Two friends gave me some advice about driving in Ireland. The first was from my friend who lives in Ireland:

• The car you rent will probably base the main speedometer and distance calculator on miles, but our speed limits and roadsigns are now in kilometers. So when you see that the speed limit on open roads is 100, that really means about 60mph, and so on. there will be a smaller kph scale on your speedometer, harder to read, but there all the same
• More or less zero-tolerance for drink driving here. The limit is about a slow beer, or a half beer, and after that it's not really on. So in choosing accommodation, if planning a drink or two, try to make them close together.
• Irish town names are generally anglicized from their old Irish names. So, for instance, Galway used to be Gaillimh. Many signs will use the Irish name rather than the English one, so watch out for that. Mostly you can guess - Ennis is Inis, Limerick is Luimneach, all fairly similar. Sometimes, though, there's no real relationship. Like Waterford is Port Lairge, which looks more like Portlaois, so be careful. Roads are numbered though, so that's a good guide
• If someone approaching you on the road flashes their headlights at you, it means slow down. There's either a hazard ahead, like a flock of sheep on the road or something, or there's a garda speed checkpoint round the corner.
• We call our police Garda, short for garda siochána, or guardians of the peace. They're unarmed, but have plenty of attitude. If pulled over for any accidental misdimeanour, the best greeting is a big smile, and "Evening, guard!". They like that.
• You'll see signs on the sides of the roads proclaiming how many people have been killed on the roads of that county in the last four years. The signs are erected by the NRA. This does not mean that right-wing gun-nuts are popping off Irish motorists. It stands for national roads authority
• You'll also see signs all over the place warning of major roadworks ahead. Sometimes there are, more often there aren't. Better slow down a bit, just in case.
• In some parts of Clare, bored youth no doubt related distantly to ate spend their time twisting roadsigns for their own perverse amusement. Get yourselves a road map.
• Times don't relate well to distance out the West. A really good website for planning journey times and route is http://www.theaa.com/travelwatch/planner_main.jsp?database=I
• The worst drivers are nuns and men in flat caps. Give them lots of space if you can. Nuns are harder to recognise these days, except by their driving.

Then I received the following things to remember from a friend who had visited Ireland a few years ago.

• Major highways in Ireland make 101 (in the Pacific Northwest) look like an interstate. Except for the motorways around Dublin, expect a highway to be two lanes, no shoulders, and stone walls on the side. If you're lucky, you might replace one of the walls with a cliff.
• Speed limit is 60 MPH, but you're unlikely to get near it. If you average 40, you're doing great.
• Speed limits are marked below the national speed limit. There's an "end of limited speed" symbol which means you can drive 60.
• Signs are sometimes in kilometers, sometimes in miles. Oh well.
• Passing is not for beginners.
• An Audi A4/Volkswagen Passat, which looks midsize in the US, looks huge in Ireland.
• Couch == bus. Lorry == truck. Bonnett == hood. Caravan == camper trailer. Garage == car park. Etc.
• Couches can actually fit in a lane. Believe it or not.
• Car parks often have signs telling you how many open spaces are in the park.
• Gas is priced in liters, so it actually costs 4X as much as you think at first. Fortunately, it's 95 octane, rather than the wimpy stuff we get here.
• Sheep have right of way. Yes, there are sheep on the highways, especially at night. Imagine sheep wandering across I-5 between Portland and Seattle, it's kinda like that. Drive carefully.
• Your first roundabout will scare the living shit out of you. Don't be ashamed to leave it immediately. Roundabouts range from 4 lanes deep near big cities to a yellow circle painted in the middle of an intersection. Same rules always apply: cars in the roundabout have right of way. And don't forget, on the big ones, you can actually go around again. Roundabouts are your friends. In the Republic, there's no limit on the number of times you can go around (I think you can only go around twice in the north).
• This: http://www.swindonweb.com/life/lifemagi1.jpg is real. Fortunately, it's in England, not Ireland.
• Get the spelling of wherever you're headed. The pronunciation may not make any sense. For instance, Dun Laoghaire is pronounced "Dun(e) Leary".
• Signage can be confusing, until you get used to the way it works.
• Have a navigator. Navigator is essential for telling you where to get out of the roundabout. Get directions like "1st exit", "2nd exit", etc. Also, "9 o'clock", "11 o'clock", etc can be useful.
• Cities are evil. Don't drive there. Dublin is for pedestrians and taxis, not silly Americans in cars. Trust me, drive there and you'll be sorry. Don't venture inside the M50.
• When you get to a corner, look right first, not left. In cars and on foot.
• Cars with a big red L in the rear window have learners permits. They're probably still better than you on the left.
• Take a drive the first day. We got our car in Galway, and headed north to Mayo. Great way to get used to driving on the left.
• Practice driving stick in the US before you go there, if you're used to an automatic. Chances are you'll have a stick there, and you don't want to try to learn that and drive on the left at the same time.
• All the controls are in the same place, except the stick shift. Turn signals, pedals, whatnot. But that stick in the left hand is entertaining.
• Germans are as confused as you are. Just more aggressive and in an RV....