Paris: Since 9/11, airports around the world have implemented tougher security checks for travellers, but the foiled attack on a packed high-speed train in Europe raises questions about whether railway stations should follow suit.

The suspected gunman, named as 25-year-old Moroccan national Ayob Al Khazzani, boarded the Amsterdam-Paris express in Brussels on Friday with a Kalashnikov assault rifle, a Luger automatic pistol, nine cartridge clips and a box-cutter, investigators say.

Courageous intervention by a trio of young Americans who overwhelmed the attacker prevented a possible massacre.

In the wake of the episode, Belgium said it would increase baggage checks and patrols on high-speed trains.

And France said its state-run rail firm, the SNCF, would introduce an emergency hotline to report “abnormal situations”.

Experts say these are valuable tools in the fight against terrorism.

But at the same time, these fast-track measures also highlight an underlying problem: applying airport-style security to railway stations is almost impossible.

“The idea of extending the airport system to railway stations today isn’t something that I can call realistic,” SNCF head Guillaume Pepy, said.

“There’s a choice — you either have comprehensive security or low [transport] efficiency.”

Railway hubs were built in the 19th and 20th centuries when today’s type of terror threats was inconceivable.

As a result, main stations are designed to have a maximum free flow of people on and off trains, with sometimes dozens of departures or arrivals at peak times.

They are served by a network of smaller stations — 3,000 of them in France alone.

“Aeroplanes leave from a specific place — you can build a security apparatus around it,” Raffaello Pantucci of the Royal United Services Institute in London said.

“It’s just not possible to do that with trains. You would have to do that at every station.”

Retrofitting the railway network — nationally and internationally — so that it meets airport-style criteria would be astronomically costly, Marc Ivaldi at the IDEI research institute in Toulouse, southwestern France, said.

“The task is strictly impossible in the immediate future,” he said.

In the absence of regular station screening, watchdogs have to rely on high-visibility patrols, spot checks, enrolling the public in campaigns for greater vigilance, installing video surveillance cameras and beefing up coordination between police and railway security.

The notable exception in Europe for security screening is the cross-Channel Eurostar service, which connects Britain to France and Belgium.

It requires passengers to arrive at a purpose-build terminal around a half-hour before their train departs and subjects them to pre-departure baggage and ID checks.

But this is largely due to Britain not being part of the joint Schengen passport-free zone, as well as security measures required for travel through the Channel Tunnel.

The baggage screening, too, is less demanding than at airports. Items are X-rayed, but liquids are not confiscated.

“The key need is to secure the Thalys and a certain number of high-speed trains,” said Ivaldi, referring to the service, on which Friday’s attack occurred.

In Italy, passengers departing from some major stations have since May 1 been subject to security checks before boarding.

Railway security has been tightened too, in Spain.

Coordinated bomb attacks on Madrid’s commuter rail network on March 11, 2004, left 191 dead and 1,800 injured, in the deadliest terror attack in Spain’s recent history.

Today, passengers boarding long-distance trains have their luggage checked.