Line M8, officially referred to as the M8 Bostancı-Parseller line, is a rapid transit line of the Istanbul Metro. The line connects Bostancı railway station, on the southern coast of the Anatolian side, to Parseller, in the district of Ümraniye. At Bostancı, connections are available with intercity trains to destinations in Anatolia, as well as the Marmaray service across the Bosphorus.

The M4, officially referred to as the M4 Kadıköy - Sabiha Gökçen Airport metro line, is a 33.5-kilometre (20.8 mi), 23-station rapid transit line of the Istanbul Metro. It is colored deep pink on the maps and route signs. Running between Kadıköy and Sabiha Gökçen Airport, it is the first rapid transit line operating on the Asian side of Istanbul. The M4 mostly runs under State road D100, parallel to the Istanbul-Ankara railway and is entirely underground.