Trains on the other hand can be stalled for any number of reasons including technical incompatibility, a lack of people on the ground or determination to smooth the way, or the unwillingness of railways and politicians to cooperate.

While a lot has been done to resolve the historical barriers to crossing borders by rail, particularly regarding track gauge with the successful introduction of gauge-changeable wheelsets, the increasing complexity of modern trains and signalling systems, aggravated by ever more onerous rolling stock certification processes in neighbouring countries coupled in some cases with a growing unwillingness to cooperate, are creating new barriers. The noticeable trend towards the withdrawal of international passenger services is especially worrying.

While some railways are retreating behind their national borders, the world is becoming increasingly international fuelled by growing trade between countries and the insatiable desire of people to travel.

The prize could be huge if only train operators would take the trouble to find solutions to cross-border barriers, especially as many are self-inflicted.

Here are two observations to ponder. Rail carries a tiny proportion of the vast amount of freight traffic moving between Asia and Europe despite offering much shorter transit times which would be particularly attractive to high-value freight which could afford to pay the higher rates by rail. This is because rail fails to organise and market itself effectively as a single operation and service quality is often poor.

The steady growth which French National Railways' (SNCF) domestic high-speed services have enjoyed since 1981 has stalled thanks to the economic recession. Conversely, SNCF says its international high-speed services are continuing to grow, demonstrating that there is a market for them.

Eurostar is continuing to increase its revenue, but the fact that all Eurostar passengers are required to negotiate airport-style security checks is one of the many quirks of trying to operate trains through the Channel Tunnel along with outdated rules which continue to prevent other types of passenger train and locomotives from using it.

The continuing failure to challenge such restrictions results in the scandalous underuse of hugely-expensive infrastructure assets.

Technology should be our servant and not our master, but all too often the reverse is true. Take the current situation between Belgium and Luxembourg where SNCB trains from Brussels are being terminated at the border because Luxembourg has not yet approved Belgium's new TBL1+ safety system. A dispute regarding cross-border acceptance of trains is preventing the introduction of high-speed services between Barcelona and French cities on the new Barcelona - Perpignan line, with passengers being forced to change trains unnecessarily at Figueres. The collapse of the Brussels - Amsterdam service due to the withdrawal of the problematic Fyra high-speed train fleet continues without a solution in sight. Such failures put rail in a very poor light and jeopardise its ability to gain support for future projects.

The trend for national railways to set up shop and invest in new start-ups or acquisitions in neighbouring countries has benefits and drawbacks. On the one hand, German Rail's increasing dominance of the European railfreight market is allowing it to launch new cross-border services such as between Poland and Britain. On the other hand, SNCF's decision to invest in Italy's open-access high-speed operator, NTV, appears to have affected relations between SNCF and Italian incumbent Trenitalia, a consequence of which is that there are no longer any through passenger trains along the Mediterranean coast with passengers forced to change trains on the French-Italian border at Ventimiglia.

Buses have replaced trains on some routes such as Vienna - Italy and between Nuremberg and Prague during the day. SNCF's solution to the absence of trains across the border at Ventimiglia is the introduction of buses between Marseille, Nice, Genoa and Milan through its new iDBus subsidiary. If railways continue to substitute trains with buses, this will severely undermine the viability of cross-border lines leading to inevitable closure.

Perhaps the time has come to develop international passenger corridors in Europe along the lines of the freight corridors now coming into operation. A corridor-based approach to managing cross-border routes would put the spotlight on operational weaknesses, develop solutions, and find operators willing to run commercially-competitive services. Without such an initiative the prospects for many international passenger services look bleak.