The Carreteras Nacionales de España or National Roads of Spain are roads of governmental property, managed by the Ministry of Fomento and conform the Red de Carreteras del Estado or State Roads Network. The road numbering scheme is normalized according to the rules set by the fourth Plan General de Carreteras (General Road plan) of 1939-1941 (Plan Peña). The territory (without the Canary Islands and Balearic Islands) is divided into 6 radial sectors, whose boundaries are the radial roads that link Madrid to the coasts and borders. These radial roads follow a clockwise system:
N-I (From Madrid to France via Irún or Carretera de Burgos): Northbound
N-II (From Madrid to France via La Jonquera or Carretera de Barcelona): North-eastbound
N-III (From Madrid to Valencia or Carretera de Valencia): Eastbound
N-IV (From Madrid to Cádiz or Carretera de Andalucía): Southbound
N-V (From Madrid to the Portuguese border or Carretera de Extremadura): Westbound
N-VI (From Madrid to A Coruña or Carretera de A Coruña): North-westbound.
Now, these roads have been upgraded to Autovías, changing their names to its geographical heading instead of using the city they link to Madrid, and not varying their number (A-1, A-2,...). The codes for the national roads consist of 3 numbers (e.g.: N-XXX, where X is a number) assigned as follows:
The first one is the number of the sector where the road starts: those roads starting between N-I and N-II are numbered N-1XX; those between N-II and N-III, N-2XX…
The second is the distance in hundreds of kilometers of the beginning in a straight line from the Puerta del Sol, in Madrid. Thus, if the road starts less than 100 km away the road will have number 0; 1 if born between 100 and 200 km away from Madrid, and so on.
The third one is assigned regarding its direction: if the road has a radial shape (from Madrid), it will be an odd number; if it is a transversal road (not leading to Madrid), it will be assigned an even number (0 is included).
If the road is radial, the beginning will be the closest end to Madrid. However, if it is a transversal road, it will start in the end that makes an anti-clockwise direction. Example:
The road that links Cordoba and Tarragona via Cuenca is not a radial road. It starts in Córdoba so that the direction is anti-clockwise (from the South to the North-East). Córdoba is between N-IV and N-V, and Córdoba is 295 km away from Madrid, so the two first numbers will be N-42X. The third number has to be an even number, which in this case is 0. So the road from Córdoba to Tarragona via Cuenca is the N-420.
The road that links Madrid and Ciudad Real via Toledo diverts from N-IV (N-4XX) in Madrid (N-X0X), and it’s a radial road (odd number). Consequently, its code is N-401.
Some exceptions may exist if the road is within Basque Country or Navarra limits, where other numbering scheme applies (e.g.: N-102)
