Wikipedia
A route nationale, or simply nationale, is a trunk road in France. Trunk roads in France are important roads which cross broad portions of the French territory, as opposed to secondary or communal roads who only serve local areas.
Their use is free, except when crossing certain structures subjected to toll. They are open to all vehicles, except on certain sections having the status of motorway ( autoroute).
France currently has 30,500 km of nationales and publicly owned motorways. By comparison, routes départementales cover a total distance of 365,000 km. The main trunk road network reflects the centralising tradition of France: the majority of them leave the gates of Paris. Indeed, trunk roads begin on the parvis of Notre-Dame of Paris at Kilometre Zero. To ensure an effective road network, new roads not serving Paris were created.
Usage examples of "route nationale".
It was nearly six o'clock when the blue Alfa coasted into the town of Valence where the steel torrent of the Route Nationale Seven, the main road from Lyons to Marseilles and the highway carrying most of the traffic from Paris to the Cote d'Azur, thunders along the banks of the Rhone.
If, as he supposed, they were travelling east on the Route Nationale, which links Nimes and Avignon with Cannes and Monte Carlo, at the two former cities they would have come into the streams of refugees which for days had been heading towards the South of France.
If we took the Route Nationale from Caen, we could be in Dieppe in about three hours.
Before his rendezvous at the Hermitage he decided to take his car down the coast road and have a quick look at Le Chiffre's villa and then drive back by the inland road until it crossed the route nationale to Paris.