Once upon a time--way back in 1871--Istanbul had some of the most innovative public transportation around. The Tünel funicular, which still carries tourists and residents alike up the steep hill from Karaköy to the southern end of Istiklal Caddesi, was the second underground subway line in the world, after London's. Maalesef (alas), it took 129 years for the city to open another one.
The historic ferry system plying the Bosphorus between Istanbul's Asian and European sides is as scenic and enjoyable as public transit gets, but land-bound options have lagged behind. Though bus and dolmuş (private mini-buses) routes crisscross the city, most face the same traffic woes as private cars. A light-rail metro, opened in 1994, and the finally expanded subway are generally clean, quick, and efficient, but fall far short of full coverage. Istanbul's yellow cabs are also one of the main options used to get around the city, but they are everything but CO2 neutral.
More info from Treehugger HERE