The last decade has seen an increasing realization that in the future large-scale grade-separated highway construction in urban areas will be severely limited. Instead, the emphasis has changed to traffic management and the optimal use of existing facilities by the geometric re-design of roundabouts and the use of computer control to improve flow through signal-controlled networks. This trend has led to increasing interest being paid to the signal-controlled roundabout which combines the separation of traffic conflicts with accurate computer control. This paper reviews the theoretical concepts which have so far been expounded on the signal-controlled roundabout. A detailed explanation is given of 'conflict separation' and 'natural cycle time', and a comprehensive example is included to illustrate how these concepts can be applied to a specific scheme. Details are given of the performance of signal-controlled roundabouts in Bradford and in Huddersfield, west Yorkshire. The paper goes on to describe a computer model which has been developed to simulate traffic flow in and around a signal-controlled roundabout. A before and after study is conducted utilizing the simulation model and the department of transport's model for roundabouts, ARCADY. A comparison of queue lengths and delays before and after the installation of signal control is made and conclusions drawn. In addition, the improvement in the level of service after the installation of signals is discussed using the distribution of individual vehicle delays as a basis. (a) for the covering abstract of the seminar see IRRD 273510.
Abstract