Track gauge conversion
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|By transport mode|
|Tram · Rapid transit
Miniature · Scale model
|By size (list)|
|Change of gauge|
|Break-of-gauge · Dual gauge ·
Conversion (list) · Bogie exchange · Variable gauge
|North America · South America · Europe · Australia|
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.
Rails may be too light for the loads imposed by broader-gauge railcars and need to be replaced with a heavier rail profile.
If the conversion involves the track gauge being narrowed, the existing sleepers can often continue to be used, but if the gauge is being increased, the sleepers used for the narrower gauge may be too short, and need to be replaced with longer ones.
In some cases, gauge-convertible sleepers are installed before the conversion of the track itself. The sleepers must be long enough to take the wider of the two gauges, and must be able to accommodate the fittings for both the existing and the new gauges. In cases where the difference between the two gauges is small, such as 1,000 mm (3 ft 3 3⁄8 in) and 1,067 mm (3 ft 6 in) track, or 1,435 mm (4 ft 8 1⁄2 in) and 1,524 mm (5 ft) track, providing dual-gauge track using a third rail is not practicable. In those cases, gauntlet track is required.
- Timber sleepers are always gauge convertible, provided that they are long enough, because new holes for the repositioned dogspikes can be drilled into them. If the new gauge is wider than the old, a shorter sleeper than would normally be used can be tolerated, provided it still allows for secure fastening of the wider track.
- 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 is theoretically possible to drill or weld new fittings to the sleeper after installation.
During the conversion of the Melbourne–Adelaide railway in Australia from 5 ft 3 in (1,600 mm) to 4 ft 8 1⁄2 in (1,435 mm), dual-gauging of the track was not possible because the foot of the heavy rails being used was too wide to allow them to be placed sufficiently close together. A special gauge-convertible sleeper, with a reversible chair for the Pandrol clip, allowed a two-week conversion process.
In June 2008, the South Australian government announced that by 2012 the Adelaide metropolitan network would be converted from 1,600 mm broad gauge to standard gauge. Consequently, broad-gauge timber sleepers are progressively being replaced with gauge-convertible concrete sleepers on the metropolitan rail network. As of 2016[update], however, gauge conversion had not commenced, and financial constraints seem likely to delay the program for the foreseeable future.
Narrow-gauge railways often have a significantly smaller structure gauge, and therefore the rolling stock used has a smaller loading gauge in both height and width. Conversion to a wider track gauge will often require enlargement of the structure gauge on bridges, under road overpasses and in tunnels. Embankments and cuts could need widening as well.
The minimum curve radius of narrow-gauge railways is often less than on tracks with a wider gauge, so route deviations might be required to allow the radius of curves to be increased. Track centres at stations with multiple tracks may also have to be increased.
Where vehicles cross a change of gauge, they must either be equipped for a change of bogie or have adjustable gauge axles. For example passenger trains crossing between the 1,435 mm (4 ft 8 1⁄2 in) system in France and the 1,668 mm (5 ft 5 21⁄32 in) in Spain pass through a special installation which adjusts their variable gauge axles. 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 the 1930s. In the event, few have been so converted, but one such is Victorian Railways R class R766.
Because boilers and fireboxes are in the way (unless allowed for) locomotives can be converted only to a wider gauge.
About 1860, the Bristol and Exeter Railway converted five 1,435 mm (4 ft 8 1⁄2 in) gauge locomotives to 7 ft (2,134 mm) 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 the narrower 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.
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.
Post WWII, a number of captured German 03 class pacifics were regauged to the Russian gauge.
Diesel & electric
Most diesel and electric which rest on bogies can be converted by replacing those bogies. Engines with fixed wheelbases are problematic.
In Australia, diesel locomotives are regularly regauged between broad, standard and narrow gauges.
Wagons and coaches
Gauge conversion of wagons and coaches 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.
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.
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