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Engenharia de Tráfego Rodoviário / Road Traffic Engineering MEC (Urbanismo, Transportes e Sistemas), MET, MPOT, MUOT 1
Mestrado Integrado em Engenharia Civil
Mestrado em Engenharia do Território
Disciplina: Engenharia de Tráfego Rodoviário
Prof. Responsável: Filipe Moura
Session 11: Capacity and LOS in Roundabouts
Methods
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Estimation Models
Statistical – Empirical
Probabilistic - Gap acceptance
Geometry and traffic inputs
Capacity Empirical methods
Gap acceptance
Analytical methods
Simulation Engenharia de Tráfego Rodoviário / Road Traffic Engineering MEC (Urbanismo, Transportes e Sistemas), MET, MPOT, MUOT 2
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Methods
EMPIRICAL
English (TRL)
Portuguese
French
Swiss
German
PROBABILISTIC
NAASRA (National Association of Australian State Road Authorities)
German
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Determining the circulation flow
NN
EW
S
Circulation flow Or
Conflicting flow Entry Circulation flows
N S-W E-W E-S
W N-S E-S N-E
S N-E W-E W-N
E W-N S-N S-W
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English and Portuguese Methods
Entry radius, r
Approach width, v
Entry width, e
Inscribed circle diameter, ICD
Entry angle, θ Effective length of flare, l’
Capacity is a function of six geometric parameters.
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Computation of flare length
• Entry flaring is localized widening at the point of entry. • Normal Roundabouts usually have flared entries with the
addition of one or two lanes at the give way line to increase capacity. Single lane entries e.g. those at Compact Roundabouts, should be slightly flared to accommodate large goods vehicles. Even a small increase in entry width may increase capacity.
• The average effective flare length, l', is the average length over which the entry widens. It is the length of the curve CF‘: • AB = e (entry width). • GH = v (approach half width at point G which is the best
estimate of the start of the flare). • GD is parallel to AH and distance v from AH (v is measured
along a line perpendicular to both AH and GD and, therefore, the length of AD is only equal to v if AB is perpendicular to the median at A).
• CF' is parallel to BG and distance ½ BD from the curve line BG
l’
A
B
H G
DC
F’
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English method
)( cce QfFkQ ×−×=
!
k =1" 0,00347 # " 30( ) " 0,9781
r
$
% & '
( ) " 0,05
*
+ ,
-
. /
2303XF =
)2,01(210,0 2Xtf Dc +=
MtD +
+=15,01
−
=1060ICDexpM
SvevX212 +
−+= '
)(6,1
l
veS −=
EFFICIENCY FACTOR
MAX STOCKAGE Cap.
CORRECTION Factor
ACCUM. Potencial
WITH
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Portuguese Method
)( cce QfFkQ ×−×=
−−−−= 05,0)1(431,3)30(00163,01r
k θ
247,335 XF =
)2,0457,0(611,0 2Xtf Dc +−=
MtD +
+=1983,01
EFFICIENCY FACTOR
MAX STOCKAGE Cap.
CORRECTION Factor
ACCUM. Potencial
−
=1060ICDexpM
SvevX212 +
−+= '
)(6,1
l
veS −=WITH
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French Method
Entry width
Inscribed circle diameter
Exit width
Triangular island width
Circulatory roadway width
Capacity is function of 5 geometric parameters
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French method
))5.3(1.01)(7.01330( −+×−= ENTQQ ce
Where
))8(085.01))(15/1(3/2( −−−+= ANNSEPQQQ stc
Qc – Conflicting flow;
Qs – exit flow (in the analysed approach);
Qt – circulating flow (passes in front of the analysed approach);
ENT – Entry width ;
ANN – Circulatory roadway width;
SEP – Triangular island width.
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Swiss method
Capacity – function of 3 geometric parameters
Number of entry lanes
Number of lanes in the roundabout
Distance among conflicting points, b
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Swiss method Ce =
1
!! (1500"
8
9Qg )
QD= !Qc +"Qs
Ce – Entry capacity QD – Disturbing flow TCUe – Saturation flow at the entry Qs – Exit flow; Qc – Circulation flow (in the circulatory roadway);
Coefficients α – influence of exit flow (depends on the distance between conflicting points)
β – reduction factor γ – flow distribution
Values of β (nº of lanes in the ring)
1 lane 2 lanes 3 lanes 0,9 – 1,0 0,6 - 0,8 0,5 – 0,6
%100..e
ee C
QTCU γ=
Values of γ (nº of entry lanes)
1 lane 2 lanes 3 lanes 1,0 0,6 - 0,7 0,5
Engenharia de Tráfego Rodoviário / Road Traffic Engineering MEC (Urbanismo, Transportes e Sistemas), MET, MPOT, MUOT 12
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German method
Number of entry lanes
Number of lanes
Capacity – function of two geometric parameters
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German method
ce QQ ×−= 740,01218
ce QQ ×−= 532,01250
ce QQ ×−= 500,01380
ce QQ ×−= 420,01409
Number of lanes
Entry circulatory Capacity of entry
1 1
2 or 3
2 2
3
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NAASRA method (Australian)
fhve – Heavy vehicles adjustment factor;
qc – conflicting flow (pcu/s);
α – Critical Gap;
β – Follow-up headway;
Δc – intra-bunch headway (headway between vehicle circulating within the roundabout)
( ) ( )
β
α
c
cc
q
qccc
Hvec eeqqfQ
−
Δ−−
−
Δ−×=
113600
=
β3600
Hvef
0>cq
0=cq
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German method of gap acceptance
( )cc
c
qn
c
ccHvec e
nqfQ Δ−−−×
×
Δ−×= βα
β5.036001
c
ccnqΔ
≤
c
cc
nqΔ
>
fhve – Heavy vehicles adjustment factor;
qc – conflicting flow - traffic volume on the circulatory roadway (pcu/s)
Nc – Number of circulatory lanes (in roundabout)
α – Critical Gap (=4.1sec.)
β – Follow-up headway (=2.9sec.)
Δc – intra-bunch headway - minimal time gap on the circulatory roadway
(=2.1sec.).
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Case study - data
ICD = 70 m
Entry width = 7,0 m
Lane width = 7,0 m
Effective lenght of flare = ∞
Island width = 3,5 m
Diameter of the inner circle = 9,0 m
Entry radius = 40 m
Entru angle = 40º
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Case study – results
0
500
1000
1500
2000
2500
3000
0 150 300 450 600 750 900 1050 1200 1350 1500 1650
Fluxos de Conflito (uvle/h)
Capa
cida
de d
a En
trada
(uvl
e/h)
Inglês Português Francês SuiçoAlemão AlemãoGap NAASRA
Lane
capa
city (
pc/hr
)
Conflict volume (pc/hr)
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Other methods
Ex-JAE
HCM 2000
Sidra (evolution of the australian method)
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Comercial Software
ANALÍTICAL & EMPÍRICAL
ARCADY
RODEL
aaSIDRA
KREISEL
GIRABASE
HCS2000
SIMULATION
CORSIM
INTEGRATION
SIMTRAFIC
VISSIM
PARAMICS
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