Trunk roads in Ireland

In 1977 the classification was changed to national primary and secondary, regional, and local roads.

Typically, each segment previously classified as trunk or link respectively became national or regional, but the numbering was done on a new basis.

In addition, Esso road-maps of Ireland from the 1950s show the Trunk and Link road network.

This current system of road classification and numbering has its origins in the late 1960s: the Minister for Local Government, Kevin Boland, announced on 23 July 1969 that a national road network would be formed, to be planned and funded by central rather than local government.

Sections of national roads upgraded to motorway status would use letter M instead of N in the identifier (beginning in 1983).

The first nine Trunk Roads (T1, T2, T3, T4, T4a, T5, T6, T7, T8) radiated out from Dublin (with the T8 branching off the T7 at Enniscorthy) and followed an anti-clockwise pattern.

Confusingly, some old road signs still show the former (now obsolete) Trunk and Link road-numbers.

A notable feature of the former system was multiplexing (or concurrency), where a section of road was designated by two or more route numbers.

The road between Cavan, Butlersbridge, Cloverhill and the border with Northern Ireland (near Wattle Bridge in County Fermanagh) was a triple multiplex of the T10, T15 and T35 routes.