Download - Capacity and Level of Service at Signalized
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capacity and level of service
at signalized intersection• The level of service at any intersection on highway has a significant effect on theoverall operating performance of that highway. Thus improvement of the level ofservice oat each intersection usually results in an improvement of the overall
Operating performance of the highway.
Analysis procedure that provides for the determination of capacity or
lever are:
a. Flow b. Distribution of traffic
c. Geometric characteristics
d. And ignalization system
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!".! D#F$%$T$O% OF O 'O&&O% T#(&
• Permitted turning movements is made within gaps of opposing traffic stream
or through a conflicting pedestrian flow.
• Protected turns are those protected from any conflicts with vehicles in an
opposing stream or pedestrians on a conflicting crosswal).
• Yellow change and red clearance interval is the sum of the intervals *given
in seconds+ that are provided between phases to allow vehicular and pedestrian
traffic to clear the intersection before conflicting movement are released.
• Geometric conditions is a term used to describe the roadway characteristic of
the approach.
• Signalization conditions is the term used to describe the signal operation.
• Flow rate v/s pro,ected demand *v+ on a approach or lane group to the
saturation flow rate *s+
• Lane group consists of one or more lanes that have a common stop line- carry
a set of traffic streams- and whose capacity is shared by all vehicles in the
group.
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• An analysis period (T is the time intervals selected
to evaluate am intersection by applying the procedure
once.
• The study period is the time period for which the
results of the analysis are applicable and may consist
of one or more consecutive analysis periods.• !est in "al# mode enable for a phase- this mode will
dwell in wal) ecept when there are conflicting calls
• Pedestrian clear interval (P$% sometime )nown as
the pedestrian change interval allow pedestrian who
leaves the curb during the wal) interval to arrive at the
opposite curb or median.
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• &aimum rate of flow to sub,ect lane group that can
go through the intersection under prevailing traffic-
roadway- signalized conditions
• Overall capacity of the intersection is not considered.• #mphasised on suitable facilities movement of the
intersection.
•
/evel of service and capacity should be analysedseparately
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SAT,!AT&+' FL+" +! SAT,!AT&+' FL+"
!AT)
• The concept of saturation flow or saturation flow
rate*s+ is used to determine capacity of a lane group.
• &aimum flow rate on the approach or lane groupthat can go through the intersection under prevailing
traffic and roadway conditions when !""0 effective
green time is available.
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The critical v/c ratio -or the whole intersection
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A'ALYS&S L).)LS A'* P)!F+!A'$) )AS,!)S F+! L).)L +F
S)!.&$) AT S&G'AL&)* &'T)!S)$T&+'S
There are three *1+ analysis levels for determining the level of
services */O+
• Operational
• Design and
• 2lanning and preliminary engineering
!. Operational level uses detailed information on:
•.
Traffic•.Geometric
•.ignalization characteristics for a comprehensive analysis of the
intersections.
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3. Design analysis level is used when an intersection is being designed for a given
/O.
(e4uires:
5 Traffic 5Geometric
5ignalization characteristics
5Desired /O.
1. 2lanning and preliminary engineering analysis level uses
. basic and default values to evaluate a given intersection
. or planned overall eisting performance of a signalized intersection
. (e4uires least amount of site5 specific data.
&odes used for evaluating performance measures for 4uality operation at the
intersection:
. Automobiles
. 2edestrian
. 6icycle
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The per-ormance measures include0
• Demand volume-to- capacity ratio v/c
• Queue storage ratio
• Automobile delay
• Pedestrian circulation area
• Pedestrian perception score• Pedestrian delay for walking
• Bicycle delay
• Bicycle perception score for bicycles
The !" is considered as a performance measure and it iscomputed separately for each of the modes considered#
The in$uence area in analysis should be at least %&'ftbackward from the stop line of each leg of the intersection#
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1234 L).)L +F S)!.&$) $!&T)!&A AT S&G'AL&)*
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/O 'riteria for the Automobile &ode
These procedures deal with the computation of the level of
service at each lane group- intersection approach- and at the
intersection as whole.
TA6/# !".!
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L+S $riteria -or 'onautomotive (Pedestrian and
5icycle ode
The criteria for the nonautomotive modes are based on:
• cores computed from factors described as either performance
measures sure as:
•
2edestrian delay• $ndicators of the intersection characteristics
• 2edestrian corner circulation area
Table !".3 gives the relationship between the scores and the /O
for the nonautomotive mode.
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automo7ile can 7e categorized into -our (8 group
• Traffic characteristics
• Geometric design• ignal control
• Other
Traffic characteristics
The demand flow rate5vehicles that arrive at the intersection divided bythe analysis period.
The right5turn5on5red *(TO(+ flow rate is the 4uotient of the number of
vehicles that turn right during analysis period and is epressed in terms of
an hourly flow.
2latoon ratio5how well a movement group progresses through theintersection and depends on the percentage of vehicles that arrive during
the green indication
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• TAB( )'#* A+D TAB( )'#&
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The upstream -iltering ad9ustment -actor (&
,)#'-'#.)0%#123'#'.
• &nitial 6ueue is the number of vehicles that are at the intersection at
the start of the analysis period of the movement group under
consideration.• 6ase saturation flow rate*+ is the maimum rate of flow across the
stop line. $t is associated with the following conditions:o Traffice lanes at least !3 ft wide
o %o heavy vehicles in the traffic stream
o A flat gradeo %o par)ing
o %o buses that stop at the intersection
o #ven lane utilization
o %o turning vehicles
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The lane utilization ad,ustment factor *Flu+ is used
to ad,ust the ideal saturation flow rate The pedestrian flow rate 5
number of pedestrians in cross wal) that interrupt the flow of
right5turning vehicles during analysis period.
• The bicycle flow rate 7number of bicycles with a travel path
that results in an interruption of the flow of right 7 turning
vehicles from the approach under consideration during the
analysis period.
• The on5street par)ing maneuver rate 7 number of par)ing
maneuvers per during the analysis period that have an impact
on the intersection leg.
• The local bus stopping rate5the number of buses per hourduring analysis period that bloc) traffic by stopping
embar)ing or disembar)ing passengers within 38"ft.
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Geometric *esign
Geometric elements of the intersection that have some
impact or the flow of traffic.
%umber of lanes
Average lane width %umber of receiving lanes
Turn bay length
2resent of on5street par)ingApproach grade
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Signal control
elements provide input data for the signal control data are:
a. 2re5timed
b. semi5actuated
c. Fully actuated
d. And coordinated5actuated mode.
+ther
• The area type describe the activities in the are at which the
intersection is located.
• 9ave significant effect on:
peed
aturated volume at an approach.
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COMPUTATION OF
PEDESTRIANS ANDBICYCLES FACTOR
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