- Railway slide fence
Part of a railway signaling system, a slide fence is a fence whose purpose is to prevent trains from being derailed by rock slides in mountainous areas where rock slides may occur without warning. The fence is designed to be displaced by a rock slide, causing the signaling system to display a stop aspect on nearby signals. [ [http://broadway.pennsyrr.com/Rail/Signal/glossary.html Railway Signalling and Operations, Glossary of Signalling Terms] ] As an alternative, a structural fence is designed to physically stop falling rocks from reaching the tracks.
The mechanical slide fence consists of a series of tensioned wires strung about 10 inches (25 cm) apart on poles. When a rock slide occurs, the rock breaks one or more of the wires. When a wire breaks, heavy weights attached to either end will fall. This mechanically triggers the protecting signals to the 'danger' position.
There are two types of electrical slide fence in operation. [This is described in section 5.1.12 of the AREMA C&S Manual.]
One type of electrical slide fence consists of a series of parallel conductive wires strung about 8 inches (20 cm) apart on poles that create a fence parallel to the rails.
This creates an electrical circuit that is monitored by signaling equipment. In normal operation, the
electric currentin the fence wires causes a relayto energize, indicating that the fence is intact. When a rock slide occurs, the rock breaks one or more of the wires, interrupting the current. This causes the relay to become de-energized, indicating that a rock slide has occurred. A contact of the relay is typically used to prevent the approaching signal from displaying a proceed aspect if the fence has been broken. [ [http://www.arema.org/ The American Railway Engineering and Maintenance of Way Association] ] Restoring normal operation requires splicing the broken fence wires back together.
Another type of slide fence is similar except that the wires do not have to break and is easier to maintain and reset. The slide fence consists of a series of fence sections, as shown in the SLIDE FENCE DETAIL drawing, which shows a typical installation. Each fence section is held in place by strong springs. At each end of a fence section is an electro-mechanical plug. The plugs maintain a complete electrical circuit that is monitored by signaling equipment. In normal operation, the current through the plugs causes a
relayto energize, indicating that the fence is in place. When a rock slide occurs, the fence moves laterally, causing the plug to be removed, breaking the circuit. This causes the relay to become de-energized, indicating that a rock slide has occurred. A contact of the relay is typically used to prevent the approaching signal from displaying a proceed aspect if the fence has been broken. [ [http://www.arema.org/ The American Railway Engineering and Maintenance of Way Association] ] Restoring normal operation requires re-inserting the plugs that were dislodged by the slide.
The structural fence is a physical barrier designed to stop falling rocks from reaching the tracks. Several construction methods are used, including: steel I-beams, wooden barriers, galvanized fencing, and netting directly against the rock.
A slide fence is typically found in mountainous areas in a rock cut area, where rocks may fall on the track and present a danger to passing trains. The length of the fence may range from 100 feet (30 meters) to several miles (kilometers), depending on the length of the rock cut and the area being protected. The slide fence is usually located on the uphill side of the track in the slide area.
Consequences of slide fence activation
to proceed slowly, watching for a dangerous rock slide. If the train is able to successfully pass through the slide area (that is, there is no danger), it may then be allowed to proceed normally.
In North America slide fences are typically connected in such a way as to shunt the
track circuitwhen activated. This causes signals on either side of the slide fence to display a restricting indication, requiring trains to travel at a speed enabling them to stop within one half the range of vision. On lines formerly operated by the Pennsylvania Railroadsignals connected to a slide detector have an 'SP' placard, reminding engineers to watch for slides when governed by a restrictive speed signal.
Once the slide fence has been activated (even if in error), all trains are affected until the slide fence is repaired by maintenance personnel. This may result in several hours of delay in train service.
Several alternative technologies have been tried to solve the rock slide problem, including:
*Acoustic sensing [ [http://www.patentstorm.us/patents/6216985-description.html US Patent 6216985 Railway hazard acoustic sensing, locating, and alarm system] ]
*Electromagnetic sensing [ [http://www.tc.gc.ca/TDC/publication/pdf/13900/13928e.pdf/ Railway Rockfall Electromagnetic Field Disturbance Sensing System Development and Test Results] ]
*Seismic sensing [ [http://www.tc.gc.ca/tdc/projects/rail/h/5656.htm/ Transport Canada Seismic Rail line rockfall monitoring] ] [ [http://www.weir-jones.com/images/NEW_PDF/srfds-e.pdf Seismic Rock Fall Detection System (SRFDS)] ] [ [http://www.alstomsignalingsolutions.com/OurProducts/NewProducts/MRMS/ Microseismic Rock Monitoring System (MRMS)] ]
*Visual sensing, using cameras
Pass of Brander stone signals
Wikimedia Foundation. 2010.
Look at other dictionaries:
Railway signalling — Not to be confused with Railway signal. A gantry of British semaphore signals seen from the cab of a steam locomotive Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being… … Wikipedia
Railway signal — Not to be confused with Railway signalling. A signal is a mechanical or electrical device erected beside a railway line to pass information relating to the state of the line ahead to train/engine drivers. The driver interprets the signal s… … Wikipedia
Token (railway signalling) — A token being offered by a signalman on the Keighley and Worth Valley Railway … Wikipedia
Norwegian railway signalling — The signalling system used on the rail transport in Norway is regulated by the Regulations of December 4, 2001 no. 1336 about signals and signs on the state s railway network and connected private tracks. The first signalling system on the… … Wikipedia
North American railway signaling — For the actual physical signals, see North American railroad signals. Standards for North American railway signaling in the United States are issued by the Association of American Railroads (AAR), which is a trade association of the railroads of… … Wikipedia
Application of railway signals — Semaphore stop signals protecting the convergence of two tracks into one The application of railway signals on a rail layout is determined by various factors, principally the location of points of potential conflict, as well as the speed and… … Wikipedia
Dutch railway signalling — The current Dutch railway signalling system operated by ProRail has been in effect since 1954 on the Dutch Railways network It was designed to be one of the simplest in Europe and is integrated to the ATB, the system of cab signalling widespread… … Wikipedia
Pass of Brander stone signals — The Pass of Brander stone signals are a series of railway signals situated in the Pass of Brander, between Loch Awe and Taynuilt stations on the Oban branch of the West Highland Line in Scotland. They are part of a warning system that advises… … Wikipedia
Level crossing — This article is about at grade intersections between railway and road. For where two rail lines cross, see level junction. For a type of nuclear receptor (RXR), see Retinoid X receptor. A level crossing at Chertsey, England, as the barriers rise … Wikipedia
North American railroad signals — Main article: North American railway signaling Baltimore and Ohio Railroad Color Position Light bracket masts at Magnolia, West Virginia North American railroad signals generally fall into the category of multi headed electrically lit units… … Wikipedia