Iberian-gauge railways is the name given to the railways using track gauge of, most extensively used by the railways of Spain and Portugal. This is the second-widest gauge in regular use anywhere in the World. The Indian gauge,, is wider. As finally established in 1955, the Iberian gauge is a compromise between the similar, but slightly different, gauges adopted as respective national standards in Spain and Portugal in the mid-19th century. The main railway networks of Spain were initially constructed to a gauge of six Castilian feet. Those of Portugal were instead built to a and later railways to a gauge of five Portuguese feet – close enough to allow interoperability with Spanish railways.
Standard gauge
Since the beginning of the 1990s new high-speed passenger lines in Spain have been built to the international standard gauge of, to allow these lines to link to the European high-speed network. Although the 22 km from Tardienta to Huesca has been reconstructed as mixed Iberic and standard gauge, in general the interface between the two gauges in Spain is dealt with by means of gauge-changing installations, which can adjust the gauge of appropriately designed wheelsets on the move. Plans exist to convert more of the Iberian-gauge network in Spain and Portugal to standard gauge, an indication of which is the use, on several stretches of recently relaid broad-gauge track, of concrete sleepers pre-drilled with additional bolt holes allowing for repositioning of one rail to adjust the track to standard gauge or the narrowing of the gauge by moving both rails closer together maintaining the perfect alignment of the loading gauge.
A commonly cited reason for the adoption of this gauge, broader than that which became the international standard, is that it was intended to hinder any use of the railroad in any of the French invasion attempts. This is possible, but the 19 January 1845 governmental decree does not state any reason, simply the gauge itself. It is known that the government entrusted such decisions to a committee, whose main work was done by civil engineers Juan Subercase and Calixto de Santa Cruz: both good civil engineers but with little experience in railroads. Their judgement, made because of their profession and lack of experience in railroads, was that since the Spanish landscape was more mountainous than that of England and France, a wider gauge would make more powerful locomotives possible, with larger boilers and, more importantly, larger fireboxes. This was obviously a miscalculation; in other areas of Spain, narrower gauges were used in the most mountainous areas, since Iberian gauge civil engineering works would have been more expensive. One example of this is the gauge FEVE.
Similar gauges and compatibility
The Indian gauge is closely similar, with only difference, and allows compatibility with the rolling stock. For example, in recent years Chile and Argentina have bought second hand Spanish/Portuguese Iberian-gauge rolling stock. 1,668 mm trains can run on 1,676 mm gauge without adaptation, but for better stability in high-speed running a replacement wheelset may be required. Backward compatibility—1,676 mm trains on 1,668 mm gauge—is possible, but no examples and data exist. Due to the somewhat narrower gauge, a strong wear of the wheels may occur if the wheelset is not replaced.
