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A double junction is a railway junction where a double track railway splits into two double track lines. Usually, one line is the main line and carries traffic through the junction at normal speed, while the other track is a branch line that carries traffic through the junction at reduced speed.
A number of configurations are possible.
The simplest and oldest arrangement consists of two turnouts and a fixed Diamond crossing. Because the diamond needs to be relatively coarse, say 1 in 8, the curve radius is necessarily small, leading to a speed of perhaps 25 km/h (16 mph). This type of junction is common on street-running tramways, where speeds are quite low and junction must fit into the available road space. Because the points are close together, the entire junction can be controlled by the mechanical point rodding of a single signal box.
Signal passed at danger (SPAD) protection — A train from R to P with 12 points reverse is protected from a train from P doing a SPAD by 11 points also lying reverse. A train from P to Q is NOT protected from a train from R doing a SPAD.
The fixed diamond can be replaced with a switched diamond, which eliminates the gap in rails at the K-crossing, which allows a higher speed if the geometry is poor. However, switched diamonds are not a perfect solution to the K-crossing problem, as the switches are very coarse compared to the finer switches of a turnout, and require high maintenance. The additional ends are also awkward to control unless power operated point machines are used.
An improved junction replaces the diamond with turnouts, which can be of as fine an angle as possible, so that this junction can carry branch traffic at high speed. This configuration assumes power operation of the points, as high speed turnouts are generally not suitable for mechanical operation. The high speed turnouts may require more than one point machine each. The turnouts can have no superelevation while the curve in the branch can; therefore the radius in the turnouts must be greater than the radius of the curve in the branch.
Since the ladder type junction requires much more length, diamond type junctions can only be converted into ladder types if there is room and no bridges, tunnels, or platforms in the way.
Essentially the same as for a double junction with diamond.
Examples include Harris Park railway station, Sydney.
A single lead junction is used where traffic density is lower, and moves one of the turnouts on the main line onto the branch. This reduces the number of turnouts on the main line that are subject to wear.
Space permitting, a single lead junction may be a stage towards construction of a higher speed ladder junction. This is shown as blue dashed line on the diagram.
However, unlike in the ladder, branch trains in opposite directions can collide head-on at 32 if either one passes a signal at danger (SPAD). This has contributed to fatal accidents, e.g. in the UK at: Glasgow Bellgrove on 6 March 1989 and Newton on 21 July 1991.These risks can be reduced by trap points, ATP or TPWS.
The diamond crossing is a high wearing and undesirable component:
A right hand single lead junction cannot protect against a collision should the Q-P train overrun the signal protecting the junction, and this is not ameliorated by reverting to a double junction.
A double junction with a diamond can have its speed limit raised if the track centres are widened from say 4 m to say 12 m to allow for a fixed coarse-angled diamond crossing with fine-angled turnouts.
If the legs of the coarse crossing X are straight and flat, then this arrangement eliminates the need for switched diamonds and their inconvenient moving parts.
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Essentially the same as for a double junction with diamond.
The Channel Tunnel has at its entrances a scissors crossover implemented with two turnouts replacing the usual diamond crossing in the middle. This is only possible because of the wide track centres caused by the wide spacing of the entrances to the tunnel. The result is high speeds on the turnout routes through those turnouts and minimum wear and tear.
All the turnouts, P, Q, R, S, X1 and X2 are all the same high speed. Track centres need to be at least twice the normal track centres as if there was a hidden track in between.
All the turnouts are identical except for handedness.
Were this junction be made with a Diamond crossing in the middle, speeds through the turnout would be much reduced, and wear and tear on the diamond would be high.
At Hornsby the site is very constrained and speeds through the diamond crossing was only 8km/h, increased to 15km/h after a few changes. The site does not permit any further increase, and the restrictions dating from 1890 remain. Track centres are 12' (3.66m) throughout.
Colour coding is as follows:
A double junction can be grade separated so that there is no flat crossing, reducing conflicts and reducing congestion. Flyovers require a lot of space both lengthwise and crosswise, and cannot always be built. Flying junction example at Aynho Junction. Diving junctions such as at Chatswood are a variant. Weaver Junction is the oldest flying junction in the United Kingdom and perhaps the world. See also Aynho Junction.
Because the diamond crossing or equivalent is eliminated, one of the potential SPAD hazards is also eliminated, leaving just the merging junction hazard.
A railroad switch (AE), turnout, or [set of] points (BE) is a mechanical installation enabling railway trains to be guided from one track to another, such as at a railway junction or where a spur or siding branches off.
In railroad structures, and rail terminology, a wye or triangular junction is a triangular joining arrangement of three rail lines with a railroad switch at each corner connecting to each incoming line. A turning wye is a specific case.
