INTRODUCTION (ECI 256)Traffic Flow Traffic ControlTraffic Flow, Traffic Control 

and a Case Studyy

Yi‐Ru ChenYi Ru ChenFall 2011

How many cars on earth?How many cars on earth?

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Where are bottlenecks?Where are bottlenecks?

• Google Map Traffic: up‐to‐date traffic conditions to help you plan your routes.p y p yhttp://maps.google.com

• PerformanceMeasurement System• Performance Measurement Systemhttp://pems.dot.ca.gov

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Why does congestion occur?Why does congestion occur?DEMAND > CAPACITY

D d

FLOW  RATE

Demand

C itCapacity

Observed flow

t8 am 5 pm t8 am 5 pm4

Flow(veh/hr), Density(veh/mile), and Speed(mile/hr)

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Flow(veh/hr), Density(veh/mile), and Speed(mile/hr)

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Flow(veh/hr), Density(veh/mile), and Speed(mile/hr)

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The Concept of Highway Capacity(Field Observations)

1800

2000

80

90

100

1200

1400

1600

our) 60

70

80

hour)

800

1000

Flow

 (veh

/ho

40

50

Speed (m

ile/h

200

400

600

10

20

30

0

0% 5% 10% 15% 20% 25% 30%

Occupancy (%, Fast lane)

0

0% 5% 10% 15% 20% 25% 30%

Occupancy (%)

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Approximate RelationsApproximate Relationsqmaxmax

Kc Kjam

uuf

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CapacityCapacity

The capacity of a transportation system:

The maximum number of vehicles/passengers “per p g punit time” that can be accommodated under given conditions w/ a reasonable expectation of poccurrence. – Capacity is independent of demandp y p

– Capacity depends on traffic composition

– Capacity is a probabilistic measure; an acceptable p y p ; pexpectation of occurrence. 

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Ideal capacityIdeal capacity

• Maximum hourly flow rate under ideal conditions– Lane width (>= 12FT)

– Lateral clearance (>=6FT)

– Number of lanes (>= 5/DIR)

– Interchange density(<=0.5/MILE)

– All passenger cars

– Familiar drivers

– Good weather conditions

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http://streetsforall.files.wordpress.com/2010/09/levelsservice.jpg

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CONTROL OF URBAN ARTERIALS

1. No control  (e.g., roundabouts)2 Stop/Yield control2. Stop/Yield control3. Signal control

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RoundaboutsRoundabouts

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Stop/Yield controlled intersectionsStop/Yield controlled intersectionsReturn

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Si l ll d i iSignal controlled intersections

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“Warrants”

Does the situation warrant a signal?gMUTCD(Manual on Uniform Traffic Control Devices)

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Traffic Signal Control: NEMA(National Electrical Manufacturers Association)

diagram phasesdiagram, phases

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Signal Control OperationsSignal Control Operations

• Pre‐timed or fixed‐time– Cycle length, phase sequences, green times, offsets are all pre‐

determined and fixed for a period of time (such as morning peak)Generally needs no sensors– Generally needs no sensors

– Mostly found on downtown streets, or streets with fixed traffic demand patterns.

• Semi‐actuatedll d d h l– Sensors are installed on minor street to detect vehicle presence. Green 

rest on main street until a vehicle call from minor street– Responsive to traffic demand changes– Usually found on major/minor street intersectionsy j /– Cycle  length and  phase sequences are variable

• Fully‐actuated– Sensors are installed on all approaches

R i t h i t ffi d d– Responsive to changes in traffic demand– Cycle  length and  phase sequences are variable

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The Italian JobThe Italian Job

http://www.youtube.com/watch?v=hvj9vhA8ixY 22

Controllers (solid‐state)Controllers (solid state)

Econolite 2070

ControllerControllercabinet

E l 2070Eagle 2070Inside a controller cabinet 23

Actuated signalsActuated signals

• A signal that is actuated by the arrival of individual vehicles on one or more approaches. The phases and green times vary from cycle to cycle Cycle length can alsofrom cycle to cycle. Cycle length can also change in response to traffic demand.

idside

main

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Signal coordinationSignal coordination FOR GOOD PROGRESSION AND LESS DELAY

t ff tNB

xtoffset

Ltoffset=block length / progression speed

S

progression speed=L/S

ttCoordination for NB Traffic

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Level of ServiceLevel of Service

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CASE STUDY: FIX I 5 ProjectCASE STUDY: FIX I‐5 Project

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CHANGES IN FREEWAY FLOW PATTERNS

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Volume ChangesVolume Changes

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Detour RoutesDetour Routes

H l T ffi Fl US50 EB C it l A (313780)Hourly Traffic Flow on US50 EB- Capitol Ave. (313780)

7,000

5,000

6,000

c F

low

Before

NB Closure

3,000

4,000

rly

Tra

ffic NB Closure

SB Closure

open

Aft

1,000

2,000

Ho

u After

-

0 1 2 3 4 5 6 7 8 9 10 1112 13 14 1516 17 18 1920 21 22 23Time of Day

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Unaffected RoutesUnaffected Routes

Hourly Traffic Flow on SR99 NB - 12th Ave (312562)

7,000

5,000

6,000

w Before

3,000

4,000

y T

raffic

Flo

w Before

NB Closure

SB Closure

open

1 000

2,000

,

Hourly

After

-

1,000

0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223

Time of Day

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