The Rationale of a Ring Road
Ring roads have become a common infrastructure in the development of large metropolitan areas. Their impact on the urban spatial structure is mainly through radial development pattern and the setting of commercial, residential and industrial activities nearby highway interchanges. The decreasing dynamism of central areas is often linked with the emergence of peripheral centers that gaining from improved accessibility with the construction of ring roads. As shown on the synthetic example on the above figure, prior to the construction of a ring road, going from point A to point B would take 30 minutes, with delays mainly imposed by having to go through the central area (e.g. narrow roads, speed restrictions, traffic lights, etc.). Once a ring road has been established, travel time between point A and point B is reduced to 20 minutes since congested areas are by-passed. Also, since ring roads tend to be limited access highways, they can confer further time improvements to cross a metropolitan area.