Citation

Parsonson PS. Transp. Res. Rec. 1978; 681: 34-42.

Copyright

(Copyright © 1978, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

At signalized intersections where approach speeds are 56 km/h (35 mph) or higher, drivers face a "dilemma zone." If the yellow signal comes on while the driver is in this zone, a decision to stop may result in a rearend collision or a sideswipe. The opposite decision, to go through the intersection, might produce a right-angle accident. For such an intersection, the traffic engineer needs to select a detector-controller configuration that will (a) detect an approaching vehicle before it enters the dilemma zone and either (b) extend the green signal to provide safe passage through the zone or else (c) end the green signal when the vehicle is still upstream of the dilemma zone and thereby provide adequate stopping distance. A major research project examined in detail a number of advanced detector-controller designs. The resulting design manual has systematically integrated into a single publication the available knowledge on the subject. This paper condenses the author's contribution to the design manual, elaborates on certain points incompletely treated by it, and proposes a new configuration. Current knowledge of dilemma-zone boundaries is reviewed, a classification of controllers and detectors and a taxonomy of detector-controller configurations are provided, and research data on the effectiveness of green-extension systems are summarized. The proposed new configuration uses a basic, actuated, nonlocking controller; 25-m (85-ft) long, delayed-call loop detector at the stopline; and two extended-call detectors upstream to give protection to the dilemma zone.