in
Kadıköy,
Istanbul. Unlike
motorways in Turkey, state highways do not have a minimum design standard. Despite the majority of the system consisting of four-lane, dual highways, other routes can be two-lane highways. Some routes, especially within major cities, have been upgraded to
controlled access highway standards; while other routes, such as the
D.650, between
Arifiye and
Bozüyük, and the
D.200, between
Eskişehir and
Ankara, consist of minimal at-grade intersections.
Bridges and
tunnels are common among the system, yet not as plentiful as on motorways.
Numbering All state highways have a three-digit designation preceded by a
D. The system is numbered based on direction and location. Route numbers range from
010 to
977, while
010 to
490 are east-west routes and
505 to
977 are north-south routes. Odd-numbered routes generally run north-south, while even-numbered routes generally run east-west. The only exception to this rule are four north-south routes,
D.550,
D.650,
D.750,
D.850 and
D.950, that have even-number designations. The second criterion is based on the geographical location of the route. For north-south roads, routes in the west will have lower numbers, while routes in the east have higher numbers. For east-west roads, routes in the north will have lower numbers that get higher towards the south. Main roads are designated as multiples of 100 and 50, with the exception being
D.010. Multiples of 100 are main east-west roads, while multiples of 50 are main north-south roads. D.010 is the only exception to this rule. ==See also==