The current timetable mess on the Belfast line shows Irish Rail's contempt for Enterprise passengers and it's near total lack of ambition for the route.
Services performance can be broken down into a number of categories
1) Trains which cannot run to time unless preceding trains run early, e.g. 0645, 1035 & 1235 from Belfast. As far as I can ascertain only one of these trains has arrived at the published time since April 10th and then on only one occasion.
2) The 0930, 1120, 1320, 1520, 1650 and 2050 from Dublin which idle at or outside Drogheda and Dundalk for anything up to 15 minutes or on occasions depart early.
3) The 0800, 1405, 1605, 1805 and 2005 from Belfast which generally run close to time and even arrive early on occasion.
4) The 1850 from Dublin which struggles to reach Drogheda in 45 minutes, not far off double the journey time of 27 minutes which applied in 1997 and which despite the relatively poor condition of the line between Dublin and Malahide is still achievable. An unobstructed path is available at 1905.
The elephant in the room is poor DART performance and in particular the almost 25% increase in journey time since the service commenced in 1984.
Most of the increase in rail usage in the Dublin area over the decade to 2008 was not DART in any event yet non-DART services are being severely penalised to support a vanity project which is impractical, of little benefit and not required to meet demand.