OPTIMAL CONTROL OF OVERSATURATED INTERSECTIONS: THEORETICAL AND PRACTICAL CONSIDERATIONS.

The problem of optimal traffic signal control of congested intersections with queue length constraints is discussed. Isolated intersections as well as a system of congested intersections are treated. The latter case is not a simple extension of the case of the single intersection since it involves consideration of turning volumes, travel times and queueing storage between intersections. It is shown that optimal signal operation requires, in general, variable cycles and splits when queue length constraints are imposed and that at an isolated intersection optimal signal operation resembles that of traffic-actuated signals when the volumes drop below saturation level. Furthermore, it is shown that, for a system of intersections, signal co-ordination is necessary and can be obtained according to relationships developed here. Numerical examples are presented to illustrate the applicability and effectiveness of the theory to real-life situations. Sensitivity analysis reveals that the optimal control policy results in substantial delay savings as compared to conventional methods even if the expected demand is substantially overestimated or underestimated. /TRRL/