The island of Ireland, comprising Northern Ireland and the Republic of Ireland, has an extensive network of tens of thousands of kilometres of public roads, usually surfaced. These roads have been developed and modernised over centuries, from trackways suitable only for walkers and horses, to surfaced roads including modern motorways. Northern Ireland has had motorways since 1962, and has a well-developed network of primary, secondary and local routes. Historically, the road network in the Republic of Ireland was less well developed and maintained. However, with the advent of the Celtic Tiger and significant European Union funding, most national roads in the Republic continue to be upgraded. In the 1990s the Republic went from having only a few short sections of motorway to constructing motorways, dual-carriageways and other improvements on most major routes as part of a National Development Plan. Road construction in Northern Ireland has proceeded at a slower pace in recent years, although a number of important bypasses and upgrades to dual carriageway have recently been completed or are about to begin.