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Abstract
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[SafetyLit note: The name, Mats Järlström, has become widely known among traffic engineering experts because he was fined US$500 by the state of Oregon for criticizing the state's traffic signal timing without first obtaining a professional engineering license. Järlström forwarded to the Institution of Transportation Engineers his detailed criticism of existing signal timing with a recommendation for a new formula and guidelines. The ITE has formally accepted Järlström's recommendations. This article is a discussion of the formulas and how they improve intersection safety.]
Since the yellow indication was first added to traffic signals in 1920, the proper interval duration has been robustly debated. Seemikngly, the timing of the yellow indication appears straightforward. However, determining the illumination interval is quite intricate since it is part of a complex system of physical and human-made laws, technology, and behavior that all must operate compatibly.
In 1960, Denos Gazis, Robert Herman, and Alexei A. Maradudin (GHM) provided a scientific solution to the yellow change interval question in their paper, "The Problem of the Amber Signal Light in Traffic Flow."2 GHM presented a kinematic solution to a binary STOP or GO dilemma when a driver is faced with the onset of a yellow signal indication. The problem GHM solved and eliminated was an area in the roadway known as the "dilemma zone", where a driver-vehicle complex could neither STOP safely and comfortably nor GO without the need to violate the red or accelerate unsafely into the intersection.
GHM's solution to regulate a yellow change interval first appeared in the 1965 ITE Traffic Engineering Handbook, and it has become known as the kinematic equation. However, GHM's solution is limited to vehicles traveling through level intersections at constant velocity, which does not include vehicle deceleration to execute safe turning maneuvers. This article presents a brief review covering GHM's original solution and Mats Järlström's extended kinematic equation which allows for vehicle deceleration and turning maneuvers.
Language: en |