Spanish Train Maker Talgo has unique VGA technology ie Variable Gauge Axle for multi gauge operation of train. The Spanish Broad Gauge or the Iberian Gauge is 1668 mm wide and it is slightly shorter (by 8mm) than Indian BG which is 1676 mm apart. In the neighbouring France, the SNCF railway system uses 1435 mm Standard Gauge also known as Stephenson Gauge named after the English railway pioneer George Stephenson who used the 4 ft 8 1⁄2 in gauge (including a belated extra 1⁄2 in (13 mm) of free movement to reduce binding on curves for the Liverpool and Manchester Railway that opened in September 1830. 55% of world railway uses SG. In India most Metro lines (except Red, Yellow & Blue lines of DMRC) and Calcutta tramways uses Standard Gauge.
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trains from Spain to France has a break of gauge that could cause a hindrance for international travellers to change trains at border crossings...but now it is not so......thanks to VGA that enables the same train to run on different track gauges without having to change the bogies (under carriages) as is done in Russia- China borders. Russia uses 1520 mm whereas China has Standard gauge. Changing bogies take a lot of time, hence the VGA. Here the train goes through a specially designed gauge change mechanism where the wheels get unlocked and pushed-in or out as the case may be and the wheels are locked in new position (all automatically) while travelling on a tapered track slowly and the train continues its journey non-stop.
In India we can use this for future trains that may travel both on hi-speed track and the regular desi tracks. For instance IR plans a hi-speed track from Mumbai to Ahmadabad...beyond that we have regular BG track. Mumbai Rajadhani can run on this track upto Baroda on hi-speed SG and switch to BG route for its onward travel to Delhi without having to change trains. You can have common rolling stock thus saving on inventory & capital investments.
See video ... click here