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Zig zag (railway)

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Title: Zig zag (railway)  
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Subject: Spiral (railway), Ruling gradient, Lithgow Zig Zag, Lüttmoorsiel-Nordstrandischmoor island railway, Lapstone Zig Zag
Collection: Railway Track Layouts
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Zig zag (railway)

Zig zag to cross the outer dyke on the railway serving the island of Nordstrandischmoor off the German North Sea coast
Zig zag of the Cecina-Volterra railway

A railway zig zag, also called a switchback, is a method of climbing steep gradients with minimal need for tunnels and heavy earthworks.[1] For a short distance (corresponding to the middle leg of the letter "Z"), the direction of travel is reversed, before the original direction is resumed.[2]

A location on railways constructed by using a zig-zag alignment at which trains have to reverse direction in order to continue is a reversing station.[3]

Contents

  • Advantages 1
  • Disadvantages 2
  • Hazards 3
  • Examples 4
  • References 5

Advantages

Zig zags tend to be cheaper to construct because the grades required are discontinuous. Civil engineers can generally find a series of shorter segments going back and forth up the side of a hill more easily and with less grading than they can a continuous grade which has to contend with the larger scale geography of the hills to be surmounted.

Disadvantages

Zig zags suffer from a number of limitations:

  • The length of a train is limited to what will fit on the shortest stub track in the zig zag. The Lithgow Zig Zag stub was extended at great cost in 1908, only to be completely deviated in 1910.[4]
  • Reversing a train without running an engine around to the rear of the train is hazardous. Top and tail or push pull operation with engines at the rear of the train helps.
  • The process is slow due to the need to stop the train after each segment and reverse the switch.
  • It is by nature a single track configuration.

Hazards

If wagons in a freight train are marshalled poorly, with a light vehicle located between heavy ones (particularly with buffer couplings), the move on the middle road of a zig zag can cause derailment of the light wagon.[5]

Examples

References

  1. ^
  2. ^ Raymond 1912. "Switch-back development … necessitating the use of switches at these ends and the backing of the train up alternate stretches."
  3. ^
  4. ^
  5. ^
  6. ^
  7. ^ http://www.ekeving.se/b/HFJ/bgdskisser/
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