Gauge change
Gauge conversion is a process of rail transport, which involves converting a railway from one rail gauge to another by altering the railway tracks. Alternatives to track gauge conversion include the use of a dual gauge track—avoiding the need of a conversion system—or adding a gauge conversion system to the rail vehicles, instead of the track.
Rails may be too light for the loads imposed by broader-gauge rail cars, and may need to be replaced with a heavier rail profile.
If the conversion involves the track gauge being narrowed, the existing sleepers can often still be used, but if the gauge is being increased, the sleepers used for the narrower gauge may be too short and will 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 practical. In those cases, gauntlet track is required.
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.
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