Zig zag (railway)

The Lithgow Zig Zag

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

Darjeeling Himalayan Railway, a UNESCO World Heritage site, with 6 full zig zags and 3 spirals

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] Not all switchbacks come in pairs, in which case the train may need to travel backwards for a considerable distance.

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]

One of the best examples is the Darjeeling Himalayan Railway, a UNESCO World Heritage site railway in India, that has six full zig zags and 3 spirals.^[4]

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.^[5]
• Reversing a locomotive-hauled 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.^[6]

Examples

• Argentina
  • Tren a las Nubes (1921)
• Australia
  • Lithgow Zig Zag, New South Wales (1869–1910) preserved - see Zig Zag Railway
  • Out of use:
    • Thornleigh Zig Zag, New South Wales^[7] (dismantled)
    • Yarraglen (dismantled)
    • Kalamunda Zig Zag, Western Australia – two reversals (dismantled)
    • Lake Margaret Tram, Tasmania, 610 mm (2 ft) (dismantled)
    • Lapstone Zig Zag, New South Wales – two reversals (1865) (dismantled)
    • Mundaring Weir Branch Railway, Western Australia (dismantled)
    • Yarloop, Western Australia (dismantled)
• Myanmar (also known as Burma)
  • Passenger line between Thazi and Kalaw, with four switchbacks; still in use
  • Passenger line between Mandalay and Lashio
• China
  • Qinglongqiao on the Jingbao Railway
  • Mifengyan on the Jiayang Coal Railway 762 mm (2 ft 6 in) - one reversal
• Chile
  • Pisagua – Three reversals; long out of use but earthworks easy to trace
• Denmark
  • 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.
• Ecuador
  • Sibambe on the Quito-Guayaquil line (cf. Empresa de Ferrocarriles Ecuatorianos)
• France
  • Froissy Dompierre Light Railway
• Germany
  • In use:
    • Rauenstein (Hinterland Railway)
    • Lauscha (Sonneberg – Probstzella railway)
    • Ernstthal am Rennsteig: created by close of the Ernstthal–Probstzella railway
    • Lüttmoorsiel-Nordstrandischmoor island railway
    • Rennsteig (Rennsteig Railway, Ilmenau – Themar)
    • Michaelstein (Rübeland Railway)
    • Wurzbach (Saalfeld – Blankenstein railway)
    • Altenkirchen station, Limburg–Altenkirchen railway
  • out of use
    • Schillingsfürst (dismantled)
    • Lenzkirch in the Black Forest (dismantled)
    • Elm (replaced in 1914 by Distelrasen Tunnel, but the structure is conserved within the Frankfurt-Fulda and Fulda-Gemünden railways and the connecting curve between the stations at Elm and Schlüchtern
    • Steinhelle-Medebach railway (double zig zag)
    • Mainspitze station in Frankfurt am Main, used from 1846–1848 to reach the provisional Frankfurt terminal of the Main-Neckar Railway (dismantled)
• Hungary
  • The Szob-Nagybörzsöny forest railway has a simple zig zag at the middle of the railway line between Kisirtás and Tolmács-hegy stations, with a loop in the middle of the Z shape
• India
  • Darjeeling Himalayan Railway has six full zig zags and 3 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
• Italy
  • Saline-Volterra (dismantled in 1958)
  • Ferrovia Genova-Casella has one zig zag currently in regular use at Casella Deposito.
• Japan
  • Hakone Tozan Line has three zig zags, namely at Deyama S.B., Ōhiradai Station, Kami-Ōhidradai S.B.
  • Hōhi Main Line at Tateno Station
  • Kisuki Line at Izumo-Sakane Station
  • Hisatsu Line at Okoba and Masaki stations
  • Tateyama Sabō Erosion Control Works Service Train, the work train for an erosion control construction, is not open to general public, but deserves a mention for its 38 zig zags, 18 of them in a row.
  • Niyama Station on Hakodate Main Line (see #Wartime type switchback)

The switchback between Tanballyŏng and Malhwiri

• North Korea
  • Kanggye Line, between Hwangp'o and Simrip'yŏng stations
  • Kŭmgangsan Electric Railway, between Tanballyŏng and Malhwiri (Kŭmganggu) stations. Entire line destroyed during the Korean War and not rebuilt.
  • Paengmu Line, between Yugok and Rajŏk stations, and at Samyu station (station is located on a single reverse)
  • in addition, there are numerous switchbacks on spurs into underground facilities located off main lines.
• South Korea
  • Yeongdong Line, between Heungjeon station and Nahanjeong station. This section closed in 2012 and replaced by Solan tunnel .
• México
  • Ferrocarril Noroeste de México, between Juan Mata Ortiz to Chico.
• New Zealand
  • Driving Creek Railway, Coromandel
• Pakistan
  • Khyber Pass
• Peru
  • Seven full Zigzags and one single reverse on the Central Railway of Peru
  • PeruRail between Cuzco to Machu Picchu – Five switchbacks
• Slovakia
  • Historical Logging Switchback Railway in Vychylovka
• Sweden
  • Lövsjöväxeln (Lövsjö points) on Hällefors-Fredriksbergs Järnvägar (1875–1940)^[8]

SBB A 3/5 on the turntable at Chambrelien

• Switzerland
  • Chambrelien required the use of a turntable to allow large tender locomotives to be turned as they ran-round their trains.
• Taiwan
  • Alishan Forest Railway
• United States
  • Hagans Switchback in Virginia
  • Eight switchbacks at Cascade on GN – Replaced by tunnel which was in turn replaced by a longer tunnel
  • Cass Scenic Railroad, West Virginia – Two switchbacks with 11% grade between, still in use
  • Confusion Hill Mountain Train Ride, Piercy, California – Several switchbacks in use
  • Industrial switchback, Montage Mountain Road, Scranton, Pennsylvania – Still in use
  • Mount Hood Railroad, Hood River, Oregon – One switchback, still in use
  • Roaring Camp and Big Trees Narrow Gauge Railroad, Felton, California – One switchback, still in use
  • Shasta Sunset Dinner Train, McCloud, California – One switchback, "Signal Butte Switchback", in use
  • Buckingham Branch Railroad, New Canton, Virginia – One switchback at New Canton
  • Fern Rock Transportation Center, Fern Rock, Philadelphia - One switchback, connects the Broad Street Line with SEPTA Regional Rail, still in limited use
  • Sierra Railway, Melones, California - Two switchbacks, abandoned, used by SRY's Angels Branch to cross Stanislaus River Canyon, one switchback inundated by New Melones Lake

References