digits, it is road owned by a regional government, usually Andalusia or Aragon, and may or may not be a divided highway. AP stands for "autopista de peaje" (toll motorway) N stands for "nacional" (national), single carriageway road owned by the national Government. National roads 1 to 6 are radial roads linking Madrid with major cities or borders with France and Portugal. All other roads are numbered with three digits. Other letters refer to the code of the region or city that is served by the road. See for example M-30, with M standing for Madrid. Turkey O, D, I system O stands for "Otoyol" (motorway) D stands for "Devlet Yolu" (expressways/major highways) I stands for "Il Yolu" (provincial roads/minor highways) Vietnamese QL, TL, HL system The following abbreviations appear on guide signs and kilometer posts: CT (expressway) QL (national road) TL or ĐT or (provincial road) HL or (rural district road) ĐCK (canal towpath) See also Highway shield Highway location marker Driver location signs Asian Highway Network Auxiliary route (United States) China road numbering International E-road network (Europe) State-numbered route (countries that are divided into states) Numbered street List of roads and highways Notes References Further reading Road numbering systems, covering most nations Explanation of British road numbers Roads French inventions Identifiers