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Chapter 9: Right of Way Change: Change and Clearance Intervals
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In Chapter 9, you will learn about the vehicle change and clearance intervals, the timing intervals during
which yellow and red, respectively, are displayed. Signalized intersections clearly and unambiguously
assign right-of-way to specific movements in such a way that green is never displayed for conflicting
movements at the same time. Thus, the transition from the green for one movement to another is an
important process, one that must be done in way that maximizes safety for both the drivers that are
currently being served and those about to be served. This is accomplished through the clearance and
change intervals.
Like many parts of the signal timing process, technology and human factors must be considered together.
How fast do drivers respond to a newly displayed yellow indication? What is the variation of this response
among drivers? How does the variation in the approach speed of the drivers, and the distance that they are
upstream from the intersection, affect their response? How much of a safety factor should be built into
this change and clearance process? You will explore some of these questions in the activities that follow
in this chapter.
When you have completed the activities in this chapter, you will be able to
•
Describe the process for setting the yellow and red clearance times
•
Describe the purpose and method of calculation of the vehicle change and clearance intervals
•
Describe the different responses of drivers to the yellow indication based on their location upstream
of the intersection
•
Compare field data with the theoretical basis of stopping
•
Describe driver behavior at the onset of the yellow interval
•
Determine the vehicle change and clearance intervals
•
Describe the factors considered when the yellow and red clearance intervals are set by practicing
traffic engineers
This chapter begins with a
Reading
(Activity #52) on the change and clearance intervals. The chapter then
proceeds to three activities including an assessment of your understanding of the change and clearance
intervals (Activity #53) and activities in which you observe drivers responding to the yellow and red
displays using field data (Activities #54 and #55). A design activity (Activity #56) follows in which you
determine the change and clearance intervals for your design problem. The chapter concludes with an
In
Practice
activity (Activity #57) in which you compare the results of your design work with the
Traffic
Signal Timing Manual
.
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Right of Way Change: Change and Clearance Intervals