Attiki Odos, or Attica Tollway, is a modern motorway extending along 70 km. It constitutes the ring road of the greater metropolitan area of Athens and the backbone of the road network of the whole Attica prefecture. It is an urban motorway, with two separate directional carriageways, each consisting of 3 lanes and an emergency lane (hard shoulder). The suburban railway of Athens has been constructed in the central reservation of the motorway. Attica Tollway constitutes a unique piece of infrastructure, even in European terms, since it is essentially a closed toll motorway, within a metropolitan capital, where the problem of traffic congestion is acute.