The R403 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,...

, linking the N4 at Lucan in County Dublin

County Dublin

County Dublin is a county in Ireland. It is part of the Dublin Region and is also located in the province of Leinster. It is named after the city of Dublin which is the capital of Ireland. County Dublin was one of the first of the parts of Ireland to be shired by King John of England following the...

 to Carbury

Carbury

Carbury , also formerly spelt "Carbery", is a village in north-west County Kildare, Ireland. It is situated in the on the R402 regional road between Enfield and Edenderry, near the border with County Offaly...

 in County Kildare

County Kildare

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

.

It starts, heading west, at a roundabout on the Leixlip Road (R148

R148 road

The R148 road is one of Ireland's regional roads which was classified following the opening of a by-passed national primary road.The section of the old N4 which has been by-passed by the M4 motorway was reclassified R148. The R148 runs from Dublin to Kinnegad in County Westmeath.The road is long...

) and crosses the M4 motorway past Weston Airport

Weston Airport

Weston Airport or Aerfort Weston in Irish, is a publicly licensed executive airport located on the R403 regional road at Leixlip, County Kildare west of Dublin, in Ireland...

 and into County Kildare

County Kildare

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

.

It follows the Dublin Road to Celbridge

Celbridge

Celbridge is a town and townland on the River Liffey in County Kildare, Ireland. It is west of Dublin. As a town within the Dublin Metropolitan Area and the Greater Dublin Area, it is located at the intersection of the R403 and R405 regional roads....

 where it crosses the River Liffey

River Liffey

The Liffey is a river in Ireland, which flows through the centre of Dublin. Its major tributaries include the River Dodder, the River Poddle and the River Camac. The river supplies much of Dublin's water, and a range of recreational opportunities.-Name:The river was previously named An Ruirthech,...

 with the R405, then heads southwest along the Clane Road to Clane

Clane

Clane is a town on the River Liffey and in the barony of Clane in County Kildare, Ireland, from Dublin.Its population of 4,968 makes it the eighth largest town in Kildare and the 78th largest in the Republic of Ireland....

.

A 10 km (6.2 mi) stretch of ruler-straight road takes it west via Prosperous

Prosperous, County Kildare

Prosperous is a village in north County Kildare, Ireland. It is within the townland of Curryhills, at the junction of the R403 and R408 regional roads, about from Dublin. Its population of 1,939 makes it the 14th largest town in County Kildare....

 to Allenwood

Allenwood

Allenwood is a small Irish village in County Kildare situated on the Grand Canal. Allenwood is located about from Dublin and half way between Rathangan and Clane in North County Kildare....

. Its final stretch westwards is through the Bog of Allen

Bog of Allen

The Bog of Allen is a large raised bog in the centre of Ireland between the rivers Liffey and Shannon.The bog's 958 square kilometers stretch into County Offaly, County Meath, County Kildare, County Laois, and County Westmeath. Peat is mechanically harvested on a large scale by Bórd na Móna,...

 via Derrinturn

Derrinturn

Derrinturn is a village in County Kildare, Ireland. It is located about from Dublin.The main road through Derrinturn is the R403 regional road.The village had a population of 1,138 in 2006.-See also:*List of towns and villages in Ireland...

 to Carbury

Carbury

Carbury , also formerly spelt "Carbery", is a village in north-west County Kildare, Ireland. It is situated in the on the R402 regional road between Enfield and Edenderry, near the border with County Offaly...

, where it terminates at the R402

R402 road

The R402 road is a regional road in Ireland, linking the M4 at Enfield, County Meath to the R420 east of Tullamore in County Offaly.-Route:It starts in the centre of Enfield; crosses the R148 and M4 at a complex junction at the edge of the town.Immediately enters County Kildare at Johnstown...

The route is 43 km (26.7 mi) long.