Turnout and Crossings

Dr. Ahmed A. Khalil

4th year Civil4th year CivilWeek 13

Turnouts & Crossings in a Yard

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Electric Left Turnout

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Manual Handling Right Turnout

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Right and Left Turnouts

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Turnout Parts

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1- Switch part2- Middle (Lead) part3- Crossing part

-The long, continuous rails that form the outside edges of theswitch are called the stock rails.-The movable parts that route the trains one way or the otherare called the points or point blades. The throw bar or tiebar ties the points together and controls their movement fromside to side.-The crossing in the middle where the rails meet is called thefrog.

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frog.-The rails between the points and the frog are called theclosure rails.-The small lengths of rail along the stock rails (opposite thefrog) are called checkrails or guard rails. These keep thewheels from "picking the frog" and heading the wrong way,leading to a derailment.

On a typical switch, the straight path is called themain route, and the path that curves away iscalled the diverging route.

In a railroad, the sharpness of this divergent route

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In a railroad, the sharpness of this divergent routeis identified in one of two ways: either in termsof the radius, or by a number. The larger thefrog angle, the wider is the switch.

- A guard rail (check rail) is a short pieceof rail placed alongside the main (stock)rail opposite the frog.- These exist to ensure that the wheelsfollow the appropriate flangeway throughthe frog and that the train does not derail.- Generally, there are two of these for eachfrog, one by each outer rail.

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frog, one by each outer rail.

Turnout Operation

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Facing and Trailing

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- Points can be moved laterally into one of two positions soas to determine whether a train coming from the narrowend will be led towards the straight path or towards thediverging path.- A train moving from the narrow end towards the pointblades is said to be executing a facing-pointmovement.

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movement.

Unless the switch is locked, a train coming from either ofthe converging directs will pass through the points ontothe narrow end, regardless of the position of the points, asthe vehicle's wheels will force the points to move. Passagethrough a switch in this direction is known as a trailing-point movement.

Various factors limiting speeds over turnouts are as follows

A-Kink in the turnout route at the toe of switch railB-Entry from straight to curve without transitionC- Lead curve without super-elevationD-Entry from curve to straight without transitionE-Gap at the V of crossing

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Straight switchesStraight switches

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Partly curved switchesPartly curved switches

NonNon-- intersecting typeintersecting type

Intersecting typeIntersecting type

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Intersecting typeIntersecting type

Tangential typeTangential type

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Type s of crossing (Frog)Type s of crossing (Frog)

Straight crossingStraight crossing Curved crossingCurved crossing

lead curve may take one of the following forms:lead curve may take one of the following forms:1- Simple Circular Curve

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2- Partly Curved, having a straight length near the crossing3- Transition Curve

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-- AbbreviationsAbbreviationsto be usedto be used

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Representation of a turnout on centre lineRepresentation of a turnout on centre line

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On the centre line the turnout is represented by two lines OPN1 Wand PN2 Z. In this OW represents the overall length of turnout fromSJ to the heel of crossing along the gauge line on which the crossinglies. To locate the turnouts on centre line method, it will be necessaryto knowthe different components of centre line representation.

OP=APN1 =PN2 =MN1 W=N2 Z=KPW=PZ=B=M+KWhere A, M & K are known as turnout parameters

‘M’ is the distance from ‘P’ to the stock joint and can befound out as explained below:

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11-- Turnout with straight switchesTurnout with straight switches

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Offsets to Lead Curves forOffsets to Lead Curves forTurnout with StraightTurnout with StraightSwitchesSwitches

- The lead curve isextended from heel at point‘B’ to a point ‘H’ so thatthe tangent to the curveruns parallel to the gaugeline at a distance ‘Y’

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line at a distance ‘Y’

- The point ‘H’ has been shown to lie inside the track, but in certainlayouts, depending on the switch angle and the radius, the point ‘H’may lie outside the track and therefore the value of ‘Y’ will workout as negative. The distance ‘BQ’ be denoted by ‘L’

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ExampleExample

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22-- Turnout with CurvedTurnout with CurvedSwitchesSwitches

The lead curves in theselayouts at toe of switchesare tangential to theswitch angle and meetsthe straight leg of crossing

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the straight leg of crossingat a distance ‘w’ from theTNC of the crossing.

At toe of switch, thickness of tongue rail is ‘t’. Derivation forlead curve radius will be same as for straight switches. The samecan be derived by substituting ‘t’ (toe thickness) for ‘d’ (the heeldivergence).

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-- ExampleExample

Calculate the lead andthe radius of a 1 in 12turnout with curvedswitches.

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ApplicationsApplications

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Connections to Straight Parallel

Connections to Straight Parallel TracksConnections to Straight Parallel Tracks

Type of Layout connections between the straight parallel trackswill be dependent upon the distance between the two tracks andthe space availability in the yard. Accordingly distance betweenthe two tracks may be treated as Normal or Large distance.

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Tracks

Diamond CrossingDiamond Crossing

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- A crossover is a pair of switches that connects twoparallel rail tracks, allowing a train on one track to crossover to the other. Like the switches themselves,crossovers can be described as either facing or trailing.

- When two crossovers are present in opposite directions,one after the other, the four-switch configuration is

CrossoverCrossover

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one after the other, the four-switch configuration iscalled a double crossover.

Crossover Connection between Straight Parallel TracksCrossover Connection between Straight Parallel Tracks

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First of all the value of ‘D’ will be known from the field surveying.Turnout prarameters ‘A’, ‘B’ will be known once we have decidedthe type of turnout. Then from Eq 5.2 & 5.3, the values of ‘X’ &finally ‘OL’ will be calculated. Now with these values in the hand,location of one of ‘SJ’ can be fixed by keeping it at a distance ‘OL’apart in reference to another ’SJ’.After fixing the location of ‘SJ’, rest of the turnout can be set outby field surveying.

Scissors

If the crossovers overlap in the shape of the letter X, it isdubbed a ‘scissors crossover or diamond crossover’ inreference to the diamond crossing in the centre. This makesfor a very compact track layout at the expense of using alevel junction.

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The same function can be achieved by two crossoversFacing each other.

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Single SlipSingle Slip

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Double SlipDouble Slip

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Typical Yard DepotTypical Yard DepotLadder TracksLadder Tracks

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Flying JunctionsFlying JunctionsBridgesBridges

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Level JunctionsLevel JunctionsDiamond CrossingsDiamond Crossings

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Bridge Guard Rail

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