I've been accessing the AA Route Planner to get driving directions between our stops from Shannon to Dublin. I know that driving times are not what we're used to -- so -- do I need to double (or triple???) the travel times shown on that website??
What I do is take the mileage and divide by 35MPH. That will get you close unless you are on unusually fast roads, (not many of those between Shannon and Dublin) or unusually slow roads. You can find those anywhere.
Excellent advice from Bill. I have had trip computers on several cars in Ireland in the last few years. When set at the very beginning of my trip the average mph is always exactly 35 mph. That doesn't mean you won't be doing 70 in some places (or 100 kph!) but when you average out the whole trip it is always 35 mph. So that's your rule of thumb.