Drive Bushmills to Dublin airport

You have to book a time at Newgrange.

G3RRY, yes, thanks. There is a 3 hour tour and a 2 hour tour. Unfortunately, it seems the 2 hour tour is right away at the start of the day. I'm not quite sure if people go back to the visitor center if they didn't finish or if that is not an option.

The tour buses leave from and go back to the Visitor Centre, so you can go back in to see more of the exhibition and also visit shop cafe and toilets.

You could also, on your way down, drive through The Dark Hedges - a cool, tree-lined road about 20 mins into your drive outside Bushmills.
We took about 2hrs to visit Newgrange, which was plenty of time. We went in off season (April) so had no problems getting tickets a bit last minute (most likely not the case for September.)
I will say it's roughly at 3 hr drive without traffic, and there usually is a lot of traffic. So your drive most likely will take longer than you think. And there are many places with road construction currently, which further slows down the routes. Just something to factor in if you plan to visit both Newgrange and Trim.

Driving Bushmills → Dublin Airport

This route takes you from Northern Ireland (UK) into Ireland, so you’ll cross from miles per hour (mph) into kilometres per hour (km/h) — but there’s no formal border checkpoint.

🇬🇧 Northern Ireland UK — MPH

Once you leave Bushmills and are driving in Northern Ireland:

Speed limits are in miles per hour (mph)
Typical limits:
30 mph (towns/villages)
60 mph (rural roads)
70 mph (dual carriageways/motorways)

You are driving under UK road rules, and this follows the official guidance in the UK Highway Code.

👉 Official reference:
UK Highway Code : https://www.nidirect.gov.uk/articles/highway-code

🇮🇪 Crossing into the Republic of Ireland — KM/H Zone

As you drive south toward Dublin, you will cross an invisible border between Northern Ireland and the Republic of Ireland.

There are usually:

No stops
No customs checks
No passport control
Just a small sign and road marking changes

The key change is speed units:

Road signs switch to kilometres per hour (km/h)
Road markings and signage may also change style and language (English + Irish)

Typical Republic of Ireland speed limits:

50 km/h (urban areas)
80 km/h (regional roads)
100 km/h (national roads)
120 km/h (motorways)
⚠️ The BIG thing Americans need to adjust to
MPH vs KM/H confusion

This is where most visitors get caught out:

70 mph ≈ 110 km/h
60 mph ≈ 100 km/h
50 mph ≈ 80 km/h
30 mph ≈ 50 km/h

Many rental cars in Ireland show both units, but some only show km/h, so check before you leave Belfast.

A simple rule:

In Ireland, the number on the sign is usually LOWER than what Americans expect because it’s km/h, not mph.

🛣️ What the “border crossing” actually feels like

Driving from Northern Ireland into the Republic is often described as:

One moment: MPH signs (UK system)
Next moment: KM/H signs (Irish system)
No dramatic stop or inspection point

You may notice:

Road signs changing format
Bilingual signs in the Republic (English + Irish)
Different motorway numbering style (M roads in both, but signage style changes slightly)

But functionally, it feels like crossing a county line in the US, not an international border.

🚗 Practical driving tips for the whole journey
Drive on the left-hand side in both NI and Ireland
Keep your focus on speed limit sign changes when you cross the border
Use cruise control if your car has it — it helps with km/h adjustment
Be careful on rural roads around Bushmills — they can be narrow and winding
Watch for sudden drops from 100 km/h → 80 km/h zones in the Republic
🧭 Route reality check

Bushmills → Dublin Airport is roughly:

3.5 to 4.5 hours depending on traffic
Mostly good roads (A roads + motorways)

Main motorway sections:

A26 / M2 (NI)
M1 (NI → Dublin corridor)
M50 ring road around Dublin (can be busy)