Initially you leave Dublin on the N4/M4, which is the Sligo road. Depending on where in county Roscommon you are going, you have a choice when you get to Kinnegad, in the midlands of Ireland. You can take the Galway Road, which is the M6 if you are heading to the southern half of Roscommon, or continue on the M4 if you are going to the northern part. If you are going to Roscommon town, you could go either way, as it is central in the county, though the M6 to Athlone and then the N61 to Roscommon town would be slightly better.
From Roscommon town to Dublin Airport is about 100 miles or 162 kilometres. Depending on where specifically in the county of Roscommon you are going to, the distance would differ, but not by a large amount.
It depends on which part of Dublin to which part of Louth and how you are travelling but by car from the centre of Dublin using the M1 motorway it would only take 30-40 minutes to Drogheda, the first town in Louth.
M4.
There is a motorway between Cork and Dublin, using the M8 and then the M7.
Blarney is in Cork, so to drive there from Dublin airport would take at least 3 hours on the motorway and could be more in heavy traffic.
In good traffic it can be done in about 2 hours.
You can get there by motorway. You take the M7 to just south of Naas and from there you join the M9 which brings you to Waterford.
There are various routes from Dublin to Athlone. The best is to go by the M4 motorway to Kinnegad and from there to Athlone by the M6 motorway. Going that way it is about 77 miles. That would be about 125 kilometres.
120 miles taking this route:Take N7 WATERFORD, from Dublin, to M7, and then continue on the motorway to M9 (to N10) to KILKENNY at J11.Take M9 to N10 to KILKENNY at J8.Take N10 to Kilkenny.
At average speeds and using the motorway system it takes just under 4 hours from the edge of Dublin city to Dingle. At peak times it may take longer, especially from 3pm onwards.
Galway, Roscommon, Offaly, Tipperary for starters
You will find timetables at the Iarnród Éireann website below. It is the train that runs between Westport and Dublin.