Before the opening of the Ankara-Istanbul high-speed railway in 2009, the Istanbul–Ankara railway was the busiest line in Turkey as well as the primary inter-city route, connecting Istanbul with Ankara through five provincial capitals: Izmit, Arifiye (a suburb of Adapazarı), Bilecik, Bozüyük and Eskişehir.

No passenger service is operated between Arifiye and Sincan (not including YHT high-speed trains).

Despite being mostly single track, the railway still has the longest multiple-track stretch in Turkey, excluding high-speed lines.

The first multi-track stretch begins at Haydarpaşa station in Istanbul and continues 44.1 km (27.4 mi) as a triple-track main to Gebze.

From Gebze, the line becomes a double-track railway and continues 123.5 km (76.7 mi) southeast to Pamukova.

The extension of the line to central Anatolia was revived under the new British investors, who formed an Anglo-American syndicate with Sir Vincent Caillard as the chairman, to finance construction.

Caillard was unable to gather the necessary capital forcing the Ottoman government to transfer construction to another company.