Locating Concentric Ring Roads in a City

A mathematical analysis is made of the optimal siting of concentric ring roads in a city so as to minimize the average distance travelled off the rings. It is found that although such ring roads are more effective if they are characterized by a higher speed of travel than the rest of the city, their optimal location is largely independent of such speed. Most of the benefit of using a series of concentric ring roads can be obtained from one or two well-placed ring roads. Optimization with respect to the average overall travel distance is also considered.