A double junction (Fig. 15.17) is required when two or more main line tracks are running and other tracks are branching off from these main line tracks in the same
direction. The layout of a double junction consists of ordinary turnouts with one or more diamond crossings depending upon the number of parallel tracks.
Double junctions may occur either on straight or curved main lines and the branch lines may also be either single or double lines. These types ofjunctions are quite common in congested yards.
Track junctions are required to transfer railway vehicles from one track to another or enable a train to cross a track. Several types of junctions can be laid using different combinations of points and crossings. The commonly used layouts have been discussed in this chapter with the help of sketches and solved examples.
1. A BG turnout takes off a straight track, with a 1 in 12 crossing. Given: heel divergence (d) is 13.3 cm, distance between TNC and tangent point of crossing (w) is 1.346, angle of crossing (a) and switch angle (b) are 4° 45'49" and 1° 9 0", respectively. Calculate the lead of the turnout and the radius of the curve. What would be the lead if no straight length is provided at the crossing?
2. A BG branch line takes off in contrary flexure through a 1 in 12 turnout from the main line. The maximum permissible speed on the branch line is 40 km/h. Calculate the negative superelevation to be provided on the branch line and the maximum permissible speed on the main line (the degree of turnout curvature for the 1 in 12 crossing is about 4°).
3. Write short notes on the following.
(a) Gathering line
(b) Scissors crossover
4. What is a crossover? A crossover with a 1 in 12 turnout and a straight intermediate portion is to be laid between two parallel straight broad gauge tracks. Determine the various design elements.
5. Draw a neat sketch of a right-hand crossover between two parallel straight railway tracks and list the principal components and terms connected with its layout.
6. Draw a neat sketch of a symmetrical split of a railway track.
7. Draw a neat sketch of a diamond crossing and list its important features.
8. Two parallel railway lines are to be connected by a reverse curve, each section having the same radius. The centre lines of the two tracks are 8 m apart and the maximum distance between the tangent points is 32 m. Find the maximum allowable radius that can be used.
9. Sketch a typical diamond crossing and label all its components. Design a diamond crossing between two BG tracks crossing each other at an angle of 1 in 10.
10. A turnout takes off a 4° curved BG track in contrary flexure. What would be the degree of curvature for the turnout, if a 1 in 8.5 crossing is used? Explain why a square Diamond Crossing is not very desirable.
11. Draw a scissors crossover showing the different rail pieces and gaps distinctly.
12. Calculate the (a) lead distance, (b) radius of the curved lead rail, and (c) overall length of the crossover installed between two BG straight parallel tracks spaced at 5 m from centre to centre. Two 1 in 12 crossings are connected by an intermediate straight track in this layout. Also make a dimensioned sketch of the crossover in question, properly labelling the wing rail, switch rails, and crossing angle.