Basic Signal Timing and Coordination Principles

1

• Topic 3
• Basic Signal Timing and Coordination Principles

2
Signal System Classification

• Traditional Systems
• Closed-Loop (Field Master)
• Centralized Computer Control
• Adaptive

3
Signal Timing Process
Data Collection
Field Implementation
Signal Timing Development
4
Basic Terminology

• Cycle
• Phase Split
• Phasing Sequence
• Offset
• Force-off

5
Cycle Length and Split

• Cycle Length

All signals must have a common cycle length to
achieve coordination

• Split

Split Green Yellow All-red
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Signal Coordination
Intersection 1
Intersection 2
East Bound
7
Offset

• Offset is the time difference between two
  reference points
• Offset must be specified by
• Phase
• Begin/end phase
• Offset 0 cycle length

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Offset
Local zero
Local zero
? 2,5
? 1,5
? 1,5
? 2,6
? 4,8
? 2,6
? 4,8
? 3,7
When the local zero occurs at 40 sec of the
master clock We say the Offset 40 sec
9
Time-Space Diagram One-way Street
G25
Y5
R30
1
?2
?2
?8
?8
?4
?4
?6
?6
EB Band
G35
Y5
R20
2
?2
?2
?8
?4
?8
?4
?6
?6
Time
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Time-Space DiagramTwo-way Street
1
G25
Y5
R30
?2
?2
?8
?8
?4
?4
?6
?6
EB Band
WB Band
G35
Y5
R20
?2
?2
2
?8
?4
?8
?4
?6
?6
Time
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Questions
Question 1 ?2 and ?6 at intersection 1 turn
to green at 60 sec, ?2 and ?6 at intersection 2
turn to green at 20 sec, what are the offset s at
the two intersections, assuming the offset is
referenced to the start of green of ?2 and ?6?
Question 2 Given the offsets number in
Q1, what will the offsets be if the offsets are
referenced to the end of green of ?2 and ?6?
Question 3 If the travel speeds are
different for the two directions, will it affect
the above offset results?
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Offset and Transition

• Synch point/clock the time all offsets are
  referenced to. It is also called Master Clock
  Zero. It is usually set at 1200 300 a.m. when
  traffic is light.

1200 a.m. (Master Zero)
Master Zero
Master Zero
Master Zero
Local Zero
Local Zero
Local Zero
Offset
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Example

• If the Synch point is set at 300 a.m., for a
  signal operating at an 90-sec cycle and an offset
  of 40, what would be the master clock timer and
  the local clock timer at 1120 a.m.?

14
Transition Methods

• Transition occurrences
• Plan change
• Preemption
• Pedestrian
• Transition methods/algorithms
• Dwell
• Max Dwell
• Add
• Subtract
• Shortway

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Example
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Offset and Transition
?1
?1
?2
?2
1
?8
?4
?6
?6
?5
?5
WB 8 sec
EB 20 sec
2
?2
?8
?4
?8
?4
?6
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Bandwidth(Dual LT Leading)
?1
?1
?2
?2
1
?8
?4
?6
?6
?5
?5
WB 8 sec
EB 20 sec
2
?2
?8
?4
?8
?4
?6
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Bandwidth - Adjusted(Dual LT Leading)
?1
?1
?2
?2
1
?8
?4
?6
?6
?5
?5
WB 12 sec
EB 20 sec
2
?2
?8
?4
?8
?4
?6
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Bandwidth - Initial(Lead/Lag)
?1
?1
?2
?2
1
?8
?4
?6
?6
?5
?5
WB 12 sec
EB 20 sec
2
?2
?8
?4
?8
?4
?6
20
Bandwidth - Adjusted(Lead/Lag)
?1
?1
?2
?2
1
?8
?4
?6
?6
?5
?5
WB 20 sec
EB 20 sec
2
?2
?8
?4
?8
?4
?6
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MOEs

• Bandwidth Concept (PASSER II)
• Bandwidth, seconds
• Bandwidth Efficiency Bandwidth/Cycle
• Attainability Bandwidth/gmin
• System-Wide Delay (Synchro)
• System-wide Stops and Delay (TRANSYT-7F)

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Yellow Trap
Yellow trap is a situation faced by a left-turn
movement when the display of yellow occurs to
both the left-turn phase and the adjacent through
phase, but the opposing through is not
terminating.
(1)
(3)
(2)
(5)
(4)
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Dallas phasing has louver that through vehicles
cannot see
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Left-turn phase about to end
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Through movements move both directions. Left-turn
yield to opposing through.
26
Yellow trap occurs when the leading left-turn
sees yellow and thinks the opposing through phase
will also end
27
Dallas phasing does not display yellow, and
left-turn sees green ball and is supposed to
still yield.
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When left-turn sees yellow, the opposing phase
also about to end
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Main street phases end, side street phases begin
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Yellow Trap

• Only the leading left-turn has the yellow trap
  with protected/permitted phasing
• Dallas Phasing solves the "yellow-trap" problem
  by holding a solid green indication.
• Louvers are used to shield the left-turn display
  so that the green display in the left-turn signal
  cannot be easily seen by thru drivers.
• When can a yellow trap occur with standard PPLT
  with left-turns leading or lagging?

http//projects.kittelson.com/pplt/LearnAbout/Lear
n3.htm
http//projects.kittelson.com/pplt/displays/dallas
_doghouse_lag.htm
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Summary

• Offset
• Bandwidth
• Time-Space Diagram

• What is Yellow Trap and when it occurs?
• What is the main purpose of using Lead-Lag
  phasing? Can Lead-Lag phasing increase an
  intersection capacity?
• What is the exception that a different cycle
  length can be used at an intersection while still
  maintaining coordination?

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Lab Exercise

• Use the Kietzke system (3 signals) to perform the
  following exercise.

• Use the Synchro offset optimization (keep cycle
  length and splits unchanged) and answer the
  following questions
• What are the phasing sequences at each
  intersection?
• How are the offsets referenced and what are the
  offsets?
• Examine the timing solution and indicate where
  stops may occur if driving on the main street
  both directions.
• Can you further improve the bandwidth by changing
  the phasing sequences from Synchro? Answer the
  same questions above.
• Which intersection is controlling the bandwidth?

33
Lab Exercise

• Use the Boulder Highway system (3 signals) to
  perform the following exercise.

1. Understand the existing timing sheets and compare
   with Synchro coding.
2. Use the Synchro offset optimization (keep cycle
   length and splits unchanged) and compare Synchro
   timing solution with the existing (bandwidth)
3. How was the phasing sequence changed at each
   signal? Can you further improve the bandwidth by
   changing the phasing sequences from Synchro?
4. Which intersection is controlling the bandwidth?
5. Try only with two intersections (Harmon and
   Tropicana) and see how the solution changes.

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Signal Timing Sheets (NextPhase)

• Boulder Hwy/Tropicana Intersection
• 1.1 Schedule of timing plans
• 2.3.x Information of a timing plan cycle,
  split, offset, sequence
• 2.4.x Phasing sequence
• 2.5.x Phase data (min green, yellow, all-red
  etc.)
• 4.2.1- Phase designation (direction/movement) and
  ring structure

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Lead/Lag Phasing
WB 36 sec
EB 16 sec
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