The R173 is a circuitous road in County Louth, running from the M1 J18 near Dundalk and going around the Cooley peninsula. It can be thought of in three sections:
- initially heading generally east from the M1 towards Greenore;
- a northbound section bypassing Greenore itself;
- a final section running northwestward along Carlingford Lough to the border.
The R173 at Ballymascanlon
The R173 from the M1 to The Bush and its continuation as the R174 provides the main route to the port at Greenore and caters for a significant amount of HGV traffic. This route is largely improved, with many sections of the road having hard shoulders and a 100 km/h speed limit.
The first section from the M1 is high quality S2, 2.5 km to Ballymascanlon (supposedly Ireland's smallest village). The 1990s bridge here replaced the old one that remains on the left of the modern route, after a high toll of traffic accidents on the old bridge and S bends approaching it. The road then loses its hard shoulders as it rejoins its historic alignment on the 2-km Bellurgan Straight, at the end of which is a short section with a 60 km/h restriction. The road regains its hard shoulders and a 100 km/h limit and after a further 2.5 km the R174 joins on the left. After a further 1.5 km the road again has a 60 km/h restriction as it passes through the village of Lordship for 1.5 km. After Lordship, the open road continues for 4 km to The Bush, bypassing some small hamlets on the way and continues as the R175.
At The Bush, the R173 makes an unsignposted TOTSO off to the left and proceeds in a northerly direction towards Carlingford. This 5.5-km section of road is largely unimproved and mostly caters to local traffic, as most others take the improved R175 and R176 instead. While the other sections of the R173 are generally close to the peninsula coastline, in this section it cuts across the peninsula and rises somewhat, providing a view of the port of Greenore and across the Lough to the Mourne mountains. In Carlingford, the R173 splits on the one way system in the narrow streets of the medieval town.
The R173 becomes the B79 at County Bridge
The section of the R173 towards Newry starts as a continuation of the R176 on the north-east of Carlingford, passing between the village and the 13th century castle on an alignment originally built for the Dundalk, Newry and Greenore railway. It then continues close to the Lough for 7 km towards Omeath. After Omeath, the road carries on north-west for 3 km in the direction of Newry to the border with Co. Armagh, where the road number changes to the B79. The proposed bridge across the estuary at Narrow Water to Warrenpoint, Co Down will link to this section of the R173.