A level junction (or in the United Kingdom a flat crossing) is a 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 (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 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.
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An Introduction to Switches & Crossings - Network Rail engineering education (12 of 15)
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Transcription
[train passing] ♪ background music ♪ (Narrator) Switches and crossings play an essential role in connecting the rail network. We use them to guide trains from one track to another and to enable lines to cross paths. Put simply, they're the junctions that allow us to create a multi-lined, multi-routed rail network. At Network Rail we own over 20,000 switch and crossing units. They come in many different shapes and sizes and all are made to measure for their specific location. To understand how switches and crossings work, we've first got to look at the wheel-rail interaction. Train wheels move along the rails guided only by the pound coin sized area of wheel that sits on the rail head. The wheel rim or flange doesn't normally touch the rail. Flanges are only a last resort, to prevent the wheels becoming derailed. A switch can guide a wheel in one of two directions. A crossing creates a gap in the rail for the flange to pass through. This is a switch. Also known as a point. It's the moving part of the switch and crossing layout and is made up of two long blades which can move across to guide the train one way or another. This is the switch rail. And this is called the toe. This is called the stock rail. It's a non-moving part of the switch. The two switch blades are fixed to each other by a stretcher bar to ensure that when one is against its stock rail the other is fully clear and provide room for the wheel flange to pass through cleanly. This is a crossing. It's the non-moving part of the switch and crossing layout that allows a train to pass in either direction once the switch has been set. This is the nose of the crossing. Either side of the crossing area, wing and check rails are provided to assist the guidance of the wheel sets through the crossing. Crossings can be either fabricated, made up of two machined rails joined together, or they can be cast as a single unit. Modern crossings are now cast from manganese steel which is an advanced alloy that gets harder with use. This is an important property, as the nose of the crossing can take high impact loads as train wheels pass through. (Lawrence) My name's Lawrence Wilton, and I'm a graduate engineer working for Network Rail. I'm here today to teach you about switches and crossings. The most simple form of S and C is the turn-out. This is a left-hand turn-out. As you can see, it diverges from the main route in a leftward direction. This is how it works. In normal mode, the left hand wheel rolls along the switch rail and there's flange way clearance for the right wheel to continue along the stock rail. The inside surface of the right flange is kept on course by the track rail. This restrains the wheel set and ensures it is directed along the correct route. Meanwhile, the left wheel transfers contact between the different parts of the crossing. That's where there's a high impact load. In the reverse the right wheel rolls over the switch rail and follows its geometry. The inside surface of the left flange is guided by the check, forcing it to follow the stock rail on the new route and the right hand wheel makes a crossing, again, impacting a load on the crossing nose. (Narrator) There are many different types of switch and crossing on the network. They include turn-outs, diamonds, cross-overs, and slip-diamonds. The type we use is determined by a number of factors including the number of lines involved, frequency of use and running line speed. Trains travelling at high speeds need long switches and crossings. At low speed, such as in stations, trains can make tighter turns. Train movements across the network are set and controlled by signallers who use switches to set routes for trains. Switches can be propelled by various devices. One of the simplest forms is a ground frame set-up. A series of rods and cams attached to levers in signal boxes. These are now largely being replaced by remotely operated hydraulic and electro-mechanical devices. (Lawrence) Seen by rail-sides all across the country, this is an HW2000 points machine. This is electro-mechanical. What we have here is your drive motor. To check that motor has done its job, over here we have an interlocking and detection system. Detection tells us when the points have completed their travel and locked. Locking holds the points in this state, so they cannot be physically moved. So when a train runs over the top, it remains in position. Facing point locks are one of the most important safety features on the S and C layout. They ensure that the points cannot be moved when set. This is important because failure to lock the switches could cause a derailment. (Narrator) As engineers, we face an ongoing challenge to maintain and improve our switch and crossing assets. Trains can create large impact and lateral forces as they change course. And these forces can cause wear and deformation. Switches and crossings therefore have a limited lifespan before we need to replace them. Less than 5% of track miles are made up of switches and crossings, but over 17% of our maintenance budget is spent on them. We'll continue to research and develop new inspection techniques and material usage to increase their performance. (Lawrence) It's all about creating a network that's safe, reliable and efficient. It's what we do.
Risks
Conflicting routes must be controlled by interlocked 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. Switched diamonds 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.
Three 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[1] 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 mph (160 km/h). Protection of the junction is controlled by signalling.
- Grafton, Ohio SR57 at Cleveland St
Local transport
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 junctions, 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 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, one where the E Line departs the central subway just west of Copley Station, and another where the C Line and 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 1,435 mm (4 ft 8+1⁄2 in) standard gauge and 1,600 mm (5 ft 3 in), broad gauge exists at Ararat in Victoria, Australia[citation needed].
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 (1 ft 11+1⁄2 in or 597 mm, also single track).[2]
In Darby, Pennsylvania, USA, the SEPTA Route 11 line, using Pennsylvania trolley gauge of 5 ft 2+1⁄2 in (1,588 mm), crosses CSX Transportation using standard gauge.[3]
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.[4]
In Sofia, Bulgaria, there are two diamond crossings between tracks of the 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 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 (610 mm (2 ft)) cane tramways and main lines (1,067 mm (3 ft 6 in)) have been replaced by drawbridges 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.[5]
See also
References
- ^ "Google Maps". Google Maps.
- ^ Glyn Williams, Tourist and Enthusiast Railways, Wales. Retrieved 2008-03-21.
- ^ "Philadelphia Transit; Streetcars;Route 11 (Kavanaugh Transit Systems)". ktransit.com.
- ^ Angie Gustafson; Carrie Gregory; Karen J. Weitze (2001). "Western Salt Company Works" (PDF). Historic American Landscapes Survey. Library of Congress. Retrieved 29 April 2015.
- ^ "Sugar Cane Railway Drawbridges and Catch-points Photos and Information". www.sa-transport.co.za.
External links
Media related to Diamond crossings at Wikimedia Commons
This page was last edited on 28 October 2023, at 19:44