OVER the last 25 years Spain has made a massive effort to develop a modern standard-gauge railway network and during this period the country has gone from no high-speed lines at all to Europe's largest high-speed network. According to the UIC, Spain has the third largest network in the world, behind only Japan (2664km) and China (9356km).

The fruits of an investment worth more than €57bn (adjusted for inflation and including rolling stock) have been reaped this year with the opening of two new lines, which mark the beginning of a new phase in high-speed rail development in Spain.

In January, Renfe launched commercial services on the 131km Barcelona - Figueres high-speed line, the first standard-gauge link between Spain and the rest of Europe, which eliminated the most significant barrier to cross-border operation and ended the isolation of the Iberian rail network.

Last month the network grew again with the inauguration on June 17 of the €1.9bn Albacete - Alicante line.

Nine AVE services operate in each direction, cutting the Madrid - Alicante journey time by 50 minutes to 2h 20min, with trains calling at Cuenca, Albacete and Villena, where a new station has been constructed. Renfe is using class 100 and 112 trains, which have increased capacity over conventional services by 40% or 6300 seats per day, and the price for a full-fare tourist class ticket is €64.90.

An unusual feature of the 165km line is that it involved upgrading 65km of conventional line originally constructed between 1988 and 2006. This means the maximum commercial speed is limited to 300km/h instead of 350km/h, which is the standard for most ERTMS-equipped high-speed lines in Spain.

Despite Spain's economic difficulties, the country's romance with high-speed rail is far from complete - or so it appears. Although Spain already boasts 30% of Europe's total high-speed route mileage, Adif says that an additional 1244km are currently under construction, while 525km are still in the design phase and a studies are underway on a further 251km.

To understand the future of the high-speed network, it is necessary to look at how the system has evolved since the early 1990s. A glimpse at the railway map quickly reveals that the high-speed system echoes the conventional network constructed during the 19th and 20th centuries, largely duplicating the old system and its principal features - a radial design with Madrid at its heart, and a progression of the new infrastructure from the centre to the coastline of the Iberian Peninsula, serving the main cities of the sparsely-populated plateau along the way.

The backbone of the system runs from Seville to the French border, a diagonal axis composed of the first two new lines to be constructed. Initially conceived as a means of cutting the distance by rail between the capital and Andalucía, the 471km Madrid - Seville line morphed into Spain's first high-speed project, which completed in 1992. The 750km Madrid - Barcelona - French border line opened in phases, reaching Lleida in 2003, Tarragona in 2006, Barcelona in 2008 and Figueres this year. Two short branches connected Huesca to the high-speed network in 2003 and Toledo in 2005, while a longer branch extends 154km from Córdoba to Malaga. This route is used by Europe's longest high-speed services, which cover the 1112km between Malaga and Barcelona in 5h 45min.

In the southeast, a 397km line connects Madrid with Valencia, with a 239km branch to Albacete and Alicante which will eventually be extended south to Murcia.Spanish-HS

In the northwest the network ruptures, with just two operational sections isolated not only from each other but the rest of the high-speed system. The 180km Madrid - Valladolid line will one day form part of a high-speed link between the capital and the north, but for now it remains an operational island severed from the rest of the network. Boring was completed in 2011 on a standard-gauge tunnel between Madrid's Chamartin and Atocha stations, but together with the double-track link between Atocha and the junction of the Valencia line, it is not expected to open until 2015. Even worse, the tunnel will not allow trains to stop at Atocha until new through platforms are completed in 2020.

In Galicia, the 211km Ourense - Santiago de Compostela - A Coruña broad-gauge line was completed in 2011 and combines a new-build passenger line on its first section with an upgraded, mixed-traffic conventional line.

The lack of physical connections between corridors and the varying pace of development on lines still under construction helps to explain the existence of a fourth and final group of lines which are defined more by the impact of the economic crisis than geography. Despite allocating 35% of the total transport funding to the completion of the high-speed rail network, the 2013 budget contained a 26% reduction in infrastructure investment, and as the recession shows no signs of abating in Spain, many more cuts are expected to follow.

Adif puts the total investment already made in lines currently under construction at €12.3bn, an astonishing figure which nonetheless is insufficient to complete works now underway. The development of Spain's high-speed rail network therefore appears to be reaching a point of stagnation.

