Editing Track gauge (section)

==Advantages and disadvantages of different track gauges==
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Speed, capacity, and economy are generally objectives of rail transport, but there is often an inverse relationship between these priorities. There is a common misconception that a narrower gauge permits a tighter turning radius, but for practical purposes, there is no meaningful relationship between gauge and curvature.<ref>{{Cite book | last = Wellington | first = Arthur | title = The Economic Theory of the Location of Railways | publisher = John Wiley & Sons | date = 1910 | location = New York | pages = 751–754}}</ref><ref>{{cite journal | last =Siddall | first = William | title = Railroad Gauges and Spatial Interaction | journal = Geographical Review | volume = 59 | issue = 1 | page = 36 | publisher = American Geographical Society | date = January 1969 | jstor = 213081 | doi = 10.2307/213081| bibcode = 1969GeoRv..59...29S }}</ref>

===Construction cost===
Narrower gauge railways usually cost less to build because they are usually lighter in construction, using smaller [[railway car|cars]] and [[locomotive]]s (smaller [[loading gauge]]), as well as smaller [[bridge]]s, smaller [[tunnel]]s (smaller [[structure gauge]]).<ref>{{cite book |first=Charles Easton |last=Spooner |url=https://books.google.com/books?id=3pUpAAAAYAAJ&pg=PA71 |title=Narrow Gauge Railways |date=1879 |page=71}}</ref> Narrow gauge is thus often used in mountainous terrain, where the savings in [[civil engineering]] work can be substantial. It is also used in sparsely populated areas, with low potential demand, and for temporary railways that will be removed after short-term use, such as for construction, the logging industry, the mining industry, or large-scale construction projects, especially in confined spaces (see [[Track gauge#Temporary way – permanent way|Temporary way – permanent way]]).

For temporary railways which will be removed after short-term use, such as those used in logging, mining or large-scale construction projects, especially in confined spaces, such as when constructing the [[Channel Tunnel]], a narrow-gauge railway is substantially cheaper and easier to install and remove. Such railways have almost vanished due to the capabilities of modern [[truck]]s. In many countries, narrow-gauge railways were built as branch lines to feed traffic to standard-gauge lines due to lower construction costs. The choice was often not between a narrow- and standard-gauge railway, but between a narrow-gauge railway and none at all.

Broader gauge railways are generally more expensive to build, because they are usually heavier in construction, use larger [[railway car|cars]] and [[locomotive]]s (larger [[loading gauge]]), as well as larger [[bridge]]s, larger [[tunnel]]s (larger [[structure gauge]]). But broader gauges offer higher speed and capacity. For routes with high traffic, greater capacity may more than offset the higher initial cost of construction.

===Interchangeability===
The [[Value (economics)|value]] or [[utility]] a user derives from a [[Goods|good]] or [[Service (economics)|service]] depends on the number of users of compatible products – the "[[network effect]]" in economics. Network effects are typically positive, resulting in a given user deriving more value from a product as other users join the same network.<ref>{{Cite book|last=Shapiro, Carl.|url=https://www.worldcat.org/oclc/39210116|title=Information rules : a strategic guide to the network economy|date=1999|publisher=Harvard Business School Press|others=Varian, Hal R.|isbn=0-87584-863-X|location=Boston, Mass.|oclc=39210116}}</ref> At national levels, the network effect has resulted in commerce extending beyond regional and national boundaries. Increasingly, many governments and companies have made their railways' engineering and operational standards compatible in order to achieve interchangeability – hence faster, longer-distance train operation. A major barrier to achieving interchangeability, however, is [[path dependence]]<ref>{{cite book |last1=Liebowitz |first1= S. |last2=Margolis |first2= Stephen |title= Encyclopedia of Law and Economics |year= 2000 |isbn= 978-1-85898-984-6 |page= 981 |publisher= E. Elgar }}</ref> – in this context the persistence of an already adopted standard to which equipment, infrastructure and training has become aligned.

Since adopting a new standard is difficult and expensive, continuing with an existing standard can remain attractive, unless longer-term benefits are given appropriate weight. An example of the consequences of path dependence is the persistence in the [[United Kingdom]] – the earliest nation to develop and adopt railway technologies – of [[structure gauge]]s that are too small to allow the larger [[rolling stock]] of continental Europe to operate in the UK. The reduced cost, greater efficiency, and greater economic opportunity offered by the use of a common standard has resulted in the historical multitude of track gauges dwindling to a small number that predominate worldwide.

When interchangeability has not been achieved, freight and passengers must be transferred through time-consuming procedures requiring manual labour and substantial capital expenditure.<ref>{{cite book |url=https://books.google.com/books?id=8OVGAQAAMAAJ&pg=RA1-PA200 |title=Irish Railways including Light Railways (Vice-Regal Commission |date=1908 |volume=XLVII |page=200 |publisher=House of Commons |location=London)}}</ref> Some bulk commodities, such as [[coal]], [[ore]], and [[gravel]], can be mechanically [[Transshipment|transshipped]], but even this is time-consuming, and the equipment required for the transfer is often complex to maintain. If rail lines of different gauges coexist in a network and a [[break of gauge]] exists, it is difficult in times of peak demand to move rolling stock to where it is needed.

Sufficient rolling stock must be available to meet a narrow-gauge railway's peak demand, which might be greater in comparison to a broader-gauge network, and the surplus equipment generates no cash flow during periods of low demand. In regions where narrow-gauge lines form a small part of the rail network (as was the case on Russia's [[Sakhalin Railway]]), extra cost is involved in designing, manufacturing or importing narrow-gauge equipment.

Solutions to interchangeability problems include [[bogie exchange]]s, a [[rollbock]] system, [[dual gauge]], [[variable gauge]], or [[gauge conversion]].