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Chapter 6: Timing Processes on One Approach
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The duration of the green interval for an actuated controlled intersection depends on the interaction of the
traffic demand and the actuated control settings. In Chapter 6, you will learn about two of these settings
that are so crucial to the efficient operation of the intersection: the minimum green time and the passage
time. You will consider these two timing parameters in the context of a related component: the placement
and length of the detection zone. You will learn that, in practice, you need to decide what conditions you
will tolerate. Do you want to risk that the green will terminate too soon and leave some vehicles unserved?
Or, do you want to risk that the green will not terminate soon enough, resulting in wasted green time?
Balancing these risks is one of the keys to efficient and effective signal timing.
When you have completed the activities in this chapter, you will be able to
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Describe the interaction of the minimum green time, the passage time, and the detection zone length
in producing efficient intersection operation
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Describe the timing processes for actuated traffic control
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Describe how the length of the detection zone affects the setting of the basic timing parameters
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Relate the length of the detection zone to the duration of the green indication
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Relate the length of the minimum green time to the efficient operation of a phase
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Describe the variation of vehicle headways in a departing queue
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Establish a desired maximum allowable headway
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Relate the maximum allowable headway to unoccupancy time
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Determine the vehicle extension time based on the length of the detection zone and the desired
maximum allowable headway
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Select a maximum allowable headway
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Compare headway distributions for one lane and two lane data
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Select passage time values for one lane and two lane approaches
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Contrast design values with those recommended in practice
This chapter begins with a
Reading
(Activity #30) on the relationship between the minimum green time,
the passage time (or vehicle extension time), and the detection zone length. The chapter then proceeds to
eight activities including an assessment of your understanding of the basic concepts of passage time and
detection zone length (Activity #31), four discovery activities in which you will learn about the timing
processes through observation of simulation, particularly the factors that should be considered when the
minimum green time and the vehicle extension time parameters are set, for a given length of the detection
6
Timing Processes on One Approach