Citation

Lu GX, Zhang Y, Noyce DA. Transp. Res. Rec. 2011; 2259: 96-111.

Copyright

(Copyright © 2011, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

10.3141/2259-09

PMID

unavailable

Abstract

One critical issue of traffic control is the optimization of signalized intersections for improved multimodal safety and operations. Accommodating pedestrian traffic at intersections is challenging because the demands of multimodal service compete fiercely on limited green time resources. The "Highway Capacity Manual" prescribes that the parallel vehicle green must exceed "Walk" plus pedestrian clearance interval (PCI) timed by a design walking speed. This static PCI timing is unsafe because seniors and children are likely to be slower than the design pedestrian. Furthermore, a vehicle-flow issue arises when the prolonged PCI exceeds the operationally efficient parallel green: additional vehicle right-of-way, unnecessary for operational efficiency, preempts green time from conflicting phase(s) and increases intersectionwide queuing delays. Queuing delays necessitate a trade-off between competing multifaceted traveler needs. Fuzzy logic control (FLC) proves effective, flexible, and robust in handling competing objectives. With the dynamic PCI concept, this research developed an intelligent traffic signal system that performed friendly pedestrian accommodation and also incorporated FLC into fulfilling multifaceted vehicle needs. The potential benefits from the new system optimized with a genetic algorithm were quantified through a comparison with a standard dual-ring, eight-phase, vehicle-actuated controller, conventionally cited as NEMA (National Electrical Manufacturers Association) control. Microsimulation experiments revealed that the current countermeasure, which lowered PCI timing design speed to strengthen crossing safety, was operationally deficient. The existing timing standard cannot offer adequate safety for all pedestrians, and the NEMA system omits multifaceted vehicle needs in control logic. In contrast, the FLC system fully protects all pedestrians through dynamic PCI and smartly serves manifold vehicle needs well. The FLC system outperforms the NEMA control by embodying a reasonable trade-off between competing objectives in the management of an isolated intersection.