Under the Local Government (Roads and Motorways) Act (Declaration of National Roads) Order 1977 - which defined the original national primary and secondary routes - the N5's terminus was set at Castlebar. The section of road between Castlebar and Westport was designated part of the N60 road, a national secondary route. Outdated road signage (which should have been replaced by the local authority or at least corrected) in Castlebar also indicates that the N5 commences on the Castlebar inner relief road at the Westport Road roundabout.

However the road between Westport and Castlebar was upgraded to national primary route status in 1994 (under the Roads Act, 1993 (Declaration of National Roads) Order, 1994) and became part of the N5 road. Road signage on this route reflects this. The route no longer runs through Castlebar town centre in any case, having been bypassed by a relief road. Road signage on the N4 road in Dublin was mostly patched to reflect the new destination only in the early 2000s but some signs reading Castlebar still remain.

• http://en.wikipedia.org/wiki/N5_road#Confusion_over_termination_point