It applies only to cities connected by direct train service running “several times a day” and enabling travelers to spend a minimum of eight hours at their destination.

It does not apply to connecting flights, and it carves out an exception for the Paris Roissy-Charles de Gaulle Airport, one of Europe’s busiest passenger hubs, so that air routes between Charles de Gaulle and other French cities will stand.

Finally, since a significant amount of the nation’s high-speed train traffic is routed through Paris, only a limited number of cities away from the capital have direct train service between each other that would satisfy the rules in the decree.

When all is said and done, only three routes are actually cut — those between Paris-Orly Airport and the cities of Nantes, Bordeaux and Lyon.

The exceptions are meant to ensure that train service between two cities is sufficiently robust before flights between those same destinations are outlawed. But for critics, the confusing jumble of conditions has made the measure largely toothless.