Macroscopic Fundamental Diagram for Urban Freeways Victor L Knoop Serge P Hoogendoorn Goal Describe traffic states and future traffic states An easy description of traffic ID: 780578
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Slide1
Empirics of a Generalized Macroscopic Fundamental Diagram for Urban Freeways
Victor
L. Knoop, Serge P. Hoogendoorn
Slide2GoalDescribe traffic states
and
future traffic statesAn easy description of traffic allows for large scale controlMFD: describe the flow (speed) as function of nr of vehiclesUse for control: routing, perimeter control
Slide3Macroscopic Fundamental Diagram
Apparently
quite
good
, but
only with homogeneous networks
Main questions1) Can
produciton for inhomogeneous traffic conditions be
described by an MFD?2) How to quantify
the effect of
inhomogeneity
=>
Emperical
observations
Slide4Empirical study – siteA10 freeway
21 km
10
months, daytimeMostly 3 lanes80-100 km/h speed limitDual loop detectors<500 meter sectionsSpeed, density=> accumulation & production
Slide5Road impression
Slide6Predicting production: methodology
Split data set
(
calibration/validation)Create MFDFor validation set:predict production based on accumulationusing
MFD
Slide7Fit and predictive power
Moving
averageSevere errors in estimationof production near capacity
Slide8Generalized MFDAccumulation =>
Inhomogeneity
=>
Production as function of accumulation and inhomogeneityInhomogeneity expressed as stdev of density
Production =>
Slide9Generalized MFD
Accumulation
=>
Inhomogeneity =>Color = productionInterpolation as predictorMeasure accumulation &
inhomogeneity => predict production
Slide10Quality of predictionPredicted by
interpolation
Slide11Fitting a functional formP(A)=A*(c
1
+c
2A+c3A2)-c4sHomogeneous traffic situationInhomogeneous traffic situation
Slide12Fitting a functional formP(A)=A*(c
1
+c
2A+c3A2)-c4s
Slide13Empirical evidence
Accumulation
=>
Inhomogeneity =>
Slide14Fit and predictive power (2)
Similar
to interpolationEasier to quantifyInterpretation of variables
Slide15Quality of fit
R
2
MFDGMFDQuality of fit0.850.86A>18 veh/km0.00160.39
Slide16Use in practiseBuffer traffic to
ensure
maximum
outflow to motorwayHold traffic further upstream, e.g.
Accumulation
A
c
.5 A
cAmax
LOS ALOS B
(Ac+Amax)/2LOS C
LOS D
Accumulation
Production
A
c
.5 A
c
(
Ac+A
max
)/2
A
max
Production
LOS A
LOS B
LOS C
LOS D
Slide17ConclusionsTraffic flow can be
descibed
at a high (area-
wide) levelTwo explanatory variables: accumulation & inhomogeneityPredictive power much increased by adding inhomogeneity