Zig zag (railway)

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Zig zag to cross the outer dyke on the railway serving the island of Nordstrandischmoor off the German North Sea coast.
Switchback of the Cecina-Volterra railway(it)

A railway zig zag, also called a switchback, is a way of climbing hills in difficult country with a 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 e.g. to ascend very steep gradients by using a zig-zag alignment at which trains have to reverse direction in order to continue is a reversing station.[3]

Advantages[edit]

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[edit]

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[edit]

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]

Location of zig zags[edit]

References[edit]

  1. ^ Raymond, William G. (1912). "Railway Engineering". In Beach, Frederick Converse. The Americana: A Universal Reference Library, Comprising the Arts and Sciences, Literature, History, Biography, Geography, Commerce, Etc., of the World (Google books) 17. New York: Scientific American Compiling Department. Retrieved 3 January 2010. High mountain levels … may be tunneled … but … may be reached by one of several methods adopted to secure practical grades: (1) Zig-zag development … (2) Switchback development … (3) Spirals or loops … 
  2. ^ Raymond 1912. "Switch-back development … necessitating the use of switches at these ends and the backing of the train up alternate stretches."
  3. ^ Jackson, Alan A. (2006). The Railway Dictionary, 4th ed., Sutton Publishing, Stroud, p. 285. ISBN 0-7509-4218-5.
  4. ^ "The Zig-Zag Deviation.". The Dubbo Liberal and Macquarie Advocate (NSW : 1892 - 1927) (NSW: National Library of Australia). 5 December 1908. p. 4. Retrieved 17 February 2013. 
  5. ^ "The Railway Accident on the Zig-zag.". Bathurst Free Press and Mining Journal (NSW : 1851 - 1904) (NSW: National Library of Australia). 10 April 1895. p. 3. Retrieved 19 February 2013. 
  6. ^ "Historical and Archaeological Assessment of Proposed Cycleway, Near Thornleigh Quarry, Via De Saxe Close, Thornleigh (Berowra Valley Regional Park), N.S.W.". The construction of the railway siding and zig-zag to the quarry and also Hall’s Camp were associated with Amos & Co, who won the contract to build the section of railway from Strathfield to Hawkesbury River. Edward Higginbotham & Associates PTY LTD. Retrieved 15 March 2013.