Ireland and Northern Ireland

My tip is to NOT fly across the world on a redeye, arrive exhausted, then jump in a car and drive off (on the opposite side of the road that you're used to). Please give yourself a good night's sleep before attempting to drive.

My suggestion is to take a train or coach to Belfast and rent a car there. Arriving from a transatlantic flight means you might not be a safe driver. Also, renting the car in NI means you won't have to drive on roads with speed limits in miles per hour with a car that has a km/h-speedometer. When you are done in the north, take a train or coach across the border and rent a new car in Ireland.

We did it in the opposite direction September 2018, renting in Galway, then driving up to Northern Ireland, then down to Dublin, where we turned in the car. Leaving Belfast during morning rush hour was a bit hectic, but we were heading out of town, and the vast majority of cars were heading in to Belfast, not exactly quickly. It was good to be on the lighter traffic side of the road! But we had 3 weeks to make our way up and around, so we broke up the drive into shorter segments over lots of days. We also headed to the far north end of Ireland, passing thru Derry/Londonderry before reaching Belfast, so likely a different route than you’ll be taking.

The”M” and “A” highways will likely be wider and faster than the “N” roads, and less twisty. Is there one person who’ll be doing all the driving, or will you be including an Additional Driver in your rental contract? Either way, take a break every so often. And the passenger in the left front seat should serve as a navigator, and frequently check on the driver, reminding them to not drift too far left, where the edge of the road, and a possible brick wall or fence could be.

As a reminder, Northern Ireland uses Pounds Sterling, and the Republic of Ireland uses Euros. Both use litres for filling up with petrol, but it’s Miles Per Hour on the N.I. Speed limit signs, and Kilometres Per Hour in The Republic. When we crossed the borders, I don’t remember any signs or other indications alerting us to the change; speed limit signs were just suddenly different. Read your speedometer accordingly, and prepare to do some calculations regarding the odometer, if necessary.

When we crossed the borders, I don’t remember any signs or other
indications alerting us to the change; speed limit signs were just
suddenly different.

Then you must have crossed the border on some really small roads, usually there are signs: https://goo.gl/maps/1xq4oUPDbPFk4bQF8

Already noted above by Cyn.

thanks for all the great info and insights - so I do not need an international driver's license, correct?

anyone know about seeing the northern lights from points due north of Belfast along the coast? thanks again

You might get lucky but don't count on it, Ireland is too far south for the northern lights.