Traffic in Istanbul can be manic; expect a stressful drive because you will be cut off and honked at constantly. The city currently holds more than 1,500,000 automobiles and there is a strong demand for building of new or alternate highways.
If you've arrived in Istanbul by car, and you're not familiar with the streets, it's better to park your car in a safe place and take public transportation to get around.
The city, lying on two different continents and separated by the Bosphorus, is connected by two bridges. The bridge on the south, closer to the Marmara Sea, is called the "Bosphorus Bridge". The bridge closer to the Black Sea is named "Fatih Sultan Mehmet Bridge" and is longer than the first one. Both are toll bridges, and you must pay a fee to cross.
Since 2006, the Bosphorus Bridge toll stations do not accept cash, and payment must be made using electronic cards, either manually (KGS) or automatically via a transponder mounted on the front of the car (OGS). The Fatih Sultan Mehmet Bridge does not accept cash either, only KGS or OGS. The minimum amount of credit which can be purchased for a KGS card is 50 Turkish Lyra (October 2012).
On weekdays, drivers should be aware of potentially hour-long traffic jams on the highways leading to both bridges, particularly heading west in the mornings and east in the evenings, since most people live on the Anatolian side but work on the European side.
There is a great shortage of parking in Istanbul, and existing lots are quite expensive. You will see many cars parked on the sides of the road, in front of garage doors even.
Drivers unfamiliar with the city should also be aware that street signs are rare. It is a common thing to pull over and ask for directions, something the natives and taxi drivers do quite often.
