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Traffic Signal Systems Operations and Design: Isolated Intersections
Figure 48.
Traffic control
process model
When you have completed the reading, prepare answers to the following questions.
1.
What is the purpose of the ring barrier diagram?
2. How is timing represented in a ring barrier diagram?
3. Why use a ring barrier diagram instead of a conflict matrix to describe the sequencing of phases?
4. What is the difference between a
movement
and a
phase
?
Separating and Sequencing Movements
The primary function of a traffic signal is to safely separate and sequence the movement of vehicles traveling
through an intersection so as to minimize the probability of crashes and to maximize the flow of vehicles.
The “separation” of movements in time is accomplished by inserting the change and clearance timing intervals
(displayed to the vehicle user as yellow and red clearance indications) between conflicting movements. The
change and clearance intervals will be discussed later in this book, in Chapter
9. The “sequencing” of vehicle movements is the subject of this current chapter.
The sequencing of movements is accomplished through the sequencing of
displays or indications to which users respond. The four-component traffic
control process model, introduced in Chapter 1 and shown in Figure 48,
shows the interdependencies of the user, the detector, the controller, and the
display at a conceptual level. Here the dependence of the user on the display
is clear: the user responds in a safe and appropriate way to the information
conveyed in the display. But if we take a closer look at the actual hardware
used in the field, we can better see the detector-controller-display linkages
as well.
A
ctivity
13: P
hasing
, R
ings
,
and
B
arriers