The 1985 highway capacity manual (HCM) signalised intersection analysis method has provided a powerful technique for determining how well an intersection will operate given the traffic volumes, intersection configuration, and signal timing. It has been less successful in producing a practical technique for determining the service volume for a specified level of service. The main problem is the irreversibility of the delay equation upon which the level of service is based. This paper explores a number of numerical analysis techniques for solving the delay equation in reverse. Specific computational procedures are demonstrated for determining the traffic volume which will produce a given delay. Both manual methods, using a worksheet, and computerised solution are presented. The main problem with determining service volumes results from the interactions among the independent variables of the delay equation, not from the need for a mathematical solution to the equation itself. Because of the complexities of the HCM technique, there are discontinuities in the volume-delay relationship. There are situations which require the simultaneous solution of two equations, and there are situations in which a unique solution does not exist. Several simple computational modules were developed to deal with specific situations covered in this paper. These are demonstrated using several sample calculations from chapter 9of the HCM.
Abstract