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Chapter 3: Whose Turn is it? Phasing, Rings, and Barriers
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The purpose of this activity is to test your understanding of the material covered in the Reading on ring
barrier diagrams. This includes gaining a basic level of understanding of the concept of rings and barriers,
and how they are used to safely separate the operation of conflicting movements at a signaled intersection.
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Describe NEMA phasing and the concept of rings and barriers
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List the phase numbers at a standard intersection with eight movements
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Draw and describe a ring barrier diagram in which there are two rings and eight phases
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Activity #13: “Phasing, Rings, and Barriers”
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Prepare a one page document that includes your results from Tasks 1 through 5
Sketch a four leg intersection, showing an exclusive left turn lane and one through lane on each approach.
Number each movement and list the phase number corresponding to the standard NEMA numbering
scheme that would control each movement.
Prepare a sketch of a ring barrier diagram that represents the condition described in Task 1.
Prepare a brief description of the timing process for this eight phase operation by describing the order and
manner in which each phase is served. Consider the various sequences that may occur depending on traffic
flow volumes.
Suppose the traffic demand for the east-west movements at a signalized intersection requires the following
times for each movement to be served. Draw a partial ring barrier diagram showing the sequence and the
timing of the phases controlling these movements. (See Table 7, following page.)
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What Do You Know About Phasing and Ring
Barrier Diagrams?