A railway zig zag, also called a switchback, is a method of climbing steep gradients with minimal need for tunnels and heavy earthworks. 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.
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.
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.
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.
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.
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.
Argentina
Tren a las Nubes (1921)
Australia
Lithgow Zig Zag (rail line) (1869-1910) (see Zig Zag Railway) (preservation society) (1975-))
Out of use:
Thornleigh Zig Zag
Yarraglen (dismantled)
Kalamunda Zig Zag – Two reversals
Lapstone Zig Zag – Two reversals (1865)
Mundaring Weir Branch Railway
Yarloop, Western Australia (dismantled)
Lake Margaret Tram 610 mm (2 ft)
Burma (also known as Myanmar)
Passenger line between Thazi and Kalaw, with four switchbacks; still in use
Passenger line between Mandalay and Lashio
China
Qinglongqiao on the Jingbao Railway
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
Nagybörzsönyi Erdei Vasút 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, narrow gauge
India
Darjeeling Himalayan Railway has six full zig zags, 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, narrow gauge
Italy
Saline-Volterra (dismantled in 1958)
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)
South Korea
Yeongdong Line, between Heungjeon station and Nahanjeong station. This section closed in 2012 and replaced by Solan tunnel .
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)
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
