LONG lines of lorries once blotted the chocolate-box alpine landscape of the Brenner Pass, an important road link between southern and northern Europe. The Schengen agreement, which came into effect in 1995 and has now abolished border controls between 26 European countries, kept those lorries moving. But where trucks go, so do refugees. To stem the flow Austria, Denmark, France, Germany, Norway and Sweden have temporarily reintroduced controls. Others have increased spot checks in border regions.

Open borders ease the flow of exports as well as individuals. Every year people make 1.3 billion crossings of the EU’s internal borders along with 57m trucks carrying €2.8 trillion ($3.7 trillion) of goods. As well as speeding the passage of Greek olives and German dishwashers, borderless travel allows hotels in the east of Germany to have their sheets cleaned in Poland, where wages are lower, and workers in Italy to commute to Switzerland (also in Schengen though not in the EU), where wages are higher.

Reintroducing controls such as checking passports and searching lorries is mostly an irritation, though the costs are mounting. A strategy unit of the French government estimates that in the short term border checks within Schengen would cost France €1 billion-2 billion a year by disrupting tourism, cross-border workers and trade. If Schengen collapses the economic consequences would be more serious, it says: curtailing the free passage of goods permanently would amount to a 3% tax on trade within Schengen. The overall effect of hampering cross-border activity would reduce output in the Schengen area by 0.8%, or €110 billion, over the next decade.

Not only will money have to be found to patrol long-abandoned frontiers. Around 1.7m Europeans cross a border to get to work and in some regions as much as a third of the workforce makes this trip daily. Malmo in Sweden and Copenhagen, the Danish capital, have in effect become one big city. Border controls at the bridge that connects them add around 30 minutes each way. A nuisance could become a deterrent to cross-border employment, reducing job opportunities and the pool of labour employers can draw upon.