REQUIREMENTS FOR AUTOMATING SIGNAL TIMING PLAN DESIGN

The optimization of signal timing plans fbr isolated intersections is a complicated procedure. Most current techniques such as the Canadian Capacity Guile for Signalized Intersections and the Highway Capacity M anual rely on relatively simple analytical models to estimate the opti mum cycle time and green time splits, and leave the determination of t he optimum phasing scheme to the experience of the user. The main prob lem with current procedures is that, because of the large amount of hu man effort required, only a very limited subset of all possible soluti ons can be examined. In addition, none of the current procedures are e ntirely satisfactory in their ability to deal with complicated congest ed conditions. The interaction of shared lanes, permitted left turn mo vements, cycle times, and green time splits requires an iterative appr oach to the design of signal timing plans, if current methods are to b e used. Owing to the large number of calculations that need be done, c urrent procedures are, by and large, computerized. Using any of the pr ocedures currently available, each time a further iteration is needed, a new set of saturation flow rates or volume allocations must be manu ally coded into the input files of the computerized procedure. Thus, t he search for the optimum solution to a signal timing plan problem can require a large amount of engineering time. This article describes th e development of a notation and vocabulary that permits the automation of the logical decisions that must be made in order to optimize signa l timing plan design. As well, the information that is necessary to de fine the intersection geometry and volume demands, in order that an au tomated process can optimize a signal timing plan, is presented. The r ules that can be used to determine the phase of discharge of each lane and pedestrian demand volume, the lanes that are opposed by a conflic ting movement, and the movements that oppose traffic attempting to dis charge from a turning lane are also described. Finally, a brief descri ption of the framework of Signal Expert, a computer model that automat es all of the above, is provided.