Security was stepped-up following the Thalys incident when passengers overwhelmed an armed terrorist travelling on the train, with patrols by armed police at stations and baggage checks. The Paris attack will no doubt lead to more security measures.

The future of the Schengen area of 24 European countries where border controls have been eliminated is already under threat as countries struggle to cope with the massive movement of refugees and migrants from the Middle East and Africa across Europe. Border controls have been temporarily reintroduced in Finland, Sweden, Germany, Austria, Slovakia, and since November 13, in France, while cross-border rail services have been disrupted between Germany, Austria, and Hungary.

At the very least we could start to see the reintroduction of on-train passport control as used to take place between many countries prior to the introduction of the Schengen agreement in 1995. While this would be costly, it would be the least disruptive to both railways and their passengers of a range of potential security measures.

The sight of armed police at airports and major railway stations has become common place in Britain since the 2007 terrorist attack in London. Litter bins were removed and left-luggage offices were closed temporarily. Such measures will surely be introduced at major stations elsewhere in Europe.

Going beyond this would be extremely problematic for railways. At present, only Eurostar operates full airport-style security checks and passport controls before passengers are allowed to board trains. This has made it very difficult to expand Eurostar services outside a small network because of the prohibitive cost and difficulty of providing such facilities at stations. Indeed, passengers returning to London on the service from Marseille have to leave the train at Lille to pass through security and immigration which adds 1h 15min to the journey.

Following the Madrid commuter train attacks, Renfe introduced baggage scanners at stations for long-distance services but passengers and their hand baggage are not screened, and Renfe shied away from introducing security checks for commuter services because of the large number of people and stations involved, and the massive disruption it would cause.

Any proposals by national security agencies to introduce airport-style security checks at stations for cross-border train services should be resisted by railways for several reasons. First, it will take time to create secure areas at stations and to purchase and install the equipment and hire and train staff. Platforms will have to be dedicated to international services so that they can be made secure, which will have implications for station capacity and train operations.

Railways operate very differently from airlines. Aircraft mainly fly point-to-point whereas very few passenger trains operate non-stop. Take Thalys for example, only seven of the 23 trains per weekday operating between Brussels and Paris are non-stop services between the two capitals. All the remaining trains originate in either Amsterdam or Germany. While it might be possible to create a secure area for Thalys at Amsterdam Central and Rotterdam Central, as these are large stations, it would be extremely difficult to do so at Amsterdam Schiphol Airport and Antwerp Central as both these stations have underground platforms which are used by numerous domestic trains. Withdrawing stops at Schiphol and Antwerp would be a serious financial blow to Thalys.

Indeed, widespread introduction of airport-style security would be extremely costly and is likely to result in the removal of intermediate stops or the withdrawal of entire services. Many cross-border services have already been withdrawn because of the perceived difficulty of operating them or because railways have lost interest in such services.

Cross-border services are also used by passengers travelling domestically, but this is likely to be forbidden or restricted severely as already happens with Eurostar. Barring passengers from travelling domestically would jeopardise the economics of operating cross-border services. A solution would be to conduct the security and passport checks at the border, but passengers would have to disembark to do this which would extend journey times and make such services far less attractive.

A further reduction or curtailing of cross-border services would also be a serious setback for the European Union and its desire to create a single market for rail. It would undermine many of the objectives of the Fourth Railway Package, part of which is expected to become law next year. There is little point in trying to remove the technical obstacles to international rail operations if the services have been withdrawn anyway.

A far better solution would be to step up covert monitoring of passengers at stations and on trains using intelligence gathered on suspected terrorists. As discussions over how to respond to the security threat posed by terrorists intensify, we must find intelligent solutions to defeat terrorism and not resort to measures which will destroy a key element of rail travel in Europe.