Otoyol 4

The O-4 begins at the intersection with the O-1. The next interchange is in northern Ataşehir with the O-2 .^[1] After the motorway crosses Necip Fazıl Boulevard, the last toll-free exit in Istanbul (K1), the O-4 becomes a toll-motorway at the Çamlıca toll booths. The first tolled exit is exit K2, which is the Samandıra-Kartal connector, that is the first of several connections to the D.100.^[2] Exit K3 connects to Fatih Boulevard in Sultanbeyi.^[3] The interchange with the O-7 is located just as the O-4 enters the district of Pendik. Exit K4 is located right on the eastern border of the Pendik district and connects to the Sabiha Gökçen Airport.^[4] After exit K4, the O-4 enters the last district in Istanbul, Tuzla. Exit K5 (Orhanlı junction) also offers a connection to the Sabiha Gökçen airport as well as the Kurtköy-Pendik connector.^[5] The O-4 continues through northern Tuzla, passing through mostly industrial parks until leaving the Istanbul Province and entering the Kocaeli Province.

After crossing into Kocaeli, exit K6 is the Şekerpınar-Çayırova connector in Şekerpınar.^[6] The O-4 traverses through northern Gebze until exit K7, which is a direct connection to the D-100.^[7] After crossing over the D-100, the O-4 interchanges with the northern end of the O-5 at the unnumbered Mualimköy junction.^[8] Following the junction, the motorway runs along the heavily industrialized northern shore of the Izmit Bay with exits at Diliskelisi (K8)^[9] and Hereke (K9, K10).^[10][11] Between Hereke and Körfez the motorway runs directly next to the D-100 and the Istanbul-Ankara railway along the shoreline until the motorway enters Körfez. Once in the city, Exit K11 connects to the D.100.^[12] Shortly after K11, an unmarked exit to a KGM employee housing facility.^[13] The exit is not open to public traffic although cars may use the overpass to make a U-turn. After passing a service area, the O-4 enters the city of İzmit. Exit K12 connects to the D.100 but only for traffic from/to Istanbul. The route then heads north and travels around the hilly northern perimeter of the city, passing through two tunnels and a viaduct. The O-4 crosses over the D.605, which can be accessed via Exit K12.^[14] After bypassing Izmit, the motorway heads southeast, crossing over the D.100 (Exit K13^[15]) in Bahçelievler. After the exit, the route enters Sakarya Province.

Otoyol 4 parallels the Istanbul-Ankara railway along the southern shore of Lake Sapanca except for its short bypass around the town of Sapanca. Exit K14 connects to the town, via İzmit Avenue.^[16]

• Istanbul road map
• Ankara road map