Vehicle responsive traffic signal control

A number of attempts have been made to develop discrete time optimising approaches to traffic signal control. The first and seminal development was the DYPIC program, followed bythe OPAC and PRODYN programs. These approaches are characterised by the potential absence of any stage sequence constraints (when there are more than two stages), although they do retain stage structure. For a prespecified lookahead period, the optimal sequence of decisions with respect to when and how to change stage is sought. In general, dynamic programming has been used to solve the problem. DYPIC uses backwards dynamic programming, as does one version of OPAC. PRODYN uses forward dynamic programming. This paper presents the optimisation problem in graph theoretic terms. A tree-building approach to optimisation is described and shown by simple examples to be more efficient than dynamic programming.