The Istanbul–Ankara railway is a long electrified railway in Turkey. The line connects Turkey's largest city, Istanbul, to the capital and second largest city, Ankara; making it one the busiest railways in the country in terms of passenger and freight rail traffic. The railway runs parallel to the Ankara-Istanbul high-speed railway and in several sections, the railway hosts YHT high-speed trains. The line begins at Haydarpaşa Terminal in Istanbul and ends at Ankara railway station in Ankara. 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, Bilecik, Bozüyük and Eskişehir. In 2008, 65% of all inter-city service used the railway entirely or at one point. The Haydarpaşa suburban and the Ankara suburban operated commuter service along the line in Istanbul and Ankara respectively. Freight rail traffic is heavy on the line as the railway connects to the Port of Haydarpaşa and the Port of Derince as well as other private ports and passes through several important industrial regions in Turkey. In 2015 the railway carried 6.1% of all freight rail traffic in Turkey. Due to the construction of the Ankara-Istanbul high-speed railway, Marmaray and Başkentray, traffic on the railway declined greatly due to sections being closed down for several years. As of November 2016, the Haydarpaşa-Pendik section is still closed to all traffic as the rehabilitation of the line is still underway. No passenger service is operated between Arifiye and Sincan.
Infrastructure
Even though most of the line is single track, it still has the longest multiple track stretch in Turkey, not including high-speed railways. As of 2016, of the railway is double tracked or more, while the remaining of the railway is single track. Out of the 225 km multiple track sections, is double track, is triple track while is quadruple track. The multiple track sections are not all connected as there are three separate sections. The first segment starts in İstanbul at Haydarpaşa and continues for to Arifye, a suburb of Adapazarı. The next segment is in Eskişehir. This segment starts at İnönü, travels east through Eskişehir and ends at Hasanbey. The section between Eskişehir and Hasanbey is triple track as the line shares tracks with the high-speed rail line. The third section is Ankara. This segment is triple track and quadruple track in the city center. This part begins at Sincan along with the Sincan-Kayaş commuter service and travels east. After Etimesgut yard, the line becomes a 4 track line. This segment ends at Ankara's Central Station along with the main line. Trains operating on the Istanbul–Ankara railway use the fastest speeds allowed on conventional lines in Turkey. These speeds are up to, although some trains speed up to during straight segments around Eskişehir and between İstanbul and İzmit. The line will be upgraded after 2013 to accommodate new traffic once the Marmaray project is complete. This upgrade will allow trains to operate at speeds up to.
The first completed section of the railway was a section from Kadıköy in Istanbul to Izmit. This railway was built by the Ottoman Empire, financed by the Ottoman Bank and is the only railway that was built by the imperial government itself. The purpose of the railway was to connect the several towns along the northeastern coast of the Marmara Sea. Further plans to extend the railway into central Anatolia and as far as Mesopotamia were drawn up but since managing the line was financially difficult for the Ottoman Bank, the plans were scrapped and the operation of the line was sold to a British company in April 1880. 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. The concession was awarded to Georg von Siemens on 8 October 1888 and would be financed by the Deutsche Bank. In preparation for the undertaking, von Siemens formed the Ottoman Anatolian Railway on 4 October 1888 to build and operate the railway for 99 years. The CFOA started construction further from Izmit in May 1889 and purchased the Istanbul-Izmit railway for 6 million CHF.
