Track gauge conversion
|Track gauge · Break-of-gauge · Dual gauge ·
Conversion (list) · Bogie exchange · Variable gauge
|By transport mode|
|Tram · Rapid transit · High-speed rail|
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|North America · South America · Europe|
In rail transport, gauge conversion is the process of converting a railway from one rail gauge to another, through the alteration of the railway tracks. An alternative to gauge conversion is dual gauge track, or gauge conversion of the rail vehicles themselves.
Ideally railways should all be built to the same gauge, since a wide range of gauges from narrow to broad are of similar value in carrying heavy loads at low cost, while small differences of gauge create tremendous break-of-gauge costs and inconvenience.
Rail vehicles 
Gauge conversion of coaches and wagons involves the replacement of the wheelsets or entire bogies, such as happened when the 7 ft 1⁄4 in (2,140 mm) gauge of the Great Western Railway was abandoned in May 1892. Where vehicles regularly work to and fro across a permanent change of gauge, for example between the 4 ft 8 1⁄2 in (1,435 mm) system in France and the 1,668 mm (5 ft 5 2⁄3 in) in Spain, stations are equipped with special bogie exchange equipment. Some vehicles nowadays are fitted with variable gauge axles which do not require any exchange of the wheelsets, but still require special equipment. This temporary alteration to allow through working is generally referred to as "gauge change".
Steam locomotives are difficult to convert unless this is already allowed for in the design, such as in some East African Railways Garratts, and in steam locomotives built for Victoria after 1930s. In the event, few have been so converted, but one such is Victorian Railways R class R766.
Sleeper types 
Often gauge convertible sleepers are installed before the conversion of the rails themselves. Sleepers have to be long enough to take the wider of the gauges, and secondly, the sleepers must be able to take the fittings of both gauges. Gauge convertibility can also be a stepping stone to dual gauge. In cases where the differences between the gauges are small, such as 1,000 mm (3 ft 3 3⁄8 in)/1,067 mm (3 ft 6 in) and 1,435 mm (4 ft 8 1⁄2 in)/1,524 mm (5 ft), dual gauge with a third rail is not practicable, in these cases four rail dual gauge is necessary.
- Timber sleepers, provided that they are long enough, are always gauge convertible, since additional holes for the dogspikes can always be drilled later. If the new gauge is wider than the old, a shorter than normal sleeper can be tolerated to a degree.
- Concrete sleepers cannot be converted as an afterthought, but must have the future fittings cast in place when manufactured.
- Steel sleepers should have the extra fitting incorporated when manufactured, though it might be possible to drill or weld the fitted sleeper after installation with some difficulty.
Loading gauge 
Narrow gauge railways often have a significantly smaller loading gauge in both height and width. Conversion to a wider track gauge will often require enlargement of the loading gauge, by raising bridges and enlarging tunnels, if any.
The minimum radius curve of a narrow gauge railway is often less than a wider gauge, which may require deviations to ease such curves.
Track centres at stations with multiple tracks will also have to be widened. This would be less of a problem on the usually single track main lines of the narrow gauge railway.
Gauge orphan 
During gauge conversion work such as between Seymour and Albury, branch lines such as Benalla to Oaklands and stations such as Violet Town become gauge orphans as they cannot easily be served by trains until extra costly work is done.
Track gauge conversion 
Conversion rate 
Rolling stock 
Because boilers and fireboxes are in the way (unless allowed for) locomotives can be converted only to a wider gauge.
About 1860, the Yeovil to Taunton Railway converted six 1,435 mm (4 ft 8 1⁄2 in) gauge locomotives to 2,140 mm (7 ft 1⁄4 in) gauge, and later converted them back again.
In the 19th century, in the US, some broad 1,524 mm (5 ft) gauge locomotives were designed for easy conversion to 1,435 mm (4 ft 8 1⁄2 in) gauge.
In the 20th century, in Victoria, some broad 1,600 mm (5 ft 3 in) gauge locomotive classes were designed for easy conversion to 1,435 mm (4 ft 8 1⁄2 in) gauge.
Between 1922 and 1949, five South Australian Railways T class narrow 1,067 mm (3 ft 6 in) gauge locomotives were converted to Tx-class broad 1,600 mm (5 ft 3 in) gauge, and later back again.
Waggons and Carriages 
In 1941, there were plans to regauge 1,435 mm (4 ft 8 1⁄2 in) gauge steam locomotives to the 1,524 mm (5 ft) gauge.
See also 
|Wikimedia Commons has media related to: Manual gauge changing|
|Wikimedia Commons has media related to: Automated gauge changing|
- Gauge conversion in the US
- List of gauge conversions
- Project Unigauge, an ongoing project on Indian Railways to convert almost all railways in India to 5 ft 6 in Indian gauge
- Variable gauge