Pau–Canfranc railway

The legal title to build the Pau to Oloron-Sainte-Marie section was given to the Chemins de fer du Midi, on signing of a memorandum between the company and the Minister of Agriculture, Trade and Public Works on 10 August 1868. The agreement was approved by an imperial decree on the same date, and declared a public utility and definitively granted by a law on 23 March 1874. After completing construction, this section came into operation in 1883.

On 17 July 1879 a law was passed (the Freycinet plan), covering 181 ranking railway lines of general interest. No.178 was a line from "Oloron in Bedous (Lower Pyrenees)", and further a line from "Oloron to Puyoô in Saint-Palais, by the Gave Oloron Valley". Subsequently, on 17 July 1886 No.179 was legally titled to the Chemins de fer du Midi by a separate law. The Oloron to Bedous section was declared a public utility, with the concession confirmed on 27 June 1897; the latter proposed section to Puyoô was never built, cancelled by a law on 8 July 1900.

The international section from Bedous into Spain, was the subject of an international convention between France and Spain signed on 18 August 1904. Approved by a French law on 10 January 1907 and promulgated by a decree on 6 February 1907, the concession to build was granted to the Chemins de fer du Midi after an agreement with the Minister of Public Works was signed on 20 June 1907, and declared a public utility by a law 2 August 1907.

The Franco-Spanish convention was amended by a protocol signed on 15 April 1908, which provided that the required Somport tunnel would be equipped with a 1,435 mm (4 ft 8 ¹⁄₂ in) track, and that the Spanish government would fund a suitable interchange station on their border. The protocol was enacted by a decree on 25 January 1909.

Construction of the Somport tunnel was inaugurated on 12 July 1912, and after delays in its construction due to World War I, completed in 1915. Spanish project engineer Ramírez de Dampierre began construction of the Canfranc International Railway Station in 1923, and it was formally opened on 18 July 1928, in the presence of King Alfonso XIII of Spain and the president of the French Republic Gaston Doumergue.

On full opening, the line converted immediately to overhead line electrification at 1500 V DC. The line is built to 1,435 mm (4 ft 8 ¹⁄₂ in), but on connecting to the Iberian gauge at Canfranc, the enlarged station there allows for suitable interchange facilities.

From Pau, the line follows the Gave d'Aspe valley, reaching Bedous (altitude 405 metres (1,329 ft)) in a relatively flat terrain. After this it climbs into the Pyrénées Mountains, with an average gradient of 25 mm/m (0.30 in/ft) (2.5 %) to Etsaut, and then 43 mm/m (0.52 in/ft) (4.3 %) to the tunnel at Somport, where the line reaches its maximum altitude of 1,211 metres (3,973 ft). To reach this point from Bedous, the steeply climbing line traverses both sharp curves, and passes through 14 tunnels including the helical tunnel at Forges-d'Abel.

Due to the Franco-Spanish international convention under which it was built, the Somport tunnel and quasi-French control of the French-side of Canfranc international railway station continued during World War II. The Spanish authorities came to an operational agreement with the German Nazi Wehrmacht authorities, whereby passenger train services continued, with freight-trains carrying mined Tungsten north, and French grain plus trans-shipped Swiss gold south.

The Pau-Oloron-Sainte-Marie section during renovation, 2010

In September 2008, the major electrical substation which supplied power on the Pau to Oloron-Sainte-Marie section was turned off and removed, to permit the commercial expansion of an industrial estate. In September 2010, the line was closed for six months to allow major works to be undertaken, both to the infrastructure and environment. The entire line infrastructure, including all ballast and the redundant Midi-catenary, was removed, the roadways cleared and new drainage built. Then new ballast and lines were installed, laid out to allow later possible electrification. Finally, TER Aquitaine replaced the previously used SNCF Class X 2200 railcar units with modern SNCF Class X 73500.

Since the mid-2000s, the Aquitaine region has supported the lines reopening. On 15 March 2013 Alain Rousset (President of the Aquitaine region) and Luisa Fernanda Rudi Ubeda (President of the Government of Aragon) signed a Memorandum of Understanding, for a plan of cross-border cooperation up until 2020. The memorandum sets a timetable for reopening of the line in two phases, the Oloron section Bedous in 2015, then Bedous section of Canfranc in 2020. Subsequently, the Autonomous Community of Aragon acquired Canfranc station from RENFE, with a plan to restore and develop it as a catalyst (tourism, academic, economic) for the region.

After signing the memorandum, the Aquitaine Regional Council (ARC) commissioned SNCF to undertake preliminary studies on opening the 25 kilometres (16 mi) section from Oloron-Sainte-Marie to Bedous, and to survey the whole line to Canfranc. The study found that all tunnels on the line were in good condition, except for the sidewall of Peilhou tunnel that had collapsed. Similarly, the bridges are still in place, except south of Bedous towards Canfranc there are three major areas of work required:

• Estanguet bridge, destroyed by the 1970 accident
• Bigue bridge over the river Aspe, south of Accous. The bridge was destroyed by a flood on 5 October 1992. Since then the building of the RN 134 bypass road from Bedous and Accous (6.5 kilometres (4.0 mi), which cost EUR 41.66 million) has also removed the approach infrastructure
• Peilhou and Serbers viaducts. During the construction of the RN 134, retaining the viaducts would have created too sharp a curve on the road. Resultantly, it was agreed to keep both viaducts intact but remove one approach embankment of each viaduct, to enable the creation of a wider road.

Despite an unfavorable opinion from both the public enquiry and the Commission of Inquiry, ARC declared the project a public utility by the signing of the decree 19 February 2014.

SNCF were commissioned by ARC to undertake full costings and present a project plan for the reopening of the Oloron-Sainte-Marie to Bedous section. The SNCF reported that substantial work was required, including the replacement of 12 bridge decks, rebuilding of all road crossings to modern unmanned standards, and full renovation of all stations. Further, SNCF stated the requirement of modern landslide protection along the line. The ARC announced that the project was valued Eur122M, with Eur100M coming from ARC's budget and a minimum of Eur30M coming from other sources, mainly the French government and EU grants.

Following delays in agreement on budget funding, SNCF did begin work on 26 September 2014 with a projected opening to Bedous by March 2016. In a replication of the project to renovate the Pau to Oloron-Sainte-Marie section, the project included: removal of all line infrastructure; renovation of all earthworks and bridges; removal of two road crossings, renovation of all other crossings to modern unmanned standards; installation of the required landslide protection and matts; and then relaying with new ballast, concrete sleepers and steel rails.

SNCF proposed installation of Automatic Block restricted permissiveness signalling between Oloron and Bedous. There will be three sections: Bidos, Lurbe-Saint-Christau and Bedous.