lecture #6 chapter 16: principles of intersection signalization

Lecture #6Lecture #6

Chapter 16: Principles of Intersection Signalization

ObjectivesObjectives

Understand allocation of time and its effects at signalized intersections

Understand effect of design parameters on operations

Understand concept of delay and how it relates to the traffic stream

Modeling Intersection Modeling Intersection DeparturesDepartures

For an hour of green, how many departures can there be?

s = saturation flow rate, vphgpl

h = saturation headway, sec

3600 = seconds per hour

hs

3600


For an hour of green, how many departures can there be? (revisited)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

1 2 3 4 5 6 7 8

h e1

e2 e3

3211 eeel


So, how much time does it take to clear a queue?

T = Time to clear a queue, sec l1 = Start-up lost time, sec

h = Saturation headway, sec N = Number of vehicles in the

queue, veh

NhlT 1

Average Headway Per Vehicle

0

1

2

3

4

5

1 2 3 4 5 6 7 8 9

Queue Length (veh)

Hea

dw

ay (

sec)


How much time do we have to clear a queue?

gi = effective green time for movement i, sec

Yi = Sum of yellow plus all-red time for movement i, sec

t1 = start-up lost time, sec

tL = total lost time per phase, sec, tL=t1 + t2

t2 = clearance lost time, sec

Liii tYGg


For one hour of operation, how many vehicles can be served?

ci = capacity of lanes serving movement i, vph or vphpl

si = saturation flow rate for movement i, vphg or vphgpl

gi = effective green time for movement i, sec

C = signal cycle length, sec

C

gsc iii

An Example IntersectionAn Example Intersection

Task 1: Allocate the green time to the critical movements

Task 2: Find the optimum cycle length

1000 vph

600

vph

800 vph

400

vph


What do you need to know? – Demand volumes = {see figure}– Saturation flow rates = 3600/2 = 1800 vphgpl

– Lost time (tL) Start-up (t1)= 2 sec/phase

Clearance (t2)= 1.5 sec/phase

– Number of phases (N) = 2 phases/cycle– Lane configuration = number of lanes– Time available = 3600 sec/hr


How much time do we have for service?

TG= time available for effective green allocation within the hour

N = number of phases in a cycle

C = cycle length, sec

tL = total lost time per phase, sec, tL=t1 + t2

C

NtT LG 13600


How many vehicles can we serve?

TG= time available for effective green allocation within the

hour

h = Saturation headway, sec

Vc = maximum sum of critical lane volumes, vph

C

Nt

hh

TV LGc 1

3600


What is the shortest cycle that can serve the demand volumes?

– Solve for C:

– Substitute VEB+VNB = Vc

– Do you see any problems with this cycle length?

h

VNt

Cc

L

/36001

min


How can we adjust the cycle length in a way that would address these problems?

hcvPHF

VNt

Cc

L

/3600)/)((1

min

Left Turn VehiclesLeft Turn Vehicles

What different intersection geometric designs are used to accommodate left turns? – Shared lane– Exclusive left turn lane

Left Turn VehiclesLeft Turn Vehicles

How can traffic signals provide service to left turns? – Permitted – Protected – Protected-permitted combination

Adjusting for Left Turn Vehicles Adjusting for Left Turn Vehicles

Using Through Vehicle EquivalencyUsing Through Vehicle Equivalency What is through vehicle equivalency?

fLT = left turn adjustment factor

PLT = proportion of left-turning vehicles

ELT = left-turn equivalent

so = saturation flow rate for through vehicles

s = adjusted saturation flow rate

In the same amount of time {say 50 sec}, the left lane discharges 10 through vehicles and 5 left-turning vehicles, while the right lane discharges 25 through vehicles.

)1(1

1

LTLTLT EPf

ConclusionConclusion

New Homework Assignment: – Check web for HWK #3

Homework Assignment due: – Assignment #2

Lab Announcements– Data collection Monday, next week

lecture #6 chapter 16: principles of intersection signalization

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