Lecture #11Lecture #11

Signal Coordination: Chapter 22

Objectives

Factors affecting coordination Basic theory of signal coordinationApplication to arterial progression

Factors Affecting Coordination

BenefitsPurpose of signal systemFactors lessening benefitsExceptions to the coordinated scheme

Concept: Maximize Progression By Adjusting

Offsets

0 30 60 90 120 150 180 210

t1

Time (sec)

t2

1st Signal

2nd Signal

3rd Signalt3

Dis

tanc

e (f

t)

Note: Definitions of offset vary, but text convention is offset is t2 – t1 and t3 – t2

Benefits of Signal Coordination

Stops and DelayPerformance index: combining measuresCost =A X (total stops) + B X (total delay)What are some other benefits?

Engineering Options

What type of system is it?Which movements will be progressed?What is the objective?What happens if you can not achieve the

objective?

Factors Lessening Benefits

Inadequate roadway capacitySide frictionComplicated intersection timing plansWide variability in traffic speedsShort signal spacingHeavy turn volumes {see figure 22-3}

Time Space Diagrams and Ideal Offsets

What is an offset?What is an ideal offset?

0 30 60 90 120 150 180 210

t1

Time (sec)

t2

1st Signal

2nd Signal

3rd Signalt3

Dis

tanc

e (f

t)

One-Way Progression

For one-way progression, what do you need to know to estimate ideal offsets?

How do you construct a time-space diagram?

Can specify offsets relative to one (master) intersection

0 30 60 90 120 150 180 210

t1

Time (sec)

t2

1st Signal

2nd Signal

3rd Signalt3

Dis

tanc

e (f

t)

Effect of Queued Vehicles

Q number of vehicles queued per lane (veh/lane) H discharge headway of queued vehicle (sec/veh) Loss1 loss time associated with vehicles starting from rest at

the first downstream signal (sec)

)()( 1LossQhS

Lidealt

How do you determine the offset with queuing?

Different Types of Progression

What are the different types of progression?– Simple– Forward– Flexible– Reverse– Simultaneous

Two-Way ProgressionTwo-Way Progression

Progression in one direction suffersSegment offsets tSB+tNB = nC

Maximizing bandwidth– Popular– Limited

Two-Way Progression (Cont.)Two-Way Progression (Cont.)

Simultaneous progression– Closely spaced intersections– Queue management

Alternate progression– Uniform block length– 50:50 split

N the number of blocks with simultaneous green How do you determine N?

S

NLC

2

0 30 60 90 120 150 180 210Time (sec)

1st Signal

2nd Signal

3rd SignalD

ista

nce

(ft)

1000 ft intersection spacing2 lanes in each directionsC = 60 sec w/ 50:50 split

4th Signal

5th Signal

What is the progression speed?What is the nonstop volume?

Working Line

Two-Way Progression (cont.)Two-Way Progression (cont.)

What about arterials with non-uniform intersection spacing?

0 ½ C C 1½ C 2C 2½ C 3C 3½ CTime (sec)

Dis

tanc

e (f

t)

Working Line

0 ½ C C 1½ C 2C 2½ C 3C 3½ CTime (sec)

Dis

tanc

e (f

t)

Working Line

A Signal Coordination StudyA Signal Coordination Study

Go to the field and ride through the system– Do you see unused green time at down stream

signals?– Do you arrive at signals with standing queues?– Do you arrive on red?– Is the flow in the other direction significant?

Sketch out network with flow patterns Which cycle length is most appropriate?

Oversaturated ConditionsOversaturated Conditions

Removal of intersection blockage– Address root causes– Update signalization– Use novel signalization to reduce extent of congestion– Provide more space– Prohibitions vs enforcement vs resulting problems– Consider other options

Oversaturated ConditionsOversaturated Conditions

Signal based remedies– Metering plans– Shorter cycle lengths – Equity offsets – Imbalanced split