Australia: theLithgow Zig Zag, 2008Germany: zig zag required to cross the outer dyke on therailway serving the island ofNordstrandischmoor, 2010India: theDarjeeling Himalayan Railway, aUNESCOWorld Heritage Site, with six full zig zagsItaly: zig zag on the Cecina-Volterra railway, 1938Japan: Obasute Station platform sign displaying the switchback, 2018North Korea: switchback between Tanballyŏng and Malhwiri, 1931Switzerland:SBB A 3/5 locomotive on the turntable at Chambrelien railway station, before 1931
Arailwayzig zag orswitchback is a railway operation in which a train is required to switch its direction of travel to continue its journey. While this may be required purely from an operational standpoint, it is also ideal for climbing steep gradients with minimal need fortunnels and heavyearthworks.[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] Some switchbacks do not come in pairs, and the train may then need to travel backwards for a considerable distance.
A location on railways constructed by using a zig-zag alignment at which trains must reverse direction to continue is areversing station.[3]
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 for continuous grade, which must contend with the larger-scale geography of the hills to be surmounted.
The length of trains is limited to what will fit on the shortest stub track in the zig zag. For that reason, theLithgow Zig Zag's stubs were extended at great expense in 1908.[5] Even then, delays were such that the zig zag had eventually to be bypassed by a new route, which opened two years later.
Reversing a locomotive-hauled train not purposely equipped forpush-pull operation without first running the engine around to the rear of the train can be hazardous; however, operating the train with two locomotives, one at each end (a practice known as "topping-and-tailing"), can mitigate the dangers.
The need to stop the train after each segment, throw the switch, and reverse means that progress through the zig zag is slow.
Passenger cars with transverse seating force riders to travel in reverse for at least part of the journey though that issue is largely solved by longitudinal seating on cars serving such routes.[6]
If the wagons in a freight train are marshaled poorly, with a light vehicle located between heavier ones (particularly withbuffer couplings), the move on the middle road of a zig zag can causederailment of the light wagon.[7]
Dubí – local railway between Moldava and Most (Most–Moldava railway), trains have to change direction in Dubí station to continue further. Only one halt of a 'Z' is placed
Lemvig – Small side track from the harbor to the railway station, used only on special occasions. In reality, only half a 'Z' as only one reversal is needed.
Darjeeling Himalayan Railway has six full zig zags and three spirals. Most are from the construction of the current railway, but one was added in the 1940s, and at least one other was used temporarily following storm damage
Western Line, Auckland. Service runs fromBritomart toNewmarket before reversing to run toSwanson. The reverse could be avoided, but that would bypass Newmarket, which is a major station.
Tierkrans Switchback Railway, between Barkley East station and Aliwal-North station. For economic reasonsm regular service was finally discontinued in 1991. Railway enthusiasts also know the line for the famous set of eight reverses.
^Raymond, William G. (1912)."Railway Engineering"(Google books). In Beach, Frederick Converse (ed.).The Americana: A Universal Reference Library, Comprising the Arts and Sciences, Literature, History, Biography, Geography, Commerce, Etc., of the World. Vol. 17. New York: Scientific American Compiling Department. Retrieved3 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 …
^Raymond 1912. "Switch-back development … necessitating the use of switches at these ends and the backing of the train up alternate stretches."
^Jackson, Alan A. (2006).The Railway Dictionary (4th ed.). Stroud: Sutton Publishing. p. 285.ISBN0-7509-4218-5.
