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| Gauge conversion (list) - Bogie exchange - Variable gauge | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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.
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Gauge conversion of coaches and wagons involves the replacement of the wheelsets or entire bogies, such as happened when the 7 ft 0 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.
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.
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.
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.
In this instance, the loading gauge of the broad gauge and standard gauge lines are essentially the same.
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