Decision-Making Guide for Traffic Signal Phasing (2020) / Chapter Skim
Currently Skimming:
Pages 47-54
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 47... ...
39 6 Phase Sequence Like the selection of left- and right-turn phasing mode, the sequence of phases at an intersection can have impacts on safety and traffic operations. Phase sequence decisions are often closely related to the leftturn phasing mode.
|
From page 48... ...
40 Figure 11 - Typical Phasing Diagram for Leading Left-Turn Sequence (Adapted from NCHRP 2015) Figure 12 - Typical Phasing Diagram for Lagging Left-Turn Sequence (Adapted from NCHRP 2015)
|
From page 49... ...
41 Figure 13 - Typical Phasing Diagram for Lead-Lag Left-Turn Sequence (Adapted from NCHRP 2015) 6.2 Phase Sequence Considerations Some agencies use the same phasing sequence at all (or most)
|
From page 50... ...
42 Figure 14 - Representation of Yellow Trap (Adapted from NCHRP 2003) The Yellow Trap can occur when pairs of opposing approaches have any of the following characteristics.
|
From page 51... ...
43 • At intersections with a left-turn phase on both opposing approaches, the Yellow Trap can be prevented by ensuring that the through movement phases on opposing approaches end at the same time. This means that if a vehicle actuates one left-turn phase, but the opposing phase is not actuated, the signal must still serve both phases simultaneously.
|
From page 52... ...
44 This advantage only exists with protected-permissive left-turn phasing mode, not with protected-only mode. Furthermore, the advantage in efficiency should be weighed to account for operational inefficiencies due to countermeasures needed to prevent the Yellow Trap.
|
From page 53... ...
45 Figure 15 - Limited Left-Turn Bay Storage Lengths (Adapted from NCHRP 2015) Where the left-turn storage bay is relatively short and left-turn volume is high, a reserviced left-turn phase may be beneficial.
|
From page 54... ...
46 Lagging left turns are sometimes used at closely spaced intersections, such as those at a diamond interchange. Lagging left turns may be more efficient when used for downstream left turns, but the specific turning movements most appropriate to lag should also be identified using a time-space diagram.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.