The R173 road is a regional road

Regional road

A regional road in Ireland is a class of road not forming a major route , but nevertheless forming a link in the national route network. There are over 11,600 kilometres of regional roads. Regional roads are numbered with three digit route numbers, prefixed by "R" A regional road in Ireland is a...

 in Ireland

Republic of Ireland

Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...

, running its full length in County Louth

County Louth

County Louth is a county of Ireland. It is part of the Border Region and is also located in the province of Leinster. It is named after the town of Louth. Louth County Council is the local authority for the county...

. It loops around Cooley Peninsula

Cooley peninsula

The Cooley Peninsula is a hilly peninsula in County Louth, Ireland, which includes towns such as Omeath, Carlingford and Greenore.-Geography:...

, mainly along the coast. It nearly encircles the Cooley Mountains

Cooley Mountains

The Cooley Mountains are located on the Cooley Peninsula in northeast County Louth in Ireland. They consist of two ridges oriented northwest to southeast, separated by the valley of Glenmore with the Big River running through it....

.

It starts at a roundabout at Ballymascanlan, just north of Dundalk

Dundalk

Dundalk is the county town of County Louth in Ireland. It is situated where the Castletown River flows into Dundalk Bay. The town is close to the border with Northern Ireland and equi-distant from Dublin and Belfast. The town's name, which was historically written as Dundalgan, has associations...

, where it meets the N52 and the M1/N1 roads.
It then heads east, along the northern coast of Dundalk Bay to The Bush where it veers north, past the village of Grange to Carlingford

Carlingford, County Louth

Carlingford is a coastal town and townland in northern County Louth, Ireland. It is situated between Carlingford Lough and Slieve Foy, sometimes known as Carlingford Mountain...

.
From there it heads NW along the southern shore of Carlingford Lough

Carlingford Lough

Carlingford Lough is a glacial fjord or sea inlet that forms part of the border between Northern Ireland to the north and the Republic of Ireland to the south. On its northern shore is County Down and on its southern shore is County Louth...

, through the village of Omeath

Omeath

Omeath is a village on the R173 regional road in County Louth, Ireland, close to the border with Northern Ireland. It is roughly mid way between Dublin and Belfast, very near the County Louth and County Armagh / County Down border. Omeath has a population of 439, and is approximately from...

 to the Northern Ireland

Northern Ireland

Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...

 border where it becomes the B79 into Newry

Newry

Newry is a city in Northern Ireland. The River Clanrye, which runs through the city, formed the historic border between County Armagh and County Down. It is from Belfast and from Dublin. Newry had a population of 27,433 at the 2001 Census, while Newry and Mourne Council Area had a population...

, County Down

County Down

-Cities:*Belfast *Newry -Large towns:*Dundonald*Newtownards*Bangor-Medium towns:...

.

The R173 is a former Trunk Road

Trunk Roads in Ireland

Ireland has an extensive network of public roads which connect all parts of the country with each other. Roads in Ireland are currently classified as motorways, National Primary routes, National secondary routes, Regional roads and Local roads. The introduction of this classification system began...

and was previously numbered as the T62.

The road is 32 km (19.9 mi) long.