I can't see many people from Cork driving to Dublin to catch a flight to Madrid. Especially when you can get a spin to Cork airport, and catch a ryanair flight to Dublin for less then the cost of the fuel, tolls, and parking costs involved in driving to Dublin. Tolls for the M8 at Watergrasshill and the M50 round Dublin would cost almost €10 return, and then there is the car park fee of around €8 a day, plus fuel costs of about €40. €58 return for driving up and down to Dublin?
If your destination in Dublin is the airport or anywhere near the airport, you'd be mad to drive.
Better, quicker, and cheaper to fly. Alternatively fly to Barcelona direct from Cork and connect by AVE to Madrid which will take you about three hours.
I prefer to fly into Cork at the end of a trip rather then have to face a drive from either Dublin or Shannon.