In Ireland, the highest category of road is a motorway (mótarbhealach, plural: mótarbhealaí), indicated by the prefix M followed by a one- or two-digit number (the number of the national route of which each motorway forms a part). The motorway network predominantly consists of two-lane dual carriageways and is primarily focused upon Dublin, although there are a few three-lane motorways and the M50 has four lanes at some points.