Variable gauge

Track gauge

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Minimum   Minimum   Fifteen inch 381 mm (15 in) Narrow   600 mm Two foot Two foot three inch 600 mm 610 mm 686 mm (1 ft 11+5⁄8 in) (2 ft) (2 ft 3 in)   750 mm Bosnian gauge Two foot six inch 750 mm 760 mm 762 mm (2 ft 5+1⁄2 in) (2 ft 5+15⁄16 in) (2 ft 6 in)   Swedish three foot 900 mm Three foot Italian metre 891 mm 900 mm 914 mm 950 mm (2 ft 11+3⁄32 in) (2 ft 11+7⁄16 in) (3 ft) (3 ft1+13⁄32 in)   Metre 1,000 mm (3 ft 3+3⁄8 in)   Three foot six inch 1,067 mm (3 ft 6 in)   Four foot 1,219 mm (4 ft)   Four foot six inch 1,372 mm (4 ft 6 in)   1432 mm 1,432 mm (4 ft 8+3⁄8 in)   Standard 1,435 mm (4 ft 8+1⁄2 in) Broad   Italian broad gauge Dresden gauge 1,445 mm 1,450 mm (4 ft 8+7⁄8 in) (4 ft 9+3⁄32 in)   Leipzig gauge 1,458 mm (4 ft 9+13⁄32 in)   Toronto gauge 1,495 mm (4 ft 10+7⁄8 in)   1520 mm Five foot 1,520 mm 1,524 mm (4 ft 11+27⁄32 in) (5 ft)   Pennsylvania gauge Pennsylvania gauge Five foot three inch 1,581 mm 1,588 mm 1,600 mm (5 ft 2+1⁄4 in) (5 ft 2+1⁄2 in) (5 ft 3 in)   Baltimore gauge 1,638 mm (5 ft 4+1⁄2 in)   Iberian gauge Five foot six inch 1,668 mm 1,676 mm (5 ft 5+21⁄32 in) (5 ft 6 in)   Six foot 1,829 mm (6 ft)   Brunel 2,140 mm (7 ft 1⁄4 in)
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A variable gauge system allows railway vehicles in a train to travel across a break of gauge between two railway networks with different track gauges. For through operation, a train must be equipped with special bogies holding variable gauge wheelsets which contain a variable gauge axle (VGA).

The gauge is altered by driving the train through a gauge changer or gauge changing facility. As the train passes through the gauge changer, the wheels are unlocked, are moved closer together, or further apart, and are then re-locked. Installed variable gauge systems exist within the internal network of Spain, and are installed on international links between Spain/France (Spanish train), Sweden/Finland (Swedish train), Poland/Lithuania (Polish train) and Poland/Ukraine (Polish train).

A system for changing gauge without the need to stop is in widespread use for passenger traffic in Spain,^[1] for services run on a mix of dedicated high-speed lines (using Standard gauge) and older lines (using Iberian gauge).^[2] Similar systems for freight traffic are still in their infancy, as the higher axle weight increases the technological challenge. Although several alternatives exist, including transferring freight, replacing individual wheels and axles, bogie exchange, transporter flatcars or the simple transshipment of freight or passengers, they are impractical, thus a cheap and fast system for changing gauge would be beneficial for cross-border freight traffic.^[3]

Alternative names include Gauge Adjustable Wheelsets (GAW), Automatic Track Gauge Changeover System (ATGCS/TGCS), Rolling Stock Re-Gauging System (RSRS), Rail Gauge Adjustment System (RGAS), Shifting wheelset,^[4] Variable Gauge Rolling Truck,^[5] track gauge change and track change wheelset.