Due to the geography of the province lying elongatedly on peninsulas, major routes follow a west-east axis.
The highway D100 which closely follows the coast of Marmara on both sides of Bosphorus, and the motorway/toll-road O-3/E80 which lies in parallel with D100 a few km inland to north, are the main backbones of the traffic in the province and also are the main roads connecting it with neighbouring regions, turning into heavily congested urban roads, especially in the case of D100, when crossing the city of Istanbul proper.
D020 and D010 which is essentially a continuation of D020 through Belgrad Forest, lie further north of O-3/E80, mostly traversing wooded rural areas of northern parts of the province, on both sides.
A few daily trains from Sirkeci Station connect a number of remote inland villages in addition to the town of Ãatalca to Istanbul. Other than the line in the city of Istanbul itself, which lies along the Marmara coast, there is no railtrack on Kocaeli side, so your option of getting around by train there is pretty much limited to suburban trains plying between HaydarpaÅa Station and Gebze out of provincial borders.
Outlying towns have fairly frequent bus/minibus connections with Istanbul. The buses to towns in western parts of the province depart from Yenibosna metro station, one of the westernmost stations on M1 line. Villages along northern coast are served by buses and minibuses from Sarıyer, the northernmost neighbourhood of city on Bosphorus, while the buses to towns and villages on eastern peninsula usually have their terminals in Harem, the main bus station on Asian Side.
