For the majority of its time in service, it was the second-busiest route of the Turkish State Railways, after the Adana-Mersin Regional.

Trains served a heavily populated region on the north-east shores of the Sea of Marmara and the Sakarya plain.

The Regional service also passed through important districts of Istanbul such as Kadıköy, Maltepe, Kartal, Pendik, Tuzla as well as Gebze, İzmit and Adapazarı.

[2] The train used to service Coşkunoğulları station until the TOE (Turkish Automotive Industry) factory was closed in 1991.

Before TCDD rehabilitated its old intercity and regional fleet, the electric locomotives which pulled trains were the E40000 or the E52500 series, and cars consisted of black and red regional cars that were built by TÜVASAŞ primarily for this service.