Knowledge-based system for design of signalized intersections

For an efficient traffic operation in intelligent highway systems, traffic signals need to respond to the changes in roadway and traffic demand. The phasing and timing of traffic signals requires the use of heuristic rules of thumb to determine what phases are needed and how the green time should be assigned to them. Because of the need for judgmental knowledge in solving this problem, this study has used knowledge-based expert-system technology to develop a system for the phasing and signal timing (PHAST) of an isolated intersection. PHAST takes intersection geometry and traffic volume as input and generates appropriate phase plan, cycle length, and green time for each phase. The phase plan and signal timing change when intersection geometry or traffic demand changes. This paper describes the intended system functionality, the system architecture, the knowledge used to phase and time an intersection, the implementation of the system, and system verification. PHAST's performance was validated using phase plans and timings of several intersections, including the examples within the Highway Capacity Manual (HCM). A comparison of delays and levels of service of the phase plans and signal timings generated by PHAST to those of HCM indicate that very comparable optimal solutions are being generated by the PHAST system. A potential use of the PHAST system would be in the design of demand-responsive intersection controllers for intelligent-vehicle highway systems (IVHS).