There's no train connection with Abu Dhabi Airport.
Car and bus
Abu Dhabi Airport is situated 32 kilometers east of the city center. The airport is easily accessible by rental car. From the city three roads lead in the direction of the airport: Khaleej Al Arabi (road number 30), Sheikh Rashid Al Maktoum Street (road number 2) and Salam Street (road number 8). The way to the airport is clearly signposted along all these roads.
The regular bus service 901 leaves every 40 minutes from the airport to Abu Dhabi. A ticket costs 3 dirham and the bus takes about 5 quarters of an hour to reach the terminus near the old fish market on Al Nasr Street.
There are also express busses from Etihad Airways to Dubai, Al Ain and Sharjah. These busses are free for those travelling with Etihad Airways.
Car rental Abu Dhabi Airport
You can find the counter for car rental companies in Skypark Plaza opposite Terminal 3. Six rental companies are present at Abu Dhabi Airport: Budget, Dollar, Europcar, Hertz, Thrifty and Payless. You can also book a rental car in advance using the service provided by EasyTerra; they compare the rates of several providers in a single quote.
Outside the Arrivals hall there are many taxis of two companies, Fast and National. Both charge a fixed rate for a trip to Abu Dhabi and other destinations. Count about 70 dirham for a trip to Abu Dhabi; travel time takes well over 30 minutes.
Parking lots and the Sky Park parking garage for short to medium-term parking (max. 7 days) can be found outside Terminals 1 and 3. If you want to park your car at the airport for more than 7 days you are referred to the parking lot near Terminal 2.