There's no train connection with Istanbul Sabiha Airport. It's proposed however to extend the new light rail line from Kadiköy (Asian part of Istanbul) to Kartal to the airport.
Car and bus
The airport is situated 40 kilometers southeast of the Asian center of Istanbul (Kadıköy) and 45 kilometers southeast of the European part. The airport is easily accessible by rental car. The airport lies along the road that connects two freeways: the so-called TEM Highway (E80) and the E5, which both lead to Istanbul. The way to the airport (or to Istanbul) is clearly signposted on both roads.
Shuttle buses connect Sabiha Airport with both the Asian and the European part of Istanbul. More information via telephone number +90(0)216 411 8600. There are also several regular buses from the company IETT to for example Levent, Bostancı and Kadıköy.
Car rental Istanbul Sabiha Airport
You'll find many counters of car rental companies in the Arrivals Hall. No less than nine rental companies are present at Istanbul Sagiha Airport: Avis, Bostanci, Budget, Europcar, Hertz, Nord, National, Payless and Sixt. You can also book your rental car in advance using the service provided by EasyTerra; they compare the rates of several providers in a single quote.
There are taxis outside the Arrivals Hall (Tel. +90(0)216 588 0035). They all have a meter. For a ride to Istanbul's center you pay approximately 90 lira. You can find the current taxi fares online on the airport's interactive transport website (also for bus connections).
A parking garage with places for almost 5000 cars is connected with the terminal. For the first hour you pay 8 lira, to park 1-3 hours 10 lira, to park 3-6 hours 16 lira and 25 lira for a whole day.