Title: Optimal cycle length formulas for intersections with or without transit signal priority
Authors: Wolput, Bart ×
Christofa, Eleni
Tampère, Chris #
Issue Date: 2016
Publisher: Transportation Research Board, Commission on Sociotechnical Systems, National Research Council, National Academy of Sciences
Series Title: Transportation Research Record vol:2558 pages:78-91
Article number: 16-1804
Abstract: Webster’s formulas for optimal green split and cycle length are a common way for optimizing signal
settings at signalized intersections. However, these equations were intended to be used for optimizing
signal timing plans for fixed-time isolated intersections, balancing phase utilization and minimizing
car delay for undersaturated conditions. These formulas are less appropriate for near-saturated and
oversaturated conditions due to the asymptotical behaviour of the cycle length formula when the
intersection flow ratio approaches one. These formulas were not conceived for operation under transit
signal priority (TSP) strategies. The main objective of this paper is to develop formulas for the optimal cycle length that can be applied when mild TSP strategies like green extension or green extension with phase rotation are implemented and/or when the intersection operates under near or oversaturated conditions. A formula for optimal cycle length is developed as a function of lost time and intersection flow ratio. It is applicable both with and without TSP. It appears that for green split, no new formulas are required as the Webster equisaturation approach is near-optimal. The cycle length formula is
validated for undersaturated, near-saturated, and oversaturated conditions with and without transit
signal priority for two-, three- and four-phase signalized intersections. Compared to Webster’s
formula the proposed formula shows a significant improvement in reducing person delay. Compared to the Webster formula there is a 6%, 17% and 22% less average person delay and a 16%, 27% and 35% less average bus delay for two-, three- and four-phase signalized intersections respectively.
ISSN: 0361-1981
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Centre for Industrial Management / Traffic & Infrastructure
× corresponding author
# (joint) last author

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