Some countries such as the Netherlands have modified their track gauge, but in Spain it is still used, except on high-speed lines, where the European international track gauge of 1435 mm is used, as opposed to the Iberian gauge of 1668 mm.

The "European" or Standard Gauge in Spain is 1,435 mm (4 ft 8.5 in), which is the global standard used across most of Europe, North America, and China. However, Spain is unique because it uses two distinct gauges for its national rail network. The older, traditional network (managed by Adif) uses the Iberian Gauge of 1,668 mm, which is significantly wider than the European standard. This was originally implemented in the 19th century for technical and defense reasons. Since 1992, starting with the Madrid-Seville line, all of Spain's high-speed AVE lines have been built using the 1,435 mm Standard Gauge to allow for seamless, high-speed connections with the rest of Europe via France. To bridge the gap between the two systems, Spain uses sophisticated "gauge-changer" facilities where specialized trains like the Talgo can adjust their wheelsets while moving at low speeds, allowing them to transition between the broad-gauge local lines and the standard-gauge high-speed tracks.