The Department of Transport has upgraded around 100kms of dual carriageway around the country to motorway status.
The redesignation affects sections of the N6, N7, N8 and N9.
A speed limit of 120kph will apply on the reclassified routes and learner drivers will no longer be able to use the use the roads.
Transport Minister Noel Dempsey says the move is intended to enhance safety on the routes and to shorten journey times.