The objective of this paper is to describe a technique to calculate fixed-time signal plans for traffic control systems that accommodate fluctuations on traffic flows. In the development of those plans, traffic volumes reflecting average conditions made on the basis of these values commonly overestimate the benefits of the implementation of fixed-time signal control plans because the variability of flows is not taken into account. The day-to-day, or between days, variation of traffic is not normally considered in the fixed-time plans and the daily systematic fluctuation, or within-day, variation of traffic is handled by the adoption of one of several possible procedures. In practice, single observations of flows are commonly used in place of the mean, and flows in different parts of the same network are sometimes observed on different days. Ways are investigated in which some measures of variability of traffic flows can be respected in the calculation of fixed-time signal plans. A method that incorporates the variability of the traffic flows in the calculation of a single fixed-time plan is developed. This was based on theoretical values and validated with real flows, collected in a purpose-specific field survey. This technique has been found to improve the efficiency of the fixed-time systems, handling both kinds of variation. Using explicit conditions of a variety of traffic flows on each link, this technique is suitable to be used as a standard feature for calculation of fixed-time signal plans that will be used under a range of traffic conditions. (A)
Abstract