In this context, and despite maintaining that all the lines under construction across the country are of equal importance, the Spanish government clearly has one priority in mind: the Madrid - Galicia line, which branches off the Valladolid line, is expected to reach Zamora in 2014 but will not connect with Ourense, and thus close the existing Galician gap, until the end of the decade.

To lighten the financial burden on the state, contracts for the installation of the superstructure on the initial sections into Galicia have been modified to include not only the construction works but also maintenance of fixed installations such as signalling and electrification over a period of 20-30 years. Under this scheme, 40% of the contract value is paid upon completion of the works, with the remaining 60% paid thereafter in installments. The Spanish government hopes these public-private partnerships (PPP) will be more attractive to bidders.

Consideration is also being given to constructing the final section of the route as a single track line to reduce costs.

A similar situation can be found in Castile. While civil works to extend the Valladolid line towards Leon were completed months ago, the Spanish government is now slowing the rhythm of the project and is not expected to tender the superstructure contracts - also being let on a PPP basis - until the end of this year. North of Leon, the 25km Pajares Base Tunnel between Castile and Asturias also faces problems.

The first civil works were contracted back in 2003, and its twin tubes were finally holed through in 2009. Since then, engineers have been grappling with structural issues, including water leaking continuously at a rate of 300 litres per second towards the north portal. With more than €3bn already invested, Adif has still to confirm a completion date for this mixed-traffic line, which is built for dual-gauge operation.

Meanwhile, construction has been suspended completely on the Valladolid - Burgos high-speed line, and substantially slowed down on the Basque Y, which will link Vitoria, Bilbao, and San Sebastian with the French border crossing at Irun/ Hendaye. Plans to link both lines and connect them to the Madrid - Barcelona line have been dropped. Likewise, proposals for a new line between Almeria and Murcia have also been shelved.

Finally on the Madrid - Lisbon corridor, an isolated section of new line between a remote area of central Extremadura and the Portuguese border, where construction is almost complete, will open no earlier than 2015 and even then catenary will not be installed. This stretch, which has fallen victim to the abandonment of the Portuguese high-speed project, looks set to remain isolated from the rest of the high-speed network for many years.

As the completion of new lines stalls, and while planners come to terms with the fact that two incompatible national rail networks will have to coexist for decades, investment in interoperable systems made over the last 10 years are at least beginning to pay off. No less than 117 of Renfe's 246 high-speed trains are dual voltage (25kV ac/3kV dc) and are fitted with variable gauge equipment manufactured either by Talgo or CAF.

In its quest for domestic interoperability, Renfe has even converted 15 of the multi-system trains to bi-mode (diesel/electric) configuration, capable of running at 250km/h on electrified high-speed lines and operating independently over non-electrified lines. There are currently 11 automatic gauge changing facilities situated at strategic locations around the network, and these have rendered the once-challenging break-of-gauge an operational insignificance.

Dual-gauge tracks are also extending the reach of standard-gauge rolling stock. Around Barcelona and Girona existing lines have been converted to dual-gauge operation to allow standard-gauge freight trains to access the port of Barcelona. Adif is now planning to extend the dual-gauge corridor south along the Mediterranean coast to Tarragona and Valencia, and is also looking at the feasibility of converting other lines across the northern half of the country as a less costly option for linking isolated sections of high-speed line into the broader network.

With a flamboyant and interoperable (albeit incomplete) system in place, planners are now studying how to increase high-speed traffic beyond the current 6 billion passenger-km per year.

The government has announced a partial opening of the high-speed market as part of its wider programme of railway liberalisation, and Renfe will be required to lease up to 26 trains to competitors in an effort to attract new entrants.

Last February, Renfe also adopted a commercial policy more focused on yield management principles and an 11% average cut in AVE fares in February has been rewarded with a 14% year-on-year increase in ridership. It has also boosted the average load factor, a development which demonstrates that there is still some room for improvement.

Sadly however lower fares or economic recovery are unlikely to create demand in sparsely-populated areas, nor will they alter the fundamental cause behind the network's uniqueness - the uneven rate of development between corridors.