A junction, in the context of rail transport, is a place at which two or more rail routes converge or diverge. This implies a physical connection between the tracks of the two routes, provided by points and signalling. Junctions are important for rail systems, their installation into a rail system can expand route capacity, and have a powerful impact upon on-time performance.
The Train Protection & Warning System (TPWS) is a train protection system used throughout the two UK passenger main-line railway networks, and in Victoria, Australia.
A derailment occurs when a vehicle such as a train runs off its rails. Although many derailments are minor, all result in temporary disruption of the proper operation of the railway system and they are potentially seriously hazardous to human health and safety. Usually, the derailment of a train can be caused by a collision with another object, an operational error, the mechanical failure of tracks, such as broken rails, or the mechanical failure of the wheels. In emergency situations, deliberate derailment with derails or catch points is sometimes used to prevent a more serious accident.
A signal passed at danger (S.P.A.D.), known in the United States and Canada as running a red light, is an event on the railway where a train passes a stop signal without authority. Where colour light signals are in use, a S.P.A.D. occurs when a train passes a red signal without authority, and where semaphore signals are used, a S.P.A.D. occurs when a train passes a signal in the 'on' position without authority.
The Colwich rail crash occurred on the evening of Friday 19 September 1986 at Colwich Junction, Staffordshire, England. It was significant in that it was a high speed collision between two packed express trains. One driver was killed, but no passengers died because of the great strength of the rolling stock involved, which included examples of Mk1, Mk2 and Mk3 coaches.
The Chiltern Main Line is an inter-urban, regional and commuter railway, part of the British railway system. It links London (Marylebone) and Birmingham, the United Kingdom's two largest cities, by a 112-mile (180 km) route via High Wycombe, Banbury, and Leamington Spa.
A double-track railway usually involves running one track in each direction, compared to a single-track railway where trains in both directions share the same track.
A passing loop or passing siding is a place on a single line railway or tramway, often located at or near a station, where trains or trams travelling in opposite directions can pass each other. Trains/trams going in the same direction can also overtake, provided that the signalling arrangement allows it. A passing loop is double-ended and connected to the main track at both ends, though a dead end siding known as a refuge siding, which is much less convenient, can be used. A similar arrangement is used on the gauntlet track of cable railways and funiculars, and in passing places on single-track roads.
Facing or trailing are railway turnouts in respect to whether they are divergent or convergent. When a train traverses a turnout in a facing direction, it may diverge onto either of the two routes. When travelled in a trailing direction, the two routes converge onto each other.
A swingnose crossing or moveable point frog is a device used at a railway turnout to eliminate the gap at the common crossing which can cause damage and noise.
Catch points and trap points are types of turnout which act as railway safety devices. Both work by guiding railway carriages and trucks from a dangerous route onto a separate, safer track. Catch points are used to derail vehicles which are out of control on steep slopes. Trap points are used to protect main railway lines from unauthorised vehicles moving onto them from sidings or branch lines. Either of these track arrangements may lead the vehicles into a sand drag or safety siding, track arrangements which are used to safely stop them after they have left the main tracks.
Rail transport – means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks consisting of steel rails installed on sleepers/ties and ballast.
The railway signalling system used across the majority of the United Kingdom rail network uses lineside signals to control the movement and speed of trains.
A level junction 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.
Australian railway signalling varies between the states of Australia as each railway was established under the different colonial governments with separate legislation. As with the notorious situation of having different gauges, there are differing signal systems. New South Wales signalling systems generally follow British precepts, however American influence has increased somewhat since the 1990s. The Victorian Railways use Speed Signalling. This can cause confusion where the systems meet. For example, in New South Wales, Green-over-Red means 'Caution', indicating the next signal is at 'Stop'.
Road signs in Thailand are standardized road signs similar to those used in other nations but with certain differences. Until the early 1980s, Thailand closely followed US, Australian, and Japanese practices in road sign design, with diamond-shaped warning signs and circular restrictive signs to regulate traffic. Signs usually use the FHWA Series fonts typeface also used in the United States.
The first French high-speed rail line opened in 1981, between Paris's and Lyon's suburbs. It was at that time the only high-speed rail line in Europe. As of July 2017, the French high-speed rail network comprises 2,647 km of Lignes à grande vitesse (LGV), and 670 km are under construction.
A flange-bearing frog, often abbreviated FBF, is a type of frog in which the flange of the wheel on a railway vehicle supports the weight of the vehicle. In conventional practice, the tread of the wheel rests on the head of the rail and bears the weight of the vehicle, while the flange is used to keep the vehicle in the gauge of the track. Modern flange-bearing frogs for use in freight railroad applications are a relatively recent development as a means to reduce maintenance costs associated with turnouts and diamonds, where rails must cross one another.