A MAINLINE train station in France at the end of summer hums with the thrill of journeys taken and families reunited. The French travel more by high-speed rail than any other European nation. Trains in the French mind are about more than just efficiency and convenience: they are a symbol of national prowess. Which is why the thwarted attack on August 21st on a high-speed train bound for Paris has stirred up a particularly difficult debate.

The attempted assault took place when Ayoub El Khazzani, a 25-year-old Moroccan-born man, emerged from an on-board lavatory shirtless and armed with an automatic rifle, nine clips of bullets, a hand gun and a box-cutter. Thanks to the fortuitous presence and quick thinking of two off-duty American servicemen, who together with other passengers overpowered him, nobody was killed. François Hollande, the French president, said that the assault would otherwise have “degenerated into carnage”. He awarded the Légion d’honneur, the country’s highest honour, to six of those who intervened.

The French public prosecutor, François Molins, has opened a formal investigation into attempted murder in connection with a terrorist act. Mr El Khazzani claimed that he found the weapons in a park in Brussels, the Belgian capital, where he boarded the train, and that he meant only to rob passengers, not kill them. Mr Molins says he is a radical Islamist whose planned assault was “well targeted and premeditated”. Shortly before loading his weapon, Mr Molins said, Mr Khazzani watched a jihadist video on his phone. He had recently returned from Turkey, a country often used by would-be jihadists as a route to Syria.

That the gunman was able to board a train with a bag loaded with heavy weaponry is not surprising. There are no security checks inside the EU’s passport-free (or Schengen) zone. To board a Eurostar train from Paris to London, outside the Schengen area, requires lengthy baggage and passport checks. Not so when boarding a high-speed train—on a neighbouring but segregated platform of the same Paris station—to Belgium or the Netherlands.

Improving security without compromising convenience is tricky. Ever since deadly terrorist attacks in Paris eight months ago, French soldiers have patrolled stations, though not trains. European transport ministers will discuss how to improve security in October. Ségolène Royal, France’s ecology and transport minister, has called for metal detectors for railway travel, especially for trains that cross intra-EU borders. But this is highly unlikely. Guillaume Pépy, the head of the French railways, dismisses the idea of airport-style security on trains as unrealistic. There is 20 times more passenger traffic on trains than on planes in France. It is precisely the ease and efficiency of train travel that makes it such a cherished part of French life.