>>1032615>>1017944The TALGO gauge change system (btw Iberian is 1668, 1524 I think is russian gauge) was introduced in the 1960's to allow through trains from Spain to France and from there on to other standard gauge countries. Originally the cars formed a fixed unit called a branch, and the locomotive would be uncoupled and push the branch through the gauge changing mechanism. The branch would then be picked up by a french locomotive which would pull it from there on. This whole thing took no longer than 30 minutes or so.
Nowadays this system isn't used anymore for international trains, since Spain has discontinued all non-HSR international trains, except the ones to portugal which has iberian gauge and also except regional trains which end just across the border but using iberian gauge tracks all the way.
Instead it is used for trains running on both HSR and conventional tracks, and it is used quite frequently since the terrible design of Spain's HSR network has it function exclusively on a radial pattern with Madrid at the center, while passenger demand to and from Madrid isn't always in highest demand, and the itineraries with most demand consequently don't have HSR for but part of their length. For example all trains which run from Barcelona toward the north of the peninsula (Burgos, Bilbao, Santander, Asturias, Galicia) run on HSR tracks until Lleida or Zaragoza, and there will change gauges and continue along on conventional iberian gauge tracks.
Trains that use this system don't have proper axles, instead they use the TALGO system developed in the 1940's where the carriages "hang" from "pillars" over each wheel, thereby making axles unnecessary while maintaining stability through a very low center of gravity. The lack of axles allows for this easy gauge change. This system was adapted to a passive tilting system in the 1980's, which allowed trains to run at 160km/h on lines designed for 140km/h.
Ask away if you have any more questions.
