Looks like careless traffic regulation at Howth Junction. Previous DART was on time but the one which follows appears to have been routed ahead and then held resulting in delays to both the DART and the Dundalk service.
Later in the morning further poor traffic regulation at Howth Junction resulted in the 0800 from Belfast taking 21 minutes to negotiate the 9 miles from Malahide as a DART was allowed run immediately ahead of it from Howth Junction. The 45 miles from Dundalk took about 38 minutes ! Roll on the interconnector and the whole lot should just grind to a halt.