 The standard speed limit for cars on Irish motorways is 120 km/h (with a minimum speed limit for any type of vehicle of 50 km/h - 31 mph).The standard speed limit on national roads is 100 km/h (62 mph).A number of local authorities have passed special speed limit by-laws permitting dual carriageways in their administrative area to carry motorway speed limits of 120 km/h (75 mph).