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Construction methods
The Alishan Forest Railway is an industrial railway built to cultivate forest resources or develop the forest landscapes along the railway into tourism resources. Besides a forest railway, The Alishan Forest Railway is an uphill railway and a mountain railway at the same time.
The world's five basic methods of uphill railway construction
  In general, to overcome slope resistance, it is necessary to build special engines for trains to cross over slopes and turns and to reduce railway construction cost. Difficulties that cannot be overcome by rolling stock modification are resolved by trackwork, so as to overcome the high slope grade and big curve problems.
For uphill railway construction in the 19th century, as train horsepower was limited, the following five construction methods were developed to enable trains to climb over mountains.
(1) S-type line and U-turn line
(2) Loop line and spiral route
(3) Rack railway (cog rail)
(4) Switch back (zigzag)
(5) Special engine (locomotive)
Four of these five methods are found on the Alishan Forest Railway
  S-type line and U-turn line
To reduce track slope grade, uphill railways are built in the mountain valley or between rivers, and sometimes, it needs to take a U-turn (180°).
As the elevation rises, this type of turn is also called the Ω-type turn. It is the most common method used on uphill railways across the world.
Along The Alishan Forest Railway, a typical U-turn is found in the section between Jhuci and Mulyuliao at 17.1K.
Loop line and spiral route
  Uphill railways are built in the loop or spiral shape, sometimes many rounds, to climb upward (elevation rise). When the route circulates one round (360°)
concentrically, it is called a loop line. When it circles many times eccentrically or irregularly, it is called a spiral route.
At the spiral section on Mt. Duli of the Alishan Forest Railway, passengers can see the same view three times at different heights.
Switch back (zigzag)
  To reduce track slope grade for an uphill train, when there is not enough space for an s-type line or U-turn line, nor is a loop line or spiral route feasible, trains can only go back and forth repeatedly to climb upward, like climbing up the stairs. In general, a switchback or zigzag will significantly affect train formation and running speed. Therefore, this is the last choice of all solutions.
The zigzag section of the Alishan Forest Railway is the most famous in Taiwan. When the train enters the zigzag section of the first diverging rail, it goes up from the right and down on the left to climb up the mountain.
Special engine (locomotive)
  Special engines (locomotives) were invented when steam trains could not negotiate with the rough track with sharp curve and steep grade on some uphill railways or forest railways in earlier times. With the rise of diesel engines and electric engines in the 20th century, most special engines were eliminated. Most special engines are operated today for preserving railway cultural assets.
Value of the Alishan Forest Railway
  The Alishan Forest Railway has the most sophisticated complexity.
It combines the features of a forest railway, an uphill railway, and a mountain railway all in one. Except for the rack railway, nearly all features are found in it: the zigzag line, spiral route, and special engine (cylinder vertical engine).
In other words, The Alishan Forest Railway has technological diversity, making it eligible for a world cultural heritage. The Alishan Forest Railway is the highest narrow-gauged uphill railway in Asia. It is also very likely the world's highest among all operating railways. The rail gauge of the Alishan Forest Railway is 762mm, and Zuhshan Station is located at 2,451m in elevation. It is thus higher than the highest point at Ghum of 2,257m in elevation of the narrow-gauged (600mm) Darjeeling Himalayan Railway in India. The Alishan Forest Railway is the narrow-gauged (762mm) uphill railway with the highest elevation gain (2,421m) in the world compared to the famous non-rack uphill railways in the world, such as the Darjeeling Himalayan Railway with an elevation gain of 2,144m. "Elevation gain" refers to the height of the vertical rise of an uphill railway. Like a magical xpresscalator, the "elevation gain" is obtained by subtracting the altitude of the highest and lowest points. The Alishan Forest Railway the non-rack and non-electric narrow-gauged (762mm) uphill railway is the steepest grade in the world. In uphill or funicular railways, "route slope grade"
symbolizes the difficulty and risk of climbing up the mountain. Like pushing a car upslope, the greater the slope grade is, the higher the risk will be. Conversely, the climbing performance of trains is better.
  Source: Su, Z. X. (2012). 100 Years Anniversary of the Alishan Forest Railway: Legend of the Alishan Forest Railway through Hundred Years. Taipei: Forestry Bureau, Council of Agriculture.