Topic 3
Basic Signal Timing and
Coordination Principles
CEE 764 – Fall 2010
Signal System Classification
 Traditional


Systems
Closed-Loop (Field Master)
Centralized Computer Control
 Adaptive
CEE 764 – Fall 2010
Signal Timing Process
Data
Collection
CEE 764 – Fall 2010
Signal Timing
Development
Field
Implementation
Basic Terminology





Cycle
Phase Split
Phasing Sequence
Offset
Force-off
CEE 764 – Fall 2010
Cycle Length and Split

Cycle Length
All signals must have a common cycle length
to achieve coordination

Split
Split = Green + Yellow + All-red
CEE 764 – Fall 2010
Signal Coordination
Intersection #1
Intersection #2
East Bound
CEE 764 – Fall 2010
Offset

Offset is the time difference between two
reference points

Offset must be specified by



Phase
Begin/end phase
Offset = 0 ~ cycle length
CEE 764 – Fall 2010
Offset
Local zero
ф 2,5
ф 1,5
ф 4,8
Local zero
ф 1,5
ф 2,6
ф 4,8
ф 2,6
ф 3,7
When the local zero occurs at 40 sec of the master clock
We say the Offset = 40 sec
CEE 764 – Fall 2010
Time-Space Diagram
One-way Street
#1
Y=5
G=25
2
6
R=30
8
2
6
4
8
4
EB Band
G=35
#2
8
4
2
6
Y=5
R=20
8
4
Time
CEE 764 – Fall 2010
2
6
Time-Space Diagram
Two-way Street
#1
Y=5
G=25
2
6
R=30
8
2
6
4
EB Band
8
4
2
6
Y=5
R=20
8
4
Time
CEE 764 – Fall 2010
4
WB Band
G=35
#2
8
2
6
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?
CEE 764 – Fall 2010
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 12:00 – 3:00 a.m. when traffic is
light.
12:00 a.m.
(Master Zero)
Local Zero
Offset
CEE 764 – Fall 2010
Master Zero
Local Zero
Master Zero
Local Zero
Master Zero
Example

If the Synch point is set at 3:00 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 11:20 a.m.?
CEE 764 – Fall 2010
Transition Methods

Transition occurrences




Plan change
Preemption
Pedestrian
Transition methods/algorithms





Dwell
Max Dwell
Add
Subtract
Shortway
CEE 764 – Fall 2010
Example
CEE 764 – Fall 2010
Offset and Transition
1
2
5
6
1
2
#1
8
8
4
CEE 764 – Fall 2010
5
6
WB:
8 sec
EB:
20 sec
#2
4
2
6
8
4
Bandwidth
(Dual LT Leading)
1
2
5
6
1
2
#1
8
8
4
CEE 764 – Fall 2010
5
6
WB:
8 sec
EB:
20 sec
#2
4
2
6
8
4
Bandwidth - Adjusted
(Dual LT Leading)
1
2
5
6
1
2
#1
8
4
8
4
CEE 764 – Fall 2010
6
WB:
12 sec
EB:
20 sec
#2
5
2
6
8
4
Bandwidth - Initial
(Lead/Lag)
1
2
2
1
#1
8
6
5
4
8
4
CEE 764 – Fall 2010
6
WB:
12 sec
EB:
20 sec
#2
5
2
6
8
4
Bandwidth - Adjusted
(Lead/Lag)
1
2
2
1
#1
8
6
5
4
8
4
CEE 764 – Fall 2010
6
WB:
20 sec
EB:
20 sec
#2
5
2
6
8
4
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)
CEE 764 – Fall 2010
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.
CEE 764 – Fall 2010
(1)
(2)
(3)
(4)
(5)
Dallas phasing has louver that through vehicles cannot see
CEE 764 – Fall 2010
Left-turn phase about to end
CEE 764 – Fall 2010
Through movements move both directions. Left-turn yield
to opposing through.
CEE 764 – Fall 2010
Yellow trap occurs when the leading left-turn sees yellow
and thinks the opposing through phase will also end
CEE 764 – Fall 2010
Dallas phasing does not display yellow, and left-turn sees
green ball and is supposed to still yield.
CEE 764 – Fall 2010
When left-turn sees yellow, the opposing phase also about
to end
CEE 764 – Fall 2010
Main street phases end, side street phases begin
CEE 764 – Fall 2010
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 leftturns leading or lagging?
http://projects.kittelson.com/pplt/LearnAbout/Learn3.htm
http://projects.kittelson.com/pplt/displays/dallas_doghouse_lag.htm
CEE 764 – Fall 2010
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?
CEE 764 – Fall 2010
Lab Exercise

1.
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:
•
•
•
2.
3.
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?
CEE 764 – Fall 2010
Lab Exercise

1.
2.
3.
4.
5.
Use the Boulder Highway system (3 signals) to
perform the following exercise.
Understand the existing timing sheets and compare with Synchro
coding.
Use the Synchro offset optimization (keep cycle length and splits
unchanged) and compare Synchro timing solution with the
existing (bandwidth)
How was the phasing sequence changed at each signal? Can you
further improve the bandwidth by changing the phasing
sequences from Synchro?
Which intersection is controlling the bandwidth?
Try only with two intersections (Harmon and Tropicana) and see
how the solution changes.
CEE 764 – Fall 2010
Signal Timing Sheets (NextPhase)
Boulder Hwy/Tropicana Intersection
1.
2.
3.
4.
5.
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
CEE 764 – Fall 2010
Lead/Lag Phasing
CEE 764 – Fall 2010
CEE 764 – Fall 2010