Following the coup, Turgut Özal was elected Prime Minister and his pro-automobile policies negatively impacted the project further.

The Turkish government mothballed the project in the early 1990s and instead chose to upgrade the existing railway to accommodate speeds of up to 200 km/h (120 mph).

A 33 km (21 mi) section of track between Eskişehir and İnönü was upgraded and expanded to a double-track line, opening in 1996.

[3] In the months following the agreement, the 2001 Turkish economic crisis hampered construction efforts and thus no progress was made on the railway.

Since Ankara was planned to be the center of Turkey's high-speed rail network, the existing track layout would not support increased train traffic.

Commuter rail service was temporarily suspended as high-speed and inter-city trains began to use the south two tracks, while construction progressed.

During this time, the railway was completely grade separated and a fourth track was added but construction of the full project did not progress very far.

[7] However, high-speed and inter-city rail service would be unaffected by the construction as they used the newly expanded north tracks to enter and exit Ankara.

[8] The first main section of the railway is the 225 km (140 mi) long stretch from Sincan, a western suburb of Ankara, to Eskişehir.

Passing through a cut-out, a viaduct and a tunnel, to navigate the hills west of Sincan, it crosses the existing railway at Esenkent, where a junction was built.

Crossing the river and the adjacent plains, the Sakarya Viaduct is the third longest bridge in Turkey, spanning 2,293 m (7,523 ft).

The State Railways approved testing on the route on 28 March 2007 and an agreement was made, two days later, with TÜV SÜD Rail Gmbh.

The second main section of the railway is the 188 km (117 mi) long stretch from Eskişehir to Köseköy, an eastern suburb of İzmit.

Between Eskişehir and İnönü, 30 km (19 mi) west, the existing railway was double-tracked in 1996 and was originally planned to be upgraded to allow speeds of 200 km/h (120 mph).

The expedited opening of the railway saw criticism from the opposition as well as the United Trade Union of Transport Employees (BTS).

[11] BTS criticized the move, claiming that the AKP government is skimming over proper construction and testing processes in an effort to gain political clout.

This 23 km (14 mi) bypass tunnels through the eastern Samanlı Mountains, rejoining the existing right-of-way just east of Sapanca.

To bridge this gap, high-speed trains use the existing railway, which follows the Sakarya River and runs around the Samanlı Mountains, via Arifiye.

[14] No progress on the Doğançay Bypass was carried out for several years as trains continued to use the existing railway between Sapanca and Geyve.

This accident happened when construction crews working on the widening of the adjacent D.650 state highway, blew dynamite to open up a path for the road.

[17] Just like the Doğançay Bypass, construction of Tunnel-26 did not continue for several years until 2017 when a new tender was awarded to IC İçtaş to finish the tunnel.

This decision was made since the area between the two cities are heavily urbanized and building a new dedicated line would require the acquisition and demolition of hundreds of properties.

Together with the infrastructure upgrades done in preparation for the high-speed railway, the tracks on this section can accommodate speeds up to 160 km (99 mi).

Unlike the situation in Ankara, due to Istanbul's dense urbanization, the State Railways were unable to add a fourth track along the entire line.

High-speed trains from Ankara would terminate at Pendik (24 km (15 mi) east of Haydarpaşa, until the remaining section of the railway was finished.

Originally expected to open in 2015, problems with the existing tender contract prompted Obrascón Huarte Lain to slow down construction works in 2014.

A new building was built over the south side of Ankara station to accommodate new high-speed train traffic, with an exclusive YHT concourse, shops and hotels.

Services on the line are all YHT high-speed rail trains operating at a maximum revenue speed of 250 km/h (160 mph).

This is the section where trains to Konya and Karaman use the Ankara–Istanbul high-speed railway, before diverging south at Polatlı junction.

As of mid-2022, YHT trains operating on the railway are as follows:[26] Alcatel won an $80 million contract to supply signalling services on the line, as well as interlockings and control systems,[1] while Thales Group has been contracted to supply an ETCS train control system for the Sincan—Eskisehir portion of the route.