Traffic signal capacity and timing analysis techniques are presented as an aid for detailed geometric and operational design of signalised intersections. The background to these techniques is provided to permit the development of a better understanding of the subject. The report introduces several changes to the existing methods, a basic change being from phase-related methods to movement-related methods. A critical movement identification method is presented as a procedure which automatically satisfies minimum green time constraints and allows the use of different degrees of saturation for different movements as a measure of priority and restraint. There are changes in the saturation flow estimation method, and there is an emphasis on the use of measured saturation flows in practice. Detailed discussions of opposed turn, lane utilisation and short lane problems are presented in the section on saturation flows. New formulae are given for predicting delay, number of stops and queue length, which are applicable to both under-saturated and over-saturated conditions. Formulae for calculating a practical cycle time, an approximate optimum cycle time using a stop penalty parameter, and green times in both simple and complicated multiple overlap cases are also included. The prediction of operating characteristics and calculation of signal timings for vehicle actuated and co-ordinated signals are discussed separately in appendices. All other aspects of this report are applicable to both fixed-time and vehicle-actuated, isolated and co-ordinated signals. Signal design questions in general, and the question of design period in particular, are discussed and a recommended design procedure which brings together various methods described in the report is given (Section 8.3). Suggestions for simplified analysis which can be adopted for planning and preliminary design purposes are included. Numerical examples are presented to illustrate the methods described in the report. (Author/publisher)
Abstract