
* At [[Nagpur]], [[India]]. Nagpur is where trunk railway lines running from Kolkata in the Eastern end of India to Mumbai in the Western end, and the one from Delhi in the Northern end to Chennai and other places in the southern end cross. Nagpur in fact is the geographical Centre of the Indian subcontinent. The double lines crossing from the North to the South and those from East to West form a set of four diamonds. This type is also called as "True Diamond Crossing".
* At [[Newark flat crossing]]<ref>{{cite web |url=http://maps.google.co.uk/maps?ll=53.0906,-0.8048&t=k&z=19 |title=Google Maps |website=Google Maps }}</ref> in the [[United Kingdom]], where the [[East Coast Main Line]] and [[Nottingham to Lincoln Line]] cross. This is the fastest flat-crossing in the UK, with trains travelling north-south allowed to cross the junction at 100&nbsp;mph (160&nbsp;km/h). Protection of the junction is controlled by signalling.
* Grafton, Ohio SR57 at Cleveland St

=== Local transport ===
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 | footer    = A pair of level junction interlaced turnouts at [[Chicago Transit Authority]] [[Signal tower|control tower]] 18 on the elevated [[Chicago "L"]] north and southbound [[Purple Line (Chicago Transit Authority)|Purple]] and [[Brown Line (Chicago Transit Authority)|Brown]] lines intersecting with east and westbound [[Pink Line (Chicago Transit Authority)|Pink]] and [[Green Line (Chicago Transit Authority)|Green]] lines and the looping [[Orange Line (Chicago Transit Authority)|Orange]] line above the [[Wells Street (Chicago)|Wells]] and [[Lake Street (Chicago)|Lake]] street [[intersection (road)|intersection]] in the  [[Loop (CTA)|loop]].
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Flat crossings appear in some urban passenger rail systems, which can cause delays at peak hours as a train heading in one direction may have to wait for trains heading in another direction to clear the junction before it can cross.  The junctions leading onto and off from the Loop of the [[Chicago "L"]] are examples of this problem. The [[New York City Subway]] system mostly uses [[flying junction]]s, but in a few older parts of the system, flat crossings can still cause delays. Examples include the [[142nd Street Junction]] and the [[Myrtle Avenue (BMT Jamaica Line)|Myrtle Avenue]] junction.

Level junctions are often found on [[tram]] or [[streetcar]] networks where lines cross or split. The [[MBTA]] in Boston has two of these underground on the [[Green Line (MBTA)|Green Line]], one where the [[Green Line E branch|E Line]] departs the central subway just west of [[Copley Station]], and another where the [[Green Line C branch|C Line]] and [[Green Line D branch|D Line]] split west of [[Kenmore Station]]. While the latter crossing rarely causes delays, the former is at an intersection of four lines and cars often have to wait for others to pass at peak hours. Earlier such splits in Boston (such as the disused crossing west of [[Boylston Station]]) were built as flying junctions, but the two level splits were built as level junctions mostly to save money.

=== Different gauges ===
A [[diamond crossing]] between {{Track gauge|sg|allk=on}} and {{Track gauge|1600mm|lk=on}}, [[broad gauge]] exists at [[Ararat, Victoria|Ararat]] in [[Victoria (Australia)|Victoria]], [[Australia]]{{citation needed|date=October 2014}}.

At [[Porthmadog]], in the [[United Kingdom]], there is a flat-crossing between the single track [[standard gauge]] [[Cambrian Line]] and the narrow-gauge [[Welsh Highland Railway]] ({{RailGauge|1ft11.5in|disp=or}}, also single track).<ref>Glyn Williams, [http://www.sinfin.net/railways/tourist/touristcym.html Tourist and Enthusiast Railways, Wales]. Retrieved 2008-03-21.</ref>

In [[Darby, Pennsylvania]], USA, the [[SEPTA Route 11]] line, using [[Pennsylvania trolley gauge]] of {{Track gauge|5ft 2 1⁄2 in}}, crosses [[CSX Transportation]] using standard gauge.<ref>{{cite web |url=http://ktransit.com/transit/NAmerica/useast/philadelphia/lightrail/phl-lr-rt11.htm|title=Philadelphia Transit; Streetcars;Route 11 (Kavanaugh Transit Systems) |website=KTransit.com }}</ref>

In [[South Bay, San Diego]] at the [[South Bay Salt Works]], as of 2001, survives the only crossing of narrow gauge track with standard gauge track, formerly utilized by the [[San Diego and Arizona Eastern Railway]], in the United States.<ref>{{cite web |url=http://lcweb2.loc.gov/master/pnp/habshaer/ca/ca3900/ca3901/data/ca3901data.pdf |title=Western Salt Company Works |first1=Angie |last1=Gustafson |author2=Carrie Gregory |author3=Karen J. Weitze |date=2001 |website=Historic American Landscapes Survey |publisher=Library of Congress |access-date=29 April 2015 }}</ref>

In [[Sofia]], [[Bulgaria]], there are two diamond crossings between tracks of the [[Trams in Sofia|Sofia tramway]] and a standard gauge railway line that connects Zaharna fabrika station with Zemlyane [[thermal power plant]]. One crossing is at Aleksandar Stamboliyski boulevard where the railway line crosses narrow gauge tram routes 8 and 10. The other is at Vazkresenie boulevard where it crosses tram routes 11 and 22. This second crossing is rather unique, as the tram track there is [[dual gauge]]. Route 11 uses narrow gauge while route 22 uses standard gauge. The railway line is rarely used, however. Most recently it saw use during the [[2009 Russia–Ukraine gas dispute|2009 Gas Crisis]] when Zemlyane TPP temporarily switched from burning natural gas to burning [[mazut]], which was delivered to the power plant by train. In addition, the Sofia tramway has three diamond crossings between narrow and standard gauge tram tracks.

== Drawbridge crossing ==
In [[Queensland]], [[Australia]], a number of flat crossings between [[narrow gauge railway|narrow gauge]] ({{RailGauge|610mm}}) cane tramways and main lines ({{RailGauge|1067mm}}) have been replaced by [[drawbridge]]s so that the rails of the main line are completely unbroken by gaps or weak spots: this allows the main line speeds to be raised.<ref>{{cite web |url=http://www.sa-transport.co.za/trains/sugar_cane_rail/drawbridges.html |title=Sugar Cane Railway Drawbridges and Catch-points Photos and Information |website=Sa-Transport.co.za }}</ref>

== See also ==
* [[Diamond crossing]]
* [[Double junction]]
* [[Junction (rail)]]
* [[Flying junction]]

== References ==
{{Reflist}}

== External links ==
* {{Commonscat-inline|Diamond crossings}}

{{Railway track layouts}}

[[Category:Rail junction types]]

[[ja:平面交差